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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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package java.net;

import java.io.IOException;
import java.io.InvalidObjectException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CoderResult;
import java.nio.charset.CodingErrorAction;
import java.nio.charset.CharacterCodingException;
import java.text.Normalizer;
import jdk.internal.misc.JavaNetUriAccess;
import jdk.internal.misc.SharedSecrets;
import sun.nio.cs.ThreadLocalCoders;

import java.lang.Character;             // for javadoc
import java.lang.NullPointerException;  // for javadoc


Represents a Uniform Resource Identifier (URI) reference.
 Aside from some minor deviations noted below, an instance of this
class represents a URI reference as defined by
RFC 2396: Uniform
Resource Identifiers (URI): Generic Syntax, amended by RFC 2732: Format for
Literal IPv6 Addresses in URLs. The Literal IPv6 address format
also supports scope_ids. The syntax and usage of scope_ids is described
here.
This class provides constructors for creating URI instances from
their components or by parsing their string forms, methods for accessing the
various components of an instance, and methods for normalizing, resolving,
and relativizing URI instances.  Instances of this class are immutable.
 URI syntax and components 
At the highest level a URI reference (hereinafter simply "URI") in string
form has the syntax

[scheme:]scheme-specific-part[#fragment]

where square brackets [...] delineate optional components and the characters
: and # stand for themselves.
 An absolute URI specifies a scheme; a URI that is not absolute is
said to be relative.  URIs are also classified according to whether
they are opaque or hierarchical.
 An opaque URI is an absolute URI whose scheme-specific part does not begin with a slash character ('/'). Opaque URIs are not subject to further parsing. Some examples of opaque URIs are: 

mailto:java-net@java.sun.com
news:comp.lang.java
urn:isbn:096139210x

 A hierarchical URI is either an absolute URI whose
scheme-specific part begins with a slash character, or a relative URI, that
is, a URI that does not specify a scheme.  Some examples of hierarchical
URIs are:
 http://example.com/languages/java/
 sample/a/index.html#28
 ../../demo/b/index.html
 file:///~/calendar 
 A hierarchical URI is subject to further parsing according to the syntax

[scheme:][//authority][path][?query][#fragment]

where the characters :, /,
?, and # stand for themselves.  The
scheme-specific part of a hierarchical URI consists of the characters
between the scheme and fragment components.
 The authority component of a hierarchical URI is, if specified, either
server-based or registry-based.  A server-based authority
parses according to the familiar syntax

[user-info@]host[:port]

where the characters @ and : stand for
themselves.  Nearly all URI schemes currently in use are server-based.  An
authority component that does not parse in this way is considered to be
registry-based.
 The path component of a hierarchical URI is itself said to be absolute if it begins with a slash character ('/'); otherwise it is relative. The path of a hierarchical URI that is either absolute or specifies an authority is always absolute. 
 All told, then, a URI instance has the following nine components:

Describes the components of a URI:scheme,scheme-specific-part,authority,user-info,host,port,path,query,fragment

Component
Type


scheme
String
scheme-specific-part
String
authority
String
user-info
String
host
String
port
int
path
String
query
String
fragment
String


In a given instance any particular component is either undefined or
defined with a distinct value. Undefined string components are represented by null, while undefined integer components are represented by -1. A string component may be defined to have the empty string as its value; this is not equivalent to that component being undefined. 
 Whether a particular component is or is not defined in an instance
depends upon the type of the URI being represented.  An absolute URI has a
scheme component.  An opaque URI has a scheme, a scheme-specific part, and
possibly a fragment, but has no other components.  A hierarchical URI always
has a path (though it may be empty) and a scheme-specific-part (which at
least contains the path), and may have any of the other components.  If the
authority component is present and is server-based then the host component
will be defined and the user-information and port components may be defined.
 Operations on URI instances 
The key operations supported by this class are those of
normalization, resolution, and relativization.
 Normalization is the process of removing unnecessary "." and ".." segments from the path component of a hierarchical URI. Each "." segment is simply removed. A ".." segment is removed only if it is preceded by a non-".." segment. Normalization has no effect upon opaque URIs. 
 Resolution is the process of resolving one URI against another,
base URI.  The resulting URI is constructed from components of both
URIs in the manner specified by RFC 2396, taking components from the
base URI for those not specified in the original.  For hierarchical URIs,
the path of the original is resolved against the path of the base and then
normalized.  The result, for example, of resolving
 sample/a/index.html#28 (1) 
 against the base URI http://example.com/languages/java/ is the result URI 
 http://example.com/languages/java/sample/a/index.html#28 
Resolving the relative URI
 ../../demo/b/index.html (2) 
against this result yields, in turn,
 http://example.com/languages/java/demo/b/index.html 
 Resolution of both absolute and relative URIs, and of both absolute and relative paths in the case of hierarchical URIs, is supported. Resolving the URI file:///~calendar against any other URI simply yields the original URI, since it is absolute. Resolving the relative URI (2) above against the relative base URI (1) yields the normalized, but still relative, URI 
 demo/b/index.html 
 Relativization, finally, is the inverse of resolution: For any
two normalized URIs u and v,

  u.relativize(u.resolve(v)).equals(v) and

  u.resolve(u.relativize(v)).equals(v) .


This operation is often useful when constructing a document containing URIs
that must be made relative to the base URI of the document wherever
possible.  For example, relativizing the URI
 http://example.com/languages/java/sample/a/index.html#28 
against the base URI
 http://example.com/languages/java/ 
 yields the relative URI sample/a/index.html#28. 
 Character categories 
RFC 2396 specifies precisely which characters are permitted in the
various components of a URI reference.  The following categories, most of
which are taken from that specification, are used below to describe these
constraints:

Describes categories alpha,digit,alphanum,unreserved,punct,reserved,escaped,and other
  

  
Category
Description
  
  

  
alpha
      
The US-ASCII alphabetic characters, 'A' through 'Z' and 'a' through 'z'
  
digit
      
The US-ASCII decimal digit characters, '0' through '9'
  
alphanum
      
All alpha and digit characters
  
unreserved
      
All alphanum characters together with those in the string "_-!.~'()*"
  
punct
      
The characters in the string ",;:$&+="
  
reserved
      
All punct characters together with those in the string "?/[]@"
  
escaped
      
Escaped octets, that is, triplets consisting of the percent character ('%') followed by two hexadecimal digits ('0'-'9', 'A'-'F', and 'a'-'f')
  
other
      
The Unicode characters that are not in the US-ASCII character set, are not control characters (according to the Character.isISOControl method), and are not space characters (according to the Character.isSpaceChar method) (Deviation from RFC 2396, which is
          limited to US-ASCII)


 The set of all legal URI characters consists of
the unreserved, reserved, escaped, and other
characters.
 Escaped octets, quotation, encoding, and decoding 
RFC 2396 allows escaped octets to appear in the user-info, path, query, and
fragment components.  Escaping serves two purposes in URIs:

  
 To encode non-US-ASCII characters when a URI is required to
  conform strictly to RFC 2396 by not containing any other
  characters.  
  
 To quote characters that are otherwise illegal in a
  component.  The user-info, path, query, and fragment components differ
  slightly in terms of which characters are considered legal and illegal.
  

These purposes are served in this class by three related operations:

  
 A character is encoded by replacing it with the sequence of escaped octets that represent that character in the UTF-8 character set. The Euro currency symbol ('\u005Cu20AC'), for example, is encoded as "%E2%82%AC". (Deviation from
  RFC 2396, which does not specify any particular character
  set.) 
  
 An illegal character is quoted simply by encoding it. The space character, for example, is quoted by replacing it with "%20". UTF-8 contains US-ASCII, hence for US-ASCII characters this transformation has exactly the effect required by RFC 2396. 
  

  A sequence of escaped octets is decoded by
  replacing it with the sequence of characters that it represents in the
  UTF-8 character set.  UTF-8 contains US-ASCII, hence decoding has the
  effect of de-quoting any quoted US-ASCII characters as well as that of
  decoding any encoded non-US-ASCII characters.  If a decoding error occurs when decoding the escaped octets then the erroneous octets are replaced by '\u005CuFFFD', the Unicode replacement character. 

These operations are exposed in the constructors and methods of this class
as follows:

  
 The single-argument
  constructor requires any illegal characters in its argument to be quoted and preserves any escaped octets and other characters that
  are present.  
  
 The 
  multi-argument constructors quote illegal characters as required by the components in which they appear. The percent character ('%') is always quoted by these constructors. Any other
  characters are preserved.  
  
 The getRawUserInfo, 
  getRawPath, getRawQuery, 
  getRawFragment, getRawAuthority, and getRawSchemeSpecificPart methods return the values of their corresponding components in raw form, without interpreting any escaped octets. The strings returned by these methods may contain both escaped octets and other characters, and will not contain any
  illegal characters.  
  
 The getUserInfo, 
  getPath, getQuery, 
  getFragment, getAuthority, and getSchemeSpecificPart methods decode any escaped octets in their corresponding components. The strings returned by these methods may contain both other characters and illegal characters,
  and will not contain any escaped octets.  
  
 The toString method returns a URI string with all necessary quotation but which may contain other characters.
  
  
 The toASCIIString method returns a fully quoted and encoded URI string that does not contain any other
  characters.  

 Identities 
For any URI u, it is always the case that
 new URI(u.toString()).equals(u) . 
For any URI u that does not contain redundant syntax such as two slashes before an empty authority (as in file:///tmp/ ) or a colon following a host name but no port (as in http://java.sun.com: ), and that does not encode characters except those that must be quoted, the following identities also hold: 
    new URI(u.getScheme(),
            u.getSchemeSpecificPart(),
            u.getFragment())
    .equals(u)
in all cases,
    new URI(u.getScheme(),
            u.getAuthority(),
            u.getPath(), u.getQuery(),
            u.getFragment())
    .equals(u)
if u is hierarchical, and
    new URI(u.getScheme(),
            u.getUserInfo(), u.getHost(), u.getPort(),
            u.getPath(), u.getQuery(),
            u.getFragment())
    .equals(u)
if u is hierarchical and has either no authority or a server-based
authority.
 URIs, URLs, and URNs 
A URI is a uniform resource identifier while a URL is a uniform
resource locator.  Hence every URL is a URI, abstractly speaking, but
not every URI is a URL.  This is because there is another subcategory of
URIs, uniform resource names (URNs), which name resources but do not specify how to locate them. The mailto, news, and isbn URIs shown above are examples of URNs. 
 The conceptual distinction between URIs and URLs is reflected in the differences between this class and the URL class. 
 An instance of this class represents a URI reference in the syntactic
sense defined by RFC 2396.  A URI may be either absolute or relative.
A URI string is parsed according to the generic syntax without regard to the
scheme, if any, that it specifies.  No lookup of the host, if any, is
performed, and no scheme-dependent stream handler is constructed.  Equality,
hashing, and comparison are defined strictly in terms of the character
content of the instance.  In other words, a URI instance is little more than
a structured string that supports the syntactic, scheme-independent
operations of comparison, normalization, resolution, and relativization.
 An instance of the URL class, by contrast, represents the syntactic components of a URL together with some of the information required to access the resource that it describes. A URL must be absolute, that is, it must always specify a scheme. A URL string is parsed according to its scheme. A stream handler is always established for a URL, and in fact it is impossible to create a URL instance for a scheme for which no handler is available. Equality and hashing depend upon both the scheme and the Internet address of the host, if any; comparison is not defined. In other words, a URL is a structured string that supports the syntactic operation of resolution as well as the network I/O operations of looking up the host and opening a connection to the specified resource. 
Author:
Mark Reinhold
See Also:
RFC 2279: UTF-8, a
 * transformation format of ISO 10646, 
RFC 2373: IPv6 Addressing
Architecture, 
RFC 2396: Uniform
Resource Identifiers (URI): Generic Syntax, 
RFC 2732: Format for
Literal IPv6 Addresses in URLs, 
URISyntaxException
Since:
1.4/**
 * Represents a Uniform Resource Identifier (URI) reference.
 *
 * <p> Aside from some minor deviations noted below, an instance of this
 * class represents a URI reference as defined by
 * <a href="http://www.ietf.org/rfc/rfc2396.txt"><i>RFC&nbsp;2396: Uniform
 * Resource Identifiers (URI): Generic Syntax</i></a>, amended by <a
 * href="http://www.ietf.org/rfc/rfc2732.txt"><i>RFC&nbsp;2732: Format for
 * Literal IPv6 Addresses in URLs</i></a>. The Literal IPv6 address format
 * also supports scope_ids. The syntax and usage of scope_ids is described
 * <a href="Inet6Address.html#scoped">here</a>.
 * This class provides constructors for creating URI instances from
 * their components or by parsing their string forms, methods for accessing the
 * various components of an instance, and methods for normalizing, resolving,
 * and relativizing URI instances.  Instances of this class are immutable.
 *
 *
 * <h3> URI syntax and components </h3>
 *
 * At the highest level a URI reference (hereinafter simply "URI") in string
 * form has the syntax
 *
 * <blockquote>
 * [<i>scheme</i><b>{@code :}</b>]<i>scheme-specific-part</i>[<b>{@code #}</b><i>fragment</i>]
 * </blockquote>
 *
 * where square brackets [...] delineate optional components and the characters
 * <b>{@code :}</b> and <b>{@code #}</b> stand for themselves.
 *
 * <p> An <i>absolute</i> URI specifies a scheme; a URI that is not absolute is
 * said to be <i>relative</i>.  URIs are also classified according to whether
 * they are <i>opaque</i> or <i>hierarchical</i>.
 *
 * <p> An <i>opaque</i> URI is an absolute URI whose scheme-specific part does
 * not begin with a slash character ({@code '/'}).  Opaque URIs are not
 * subject to further parsing.  Some examples of opaque URIs are:
 *
 * <blockquote><ul style="list-style-type:none">
 * <li>{@code mailto:java-net@java.sun.com}</li>
 * <li>{@code news:comp.lang.java}</li>
 * <li>{@code urn:isbn:096139210x}</li>
 * </ul></blockquote>
 *
 * <p> A <i>hierarchical</i> URI is either an absolute URI whose
 * scheme-specific part begins with a slash character, or a relative URI, that
 * is, a URI that does not specify a scheme.  Some examples of hierarchical
 * URIs are:
 *
 * <blockquote>
 * {@code http://example.com/languages/java/}<br>
 * {@code sample/a/index.html#28}<br>
 * {@code ../../demo/b/index.html}<br>
 * {@code file:///~/calendar}
 * </blockquote>
 *
 * <p> A hierarchical URI is subject to further parsing according to the syntax
 *
 * <blockquote>
 * [<i>scheme</i><b>{@code :}</b>][<b>{@code //}</b><i>authority</i>][<i>path</i>][<b>{@code ?}</b><i>query</i>][<b>{@code #}</b><i>fragment</i>]
 * </blockquote>
 *
 * where the characters <b>{@code :}</b>, <b>{@code /}</b>,
 * <b>{@code ?}</b>, and <b>{@code #}</b> stand for themselves.  The
 * scheme-specific part of a hierarchical URI consists of the characters
 * between the scheme and fragment components.
 *
 * <p> The authority component of a hierarchical URI is, if specified, either
 * <i>server-based</i> or <i>registry-based</i>.  A server-based authority
 * parses according to the familiar syntax
 *
 * <blockquote>
 * [<i>user-info</i><b>{@code @}</b>]<i>host</i>[<b>{@code :}</b><i>port</i>]
 * </blockquote>
 *
 * where the characters <b>{@code @}</b> and <b>{@code :}</b> stand for
 * themselves.  Nearly all URI schemes currently in use are server-based.  An
 * authority component that does not parse in this way is considered to be
 * registry-based.
 *
 * <p> The path component of a hierarchical URI is itself said to be absolute
 * if it begins with a slash character ({@code '/'}); otherwise it is
 * relative.  The path of a hierarchical URI that is either absolute or
 * specifies an authority is always absolute.
 *
 * <p> All told, then, a URI instance has the following nine components:
 *
 * <table class="striped" style="margin-left:2em">
 * <caption style="display:none">Describes the components of a URI:scheme,scheme-specific-part,authority,user-info,host,port,path,query,fragment</caption>
 * <thead>
 * <tr><th scope="col">Component</th><th scope="col">Type</th></tr>
 * </thead>
 * <tbody style="text-align:left">
 * <tr><th scope="row">scheme</th><td>{@code String}</td></tr>
 * <tr><th scope="row">scheme-specific-part</th><td>{@code String}</td></tr>
 * <tr><th scope="row">authority</th><td>{@code String}</td></tr>
 * <tr><th scope="row">user-info</th><td>{@code String}</td></tr>
 * <tr><th scope="row">host</th><td>{@code String}</td></tr>
 * <tr><th scope="row">port</th><td>{@code int}</td></tr>
 * <tr><th scope="row">path</th><td>{@code String}</td></tr>
 * <tr><th scope="row">query</th><td>{@code String}</td></tr>
 * <tr><th scope="row">fragment</th><td>{@code String}</td></tr>
 * </tbody>
 * </table>
 *
 * In a given instance any particular component is either <i>undefined</i> or
 * <i>defined</i> with a distinct value.  Undefined string components are
 * represented by {@code null}, while undefined integer components are
 * represented by {@code -1}.  A string component may be defined to have the
 * empty string as its value; this is not equivalent to that component being
 * undefined.
 *
 * <p> Whether a particular component is or is not defined in an instance
 * depends upon the type of the URI being represented.  An absolute URI has a
 * scheme component.  An opaque URI has a scheme, a scheme-specific part, and
 * possibly a fragment, but has no other components.  A hierarchical URI always
 * has a path (though it may be empty) and a scheme-specific-part (which at
 * least contains the path), and may have any of the other components.  If the
 * authority component is present and is server-based then the host component
 * will be defined and the user-information and port components may be defined.
 *
 *
 * <h4> Operations on URI instances </h4>
 *
 * The key operations supported by this class are those of
 * <i>normalization</i>, <i>resolution</i>, and <i>relativization</i>.
 *
 * <p> <i>Normalization</i> is the process of removing unnecessary {@code "."}
 * and {@code ".."} segments from the path component of a hierarchical URI.
 * Each {@code "."} segment is simply removed.  A {@code ".."} segment is
 * removed only if it is preceded by a non-{@code ".."} segment.
 * Normalization has no effect upon opaque URIs.
 *
 * <p> <i>Resolution</i> is the process of resolving one URI against another,
 * <i>base</i> URI.  The resulting URI is constructed from components of both
 * URIs in the manner specified by RFC&nbsp;2396, taking components from the
 * base URI for those not specified in the original.  For hierarchical URIs,
 * the path of the original is resolved against the path of the base and then
 * normalized.  The result, for example, of resolving
 *
 * <blockquote>
 * {@code sample/a/index.html#28}
 * &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
 * &nbsp;&nbsp;&nbsp;&nbsp;(1)
 * </blockquote>
 *
 * against the base URI {@code http://example.com/languages/java/} is the result
 * URI
 *
 * <blockquote>
 * {@code http://example.com/languages/java/sample/a/index.html#28}
 * </blockquote>
 *
 * Resolving the relative URI
 *
 * <blockquote>
 * {@code ../../demo/b/index.html}&nbsp;&nbsp;&nbsp;&nbsp;(2)
 * </blockquote>
 *
 * against this result yields, in turn,
 *
 * <blockquote>
 * {@code http://example.com/languages/java/demo/b/index.html}
 * </blockquote>
 *
 * Resolution of both absolute and relative URIs, and of both absolute and
 * relative paths in the case of hierarchical URIs, is supported.  Resolving
 * the URI {@code file:///~calendar} against any other URI simply yields the
 * original URI, since it is absolute.  Resolving the relative URI (2) above
 * against the relative base URI (1) yields the normalized, but still relative,
 * URI
 *
 * <blockquote>
 * {@code demo/b/index.html}
 * </blockquote>
 *
 * <p> <i>Relativization</i>, finally, is the inverse of resolution: For any
 * two normalized URIs <i>u</i> and&nbsp;<i>v</i>,
 *
 * <blockquote>
 *   <i>u</i>{@code .relativize(}<i>u</i>{@code .resolve(}<i>v</i>{@code )).equals(}<i>v</i>{@code )}&nbsp;&nbsp;and<br>
 *   <i>u</i>{@code .resolve(}<i>u</i>{@code .relativize(}<i>v</i>{@code )).equals(}<i>v</i>{@code )}&nbsp;&nbsp;.<br>
 * </blockquote>
 *
 * This operation is often useful when constructing a document containing URIs
 * that must be made relative to the base URI of the document wherever
 * possible.  For example, relativizing the URI
 *
 * <blockquote>
 * {@code http://example.com/languages/java/sample/a/index.html#28}
 * </blockquote>
 *
 * against the base URI
 *
 * <blockquote>
 * {@code http://example.com/languages/java/}
 * </blockquote>
 *
 * yields the relative URI {@code sample/a/index.html#28}.
 *
 *
 * <h4> Character categories </h4>
 *
 * RFC&nbsp;2396 specifies precisely which characters are permitted in the
 * various components of a URI reference.  The following categories, most of
 * which are taken from that specification, are used below to describe these
 * constraints:
 *
 * <table class="striped" style="margin-left:2em">
 * <caption style="display:none">Describes categories alpha,digit,alphanum,unreserved,punct,reserved,escaped,and other</caption>
 *   <thead>
 *   <tr><th scope="col">Category</th><th scope="col">Description</th></tr>
 *   </thead>
 *   <tbody style="text-align:left">
 *   <tr><th scope="row" style="vertical-align:top">alpha</th>
 *       <td>The US-ASCII alphabetic characters,
 *        {@code 'A'}&nbsp;through&nbsp;{@code 'Z'}
 *        and {@code 'a'}&nbsp;through&nbsp;{@code 'z'}</td></tr>
 *   <tr><th scope="row" style="vertical-align:top">digit</th>
 *       <td>The US-ASCII decimal digit characters,
 *       {@code '0'}&nbsp;through&nbsp;{@code '9'}</td></tr>
 *   <tr><th scope="row" style="vertical-align:top">alphanum</th>
 *       <td>All <i>alpha</i> and <i>digit</i> characters</td></tr>
 *   <tr><th scope="row" style="vertical-align:top">unreserved</th>
 *       <td>All <i>alphanum</i> characters together with those in the string
 *        {@code "_-!.~'()*"}</td></tr>
 *   <tr><th scope="row" style="vertical-align:top">punct</th>
 *       <td>The characters in the string {@code ",;:$&+="}</td></tr>
 *   <tr><th scope="row" style="vertical-align:top">reserved</th>
 *       <td>All <i>punct</i> characters together with those in the string
 *        {@code "?/[]@"}</td></tr>
 *   <tr><th scope="row" style="vertical-align:top">escaped</th>
 *       <td>Escaped octets, that is, triplets consisting of the percent
 *           character ({@code '%'}) followed by two hexadecimal digits
 *           ({@code '0'}-{@code '9'}, {@code 'A'}-{@code 'F'}, and
 *           {@code 'a'}-{@code 'f'})</td></tr>
 *   <tr><th scope="row" style="vertical-align:top">other</th>
 *       <td>The Unicode characters that are not in the US-ASCII character set,
 *           are not control characters (according to the {@link
 *           java.lang.Character#isISOControl(char) Character.isISOControl}
 *           method), and are not space characters (according to the {@link
 *           java.lang.Character#isSpaceChar(char) Character.isSpaceChar}
 *           method)&nbsp;&nbsp;<i>(<b>Deviation from RFC 2396</b>, which is
 *           limited to US-ASCII)</i></td></tr>
 * </tbody>
 * </table>
 *
 * <p><a id="legal-chars"></a> The set of all legal URI characters consists of
 * the <i>unreserved</i>, <i>reserved</i>, <i>escaped</i>, and <i>other</i>
 * characters.
 *
 *
 * <h4> Escaped octets, quotation, encoding, and decoding </h4>
 *
 * RFC 2396 allows escaped octets to appear in the user-info, path, query, and
 * fragment components.  Escaping serves two purposes in URIs:
 *
 * <ul>
 *
 *   <li><p> To <i>encode</i> non-US-ASCII characters when a URI is required to
 *   conform strictly to RFC&nbsp;2396 by not containing any <i>other</i>
 *   characters.  </p></li>
 *
 *   <li><p> To <i>quote</i> characters that are otherwise illegal in a
 *   component.  The user-info, path, query, and fragment components differ
 *   slightly in terms of which characters are considered legal and illegal.
 *   </p></li>
 *
 * </ul>
 *
 * These purposes are served in this class by three related operations:
 *
 * <ul>
 *
 *   <li><p><a id="encode"></a> A character is <i>encoded</i> by replacing it
 *   with the sequence of escaped octets that represent that character in the
 *   UTF-8 character set.  The Euro currency symbol ({@code '\u005Cu20AC'}),
 *   for example, is encoded as {@code "%E2%82%AC"}.  <i>(<b>Deviation from
 *   RFC&nbsp;2396</b>, which does not specify any particular character
 *   set.)</i> </p></li>
 *
 *   <li><p><a id="quote"></a> An illegal character is <i>quoted</i> simply by
 *   encoding it.  The space character, for example, is quoted by replacing it
 *   with {@code "%20"}.  UTF-8 contains US-ASCII, hence for US-ASCII
 *   characters this transformation has exactly the effect required by
 *   RFC&nbsp;2396. </p></li>
 *
 *   <li><p><a id="decode"></a>
 *   A sequence of escaped octets is <i>decoded</i> by
 *   replacing it with the sequence of characters that it represents in the
 *   UTF-8 character set.  UTF-8 contains US-ASCII, hence decoding has the
 *   effect of de-quoting any quoted US-ASCII characters as well as that of
 *   decoding any encoded non-US-ASCII characters.  If a <a
 *   href="../nio/charset/CharsetDecoder.html#ce">decoding error</a> occurs
 *   when decoding the escaped octets then the erroneous octets are replaced by
 *   {@code '\u005CuFFFD'}, the Unicode replacement character.  </p></li>
 *
 * </ul>
 *
 * These operations are exposed in the constructors and methods of this class
 * as follows:
 *
 * <ul>
 *
 *   <li><p> The {@linkplain #URI(java.lang.String) single-argument
 *   constructor} requires any illegal characters in its argument to be
 *   quoted and preserves any escaped octets and <i>other</i> characters that
 *   are present.  </p></li>
 *
 *   <li><p> The {@linkplain
 *   #URI(java.lang.String,java.lang.String,java.lang.String,int,java.lang.String,java.lang.String,java.lang.String)
 *   multi-argument constructors} quote illegal characters as
 *   required by the components in which they appear.  The percent character
 *   ({@code '%'}) is always quoted by these constructors.  Any <i>other</i>
 *   characters are preserved.  </p></li>
 *
 *   <li><p> The {@link #getRawUserInfo() getRawUserInfo}, {@link #getRawPath()
 *   getRawPath}, {@link #getRawQuery() getRawQuery}, {@link #getRawFragment()
 *   getRawFragment}, {@link #getRawAuthority() getRawAuthority}, and {@link
 *   #getRawSchemeSpecificPart() getRawSchemeSpecificPart} methods return the
 *   values of their corresponding components in raw form, without interpreting
 *   any escaped octets.  The strings returned by these methods may contain
 *   both escaped octets and <i>other</i> characters, and will not contain any
 *   illegal characters.  </p></li>
 *
 *   <li><p> The {@link #getUserInfo() getUserInfo}, {@link #getPath()
 *   getPath}, {@link #getQuery() getQuery}, {@link #getFragment()
 *   getFragment}, {@link #getAuthority() getAuthority}, and {@link
 *   #getSchemeSpecificPart() getSchemeSpecificPart} methods decode any escaped
 *   octets in their corresponding components.  The strings returned by these
 *   methods may contain both <i>other</i> characters and illegal characters,
 *   and will not contain any escaped octets.  </p></li>
 *
 *   <li><p> The {@link #toString() toString} method returns a URI string with
 *   all necessary quotation but which may contain <i>other</i> characters.
 *   </p></li>
 *
 *   <li><p> The {@link #toASCIIString() toASCIIString} method returns a fully
 *   quoted and encoded URI string that does not contain any <i>other</i>
 *   characters.  </p></li>
 *
 * </ul>
 *
 *
 * <h4> Identities </h4>
 *
 * For any URI <i>u</i>, it is always the case that
 *
 * <blockquote>
 * {@code new URI(}<i>u</i>{@code .toString()).equals(}<i>u</i>{@code )}&nbsp;.
 * </blockquote>
 *
 * For any URI <i>u</i> that does not contain redundant syntax such as two
 * slashes before an empty authority (as in {@code file:///tmp/}&nbsp;) or a
 * colon following a host name but no port (as in
 * {@code http://java.sun.com:}&nbsp;), and that does not encode characters
 * except those that must be quoted, the following identities also hold:
 * <pre>
 *     new URI(<i>u</i>.getScheme(),
 *             <i>u</i>.getSchemeSpecificPart(),
 *             <i>u</i>.getFragment())
 *     .equals(<i>u</i>)</pre>
 * in all cases,
 * <pre>
 *     new URI(<i>u</i>.getScheme(),
 *             <i>u</i>.getAuthority(),
 *             <i>u</i>.getPath(), <i>u</i>.getQuery(),
 *             <i>u</i>.getFragment())
 *     .equals(<i>u</i>)</pre>
 * if <i>u</i> is hierarchical, and
 * <pre>
 *     new URI(<i>u</i>.getScheme(),
 *             <i>u</i>.getUserInfo(), <i>u</i>.getHost(), <i>u</i>.getPort(),
 *             <i>u</i>.getPath(), <i>u</i>.getQuery(),
 *             <i>u</i>.getFragment())
 *     .equals(<i>u</i>)</pre>
 * if <i>u</i> is hierarchical and has either no authority or a server-based
 * authority.
 *
 *
 * <h4> URIs, URLs, and URNs </h4>
 *
 * A URI is a uniform resource <i>identifier</i> while a URL is a uniform
 * resource <i>locator</i>.  Hence every URL is a URI, abstractly speaking, but
 * not every URI is a URL.  This is because there is another subcategory of
 * URIs, uniform resource <i>names</i> (URNs), which name resources but do not
 * specify how to locate them.  The {@code mailto}, {@code news}, and
 * {@code isbn} URIs shown above are examples of URNs.
 *
 * <p> The conceptual distinction between URIs and URLs is reflected in the
 * differences between this class and the {@link URL} class.
 *
 * <p> An instance of this class represents a URI reference in the syntactic
 * sense defined by RFC&nbsp;2396.  A URI may be either absolute or relative.
 * A URI string is parsed according to the generic syntax without regard to the
 * scheme, if any, that it specifies.  No lookup of the host, if any, is
 * performed, and no scheme-dependent stream handler is constructed.  Equality,
 * hashing, and comparison are defined strictly in terms of the character
 * content of the instance.  In other words, a URI instance is little more than
 * a structured string that supports the syntactic, scheme-independent
 * operations of comparison, normalization, resolution, and relativization.
 *
 * <p> An instance of the {@link URL} class, by contrast, represents the
 * syntactic components of a URL together with some of the information required
 * to access the resource that it describes.  A URL must be absolute, that is,
 * it must always specify a scheme.  A URL string is parsed according to its
 * scheme.  A stream handler is always established for a URL, and in fact it is
 * impossible to create a URL instance for a scheme for which no handler is
 * available.  Equality and hashing depend upon both the scheme and the
 * Internet address of the host, if any; comparison is not defined.  In other
 * words, a URL is a structured string that supports the syntactic operation of
 * resolution as well as the network I/O operations of looking up the host and
 * opening a connection to the specified resource.
 *
 *
 * @author Mark Reinhold
 * @since 1.4
 *
 * @see <a href="http://www.ietf.org/rfc/rfc2279.txt"><i>RFC&nbsp;2279: UTF-8, a
 * transformation format of ISO 10646</i></a>, <br><a
 * href="http://www.ietf.org/rfc/rfc2373.txt"><i>RFC&nbsp;2373: IPv6 Addressing
 * Architecture</i></a>, <br><a
 * href="http://www.ietf.org/rfc/rfc2396.txt"><i>RFC&nbsp;2396: Uniform
 * Resource Identifiers (URI): Generic Syntax</i></a>, <br><a
 * href="http://www.ietf.org/rfc/rfc2732.txt"><i>RFC&nbsp;2732: Format for
 * Literal IPv6 Addresses in URLs</i></a>, <br><a
 * href="URISyntaxException.html">URISyntaxException</a>
 */

public final class URI
    implements Comparable<URI>, Serializable
{

    // Note: Comments containing the word "ASSERT" indicate places where a
    // throw of an InternalError should be replaced by an appropriate assertion
    // statement once asserts are enabled in the build.

    static final long serialVersionUID = -6052424284110960213L;


    // -- Properties and components of this instance --

    // Components of all URIs: [<scheme>:]<scheme-specific-part>[#<fragment>]
    private transient String scheme;            // null ==> relative URI
    private transient String fragment;

    // Hierarchical URI components: [//<authority>]<path>[?<query>]
    private transient String authority;         // Registry or server

    // Server-based authority: [<userInfo>@]<host>[:<port>]
    private transient String userInfo;
    private transient String host;              // null ==> registry-based
    private transient int port = -1;            // -1 ==> undefined

    // Remaining components of hierarchical URIs
    private transient String path;              // null ==> opaque
    private transient String query;

    // The remaining fields may be computed on demand, which is safe even in
    // the face of multiple threads racing to initialize them
    private transient String schemeSpecificPart;
    private transient int hash;        // Zero ==> undefined

    private transient String decodedUserInfo;
    private transient String decodedAuthority;
    private transient String decodedPath;
    private transient String decodedQuery;
    private transient String decodedFragment;
    private transient String decodedSchemeSpecificPart;

    
The string form of this URI.
@serial
/**
     * The string form of this URI.
     *
     * @serial
     */
    private volatile String string;             // The only serializable field



    // -- Constructors and factories --

    private URI() { }                           // Used internally

    
Constructs a URI by parsing the given string.
 This constructor parses the given string exactly as specified by the
grammar in RFC 2396,
Appendix A, except for the following deviations: 

  
 An empty authority component is permitted as long as it is followed by a non-empty path, a query component, or a fragment component. This allows the parsing of URIs such as "file:///foo/bar", which seems to be the intent of RFC 2396 although the grammar does not permit it. If the authority component is empty then the user-information, host, and port components are undefined. 
  
 Empty relative paths are permitted; this seems to be the intent of RFC 2396 although the grammar does not permit it. The primary consequence of this deviation is that a standalone fragment such as "#foo" parses as a relative URI with an empty path and the given fragment, and can be usefully resolved against a base URI.
  
 IPv4 addresses in host components are parsed rigorously, as
  specified by RFC 2732: Each
  element of a dotted-quad address must contain no more than three
  decimal digits.  Each element is further constrained to have a value
  no greater than 255. 
  
 
 Hostnames in host components that comprise only a single
  domain label are permitted to start with an alphanum
  character. This seems to be the intent of RFC 2396 section 3.2.2 although the grammar does not permit it. The consequence of this deviation is that the authority component of a hierarchical URI such as s://123, will parse as a server-based authority. 
  
 IPv6 addresses are permitted for the host component. An IPv6 address must be enclosed in square brackets ('[' and ']') as specified by RFC 2732.  The
  IPv6 address itself must parse according to RFC 2373.  IPv6
  addresses are further constrained to describe no more than sixteen
  bytes of address information, a constraint implicit in RFC 2373
  but not expressible in the grammar. 
  
 Characters in the other category are permitted wherever
  RFC 2396 permits escaped octets, that is, in the
  user-information, path, query, and fragment components, as well as in
  the authority component if the authority is registry-based.  This
  allows URIs to contain Unicode characters beyond those in the US-ASCII
  character set. 

Params:
str –   The string to be parsed into a URI
Throws:
NullPointerException –  If str is null
URISyntaxException – 
         If the given string violates RFC 2396, as augmented
         by the above deviations/**
     * Constructs a URI by parsing the given string.
     *
     * <p> This constructor parses the given string exactly as specified by the
     * grammar in <a
     * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,
     * Appendix&nbsp;A, <b><i>except for the following deviations:</i></b> </p>
     *
     * <ul>
     *
     *   <li><p> An empty authority component is permitted as long as it is
     *   followed by a non-empty path, a query component, or a fragment
     *   component.  This allows the parsing of URIs such as
     *   {@code "file:///foo/bar"}, which seems to be the intent of
     *   RFC&nbsp;2396 although the grammar does not permit it.  If the
     *   authority component is empty then the user-information, host, and port
     *   components are undefined. </p></li>
     *
     *   <li><p> Empty relative paths are permitted; this seems to be the
     *   intent of RFC&nbsp;2396 although the grammar does not permit it.  The
     *   primary consequence of this deviation is that a standalone fragment
     *   such as {@code "#foo"} parses as a relative URI with an empty path
     *   and the given fragment, and can be usefully <a
     *   href="#resolve-frag">resolved</a> against a base URI.
     *
     *   <li><p> IPv4 addresses in host components are parsed rigorously, as
     *   specified by <a
     *   href="http://www.ietf.org/rfc/rfc2732.txt">RFC&nbsp;2732</a>: Each
     *   element of a dotted-quad address must contain no more than three
     *   decimal digits.  Each element is further constrained to have a value
     *   no greater than 255. </p></li>
     *
     *   <li> <p> Hostnames in host components that comprise only a single
     *   domain label are permitted to start with an <i>alphanum</i>
     *   character. This seems to be the intent of <a
     *   href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>
     *   section&nbsp;3.2.2 although the grammar does not permit it. The
     *   consequence of this deviation is that the authority component of a
     *   hierarchical URI such as {@code s://123}, will parse as a server-based
     *   authority. </p></li>
     *
     *   <li><p> IPv6 addresses are permitted for the host component.  An IPv6
     *   address must be enclosed in square brackets ({@code '['} and
     *   {@code ']'}) as specified by <a
     *   href="http://www.ietf.org/rfc/rfc2732.txt">RFC&nbsp;2732</a>.  The
     *   IPv6 address itself must parse according to <a
     *   href="http://www.ietf.org/rfc/rfc2373.txt">RFC&nbsp;2373</a>.  IPv6
     *   addresses are further constrained to describe no more than sixteen
     *   bytes of address information, a constraint implicit in RFC&nbsp;2373
     *   but not expressible in the grammar. </p></li>
     *
     *   <li><p> Characters in the <i>other</i> category are permitted wherever
     *   RFC&nbsp;2396 permits <i>escaped</i> octets, that is, in the
     *   user-information, path, query, and fragment components, as well as in
     *   the authority component if the authority is registry-based.  This
     *   allows URIs to contain Unicode characters beyond those in the US-ASCII
     *   character set. </p></li>
     *
     * </ul>
     *
     * @param  str   The string to be parsed into a URI
     *
     * @throws  NullPointerException
     *          If {@code str} is {@code null}
     *
     * @throws  URISyntaxException
     *          If the given string violates RFC&nbsp;2396, as augmented
     *          by the above deviations
     */
    public URI(String str) throws URISyntaxException {
        new Parser(str).parse(false);
    }

    
Constructs a hierarchical URI from the given components.
 If a scheme is given then the path, if also given, must either be empty or begin with a slash character ('/'). Otherwise a component of the new URI may be left undefined by passing null for the corresponding parameter or, in the case of the port parameter, by passing -1. 
 This constructor first builds a URI string from the given components
according to the rules specified in RFC 2396,
section 5.2, step 7: 

  
 Initially, the result string is empty. 
  
 If a scheme is given then it is appended to the result, followed by a colon character (':'). 
  
 If user information, a host, or a port are given then the string "//" is appended. 
  
 If user information is given then it is appended, followed by a commercial-at character ('@'). Any character not in the unreserved, punct, escaped, or other
  categories is quoted.  
  
 If a host is given then it is appended. If the host is a literal IPv6 address but is not enclosed in square brackets ('[' and ']') then the square brackets are added. 
  
 If a port number is given then a colon character (':') is appended, followed by the port number in decimal. 
  
 If a path is given then it is appended.  Any character not in
  the unreserved, punct, escaped, or other categories, and not equal to the slash character ('/') or the commercial-at character ('@'), is quoted. 
  
 If a query is given then a question-mark character ('?') is appended, followed by the query. Any character that is not a legal URI character is quoted.
  
  
 Finally, if a fragment is given then a hash character ('#') is appended, followed by the fragment. Any character that is not a legal URI character is quoted. 

 The resulting URI string is then parsed as if by invoking the URI(String) constructor and then invoking the parseServerAuthority() method upon the result; this may cause a URISyntaxException to be thrown. 
Params:
scheme –    Scheme name
userInfo –  User name and authorization information
host –      Host name
port –      Port number
path –      Path
query –     Query
fragment –  Fragment
Throws:
URISyntaxException – 
        If both a scheme and a path are given but the path is relative,
        if the URI string constructed from the given components violates
        RFC 2396, or if the authority component of the string is
        present but cannot be parsed as a server-based authority/**
     * Constructs a hierarchical URI from the given components.
     *
     * <p> If a scheme is given then the path, if also given, must either be
     * empty or begin with a slash character ({@code '/'}).  Otherwise a
     * component of the new URI may be left undefined by passing {@code null}
     * for the corresponding parameter or, in the case of the {@code port}
     * parameter, by passing {@code -1}.
     *
     * <p> This constructor first builds a URI string from the given components
     * according to the rules specified in <a
     * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,
     * section&nbsp;5.2, step&nbsp;7: </p>
     *
     * <ol>
     *
     *   <li><p> Initially, the result string is empty. </p></li>
     *
     *   <li><p> If a scheme is given then it is appended to the result,
     *   followed by a colon character ({@code ':'}).  </p></li>
     *
     *   <li><p> If user information, a host, or a port are given then the
     *   string {@code "//"} is appended.  </p></li>
     *
     *   <li><p> If user information is given then it is appended, followed by
     *   a commercial-at character ({@code '@'}).  Any character not in the
     *   <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, or <i>other</i>
     *   categories is <a href="#quote">quoted</a>.  </p></li>
     *
     *   <li><p> If a host is given then it is appended.  If the host is a
     *   literal IPv6 address but is not enclosed in square brackets
     *   ({@code '['} and {@code ']'}) then the square brackets are added.
     *   </p></li>
     *
     *   <li><p> If a port number is given then a colon character
     *   ({@code ':'}) is appended, followed by the port number in decimal.
     *   </p></li>
     *
     *   <li><p> If a path is given then it is appended.  Any character not in
     *   the <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, or <i>other</i>
     *   categories, and not equal to the slash character ({@code '/'}) or the
     *   commercial-at character ({@code '@'}), is quoted.  </p></li>
     *
     *   <li><p> If a query is given then a question-mark character
     *   ({@code '?'}) is appended, followed by the query.  Any character that
     *   is not a <a href="#legal-chars">legal URI character</a> is quoted.
     *   </p></li>
     *
     *   <li><p> Finally, if a fragment is given then a hash character
     *   ({@code '#'}) is appended, followed by the fragment.  Any character
     *   that is not a legal URI character is quoted.  </p></li>
     *
     * </ol>
     *
     * <p> The resulting URI string is then parsed as if by invoking the {@link
     * #URI(String)} constructor and then invoking the {@link
     * #parseServerAuthority()} method upon the result; this may cause a {@link
     * URISyntaxException} to be thrown.  </p>
     *
     * @param   scheme    Scheme name
     * @param   userInfo  User name and authorization information
     * @param   host      Host name
     * @param   port      Port number
     * @param   path      Path
     * @param   query     Query
     * @param   fragment  Fragment
     *
     * @throws URISyntaxException
     *         If both a scheme and a path are given but the path is relative,
     *         if the URI string constructed from the given components violates
     *         RFC&nbsp;2396, or if the authority component of the string is
     *         present but cannot be parsed as a server-based authority
     */
    public URI(String scheme,
               String userInfo, String host, int port,
               String path, String query, String fragment)
        throws URISyntaxException
    {
        String s = toString(scheme, null,
                            null, userInfo, host, port,
                            path, query, fragment);
        checkPath(s, scheme, path);
        new Parser(s).parse(true);
    }

    
Constructs a hierarchical URI from the given components.
 If a scheme is given then the path, if also given, must either be empty or begin with a slash character ('/'). Otherwise a component of the new URI may be left undefined by passing null for the corresponding parameter. 
 This constructor first builds a URI string from the given components
according to the rules specified in RFC 2396,
section 5.2, step 7: 

  
 Initially, the result string is empty.  
  
 If a scheme is given then it is appended to the result, followed by a colon character (':'). 
  
 If an authority is given then the string "//" is appended, followed by the authority. If the authority contains a literal IPv6 address then the address must be enclosed in square brackets ('[' and ']'). Any character not in the unreserved, punct, escaped, or other categories, and not equal to the commercial-at character ('@'), is quoted.  
  
 If a path is given then it is appended.  Any character not in
  the unreserved, punct, escaped, or other categories, and not equal to the slash character ('/') or the commercial-at character ('@'), is quoted. 
  
 If a query is given then a question-mark character ('?') is appended, followed by the query. Any character that is not a legal URI character is quoted.
  
  
 Finally, if a fragment is given then a hash character ('#') is appended, followed by the fragment. Any character that is not a legal URI character is quoted. 

 The resulting URI string is then parsed as if by invoking the URI(String) constructor and then invoking the parseServerAuthority() method upon the result; this may cause a URISyntaxException to be thrown. 
Params:
scheme –     Scheme name
authority –  Authority
path –       Path
query –      Query
fragment –   Fragment
Throws:
URISyntaxException – 
        If both a scheme and a path are given but the path is relative,
        if the URI string constructed from the given components violates
        RFC 2396, or if the authority component of the string is
        present but cannot be parsed as a server-based authority/**
     * Constructs a hierarchical URI from the given components.
     *
     * <p> If a scheme is given then the path, if also given, must either be
     * empty or begin with a slash character ({@code '/'}).  Otherwise a
     * component of the new URI may be left undefined by passing {@code null}
     * for the corresponding parameter.
     *
     * <p> This constructor first builds a URI string from the given components
     * according to the rules specified in <a
     * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,
     * section&nbsp;5.2, step&nbsp;7: </p>
     *
     * <ol>
     *
     *   <li><p> Initially, the result string is empty.  </p></li>
     *
     *   <li><p> If a scheme is given then it is appended to the result,
     *   followed by a colon character ({@code ':'}).  </p></li>
     *
     *   <li><p> If an authority is given then the string {@code "//"} is
     *   appended, followed by the authority.  If the authority contains a
     *   literal IPv6 address then the address must be enclosed in square
     *   brackets ({@code '['} and {@code ']'}).  Any character not in the
     *   <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, or <i>other</i>
     *   categories, and not equal to the commercial-at character
     *   ({@code '@'}), is <a href="#quote">quoted</a>.  </p></li>
     *
     *   <li><p> If a path is given then it is appended.  Any character not in
     *   the <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, or <i>other</i>
     *   categories, and not equal to the slash character ({@code '/'}) or the
     *   commercial-at character ({@code '@'}), is quoted.  </p></li>
     *
     *   <li><p> If a query is given then a question-mark character
     *   ({@code '?'}) is appended, followed by the query.  Any character that
     *   is not a <a href="#legal-chars">legal URI character</a> is quoted.
     *   </p></li>
     *
     *   <li><p> Finally, if a fragment is given then a hash character
     *   ({@code '#'}) is appended, followed by the fragment.  Any character
     *   that is not a legal URI character is quoted.  </p></li>
     *
     * </ol>
     *
     * <p> The resulting URI string is then parsed as if by invoking the {@link
     * #URI(String)} constructor and then invoking the {@link
     * #parseServerAuthority()} method upon the result; this may cause a {@link
     * URISyntaxException} to be thrown.  </p>
     *
     * @param   scheme     Scheme name
     * @param   authority  Authority
     * @param   path       Path
     * @param   query      Query
     * @param   fragment   Fragment
     *
     * @throws URISyntaxException
     *         If both a scheme and a path are given but the path is relative,
     *         if the URI string constructed from the given components violates
     *         RFC&nbsp;2396, or if the authority component of the string is
     *         present but cannot be parsed as a server-based authority
     */
    public URI(String scheme,
               String authority,
               String path, String query, String fragment)
        throws URISyntaxException
    {
        String s = toString(scheme, null,
                            authority, null, null, -1,
                            path, query, fragment);
        checkPath(s, scheme, path);
        new Parser(s).parse(false);
    }

    
Constructs a hierarchical URI from the given components.
 A component may be left undefined by passing null. 
 This convenience constructor works as if by invoking the
seven-argument constructor as follows:
 new 
URI(scheme, null, host, -1, path, null, fragment); 
Params:
scheme –    Scheme name
host –      Host name
path –      Path
fragment –  Fragment
Throws:
URISyntaxException – 
         If the URI string constructed from the given components
         violates RFC 2396/**
     * Constructs a hierarchical URI from the given components.
     *
     * <p> A component may be left undefined by passing {@code null}.
     *
     * <p> This convenience constructor works as if by invoking the
     * seven-argument constructor as follows:
     *
     * <blockquote>
     * {@code new} {@link #URI(String, String, String, int, String, String, String)
     * URI}{@code (scheme, null, host, -1, path, null, fragment);}
     * </blockquote>
     *
     * @param   scheme    Scheme name
     * @param   host      Host name
     * @param   path      Path
     * @param   fragment  Fragment
     *
     * @throws  URISyntaxException
     *          If the URI string constructed from the given components
     *          violates RFC&nbsp;2396
     */
    public URI(String scheme, String host, String path, String fragment)
        throws URISyntaxException
    {
        this(scheme, null, host, -1, path, null, fragment);
    }

    
Constructs a URI from the given components.
 A component may be left undefined by passing null. 
 This constructor first builds a URI in string form using the given
components as follows:  

  
 Initially, the result string is empty.  
  
 If a scheme is given then it is appended to the result, followed by a colon character (':'). 
  
 If a scheme-specific part is given then it is appended.  Any
  character that is not a legal URI character
  is quoted.  
  
 Finally, if a fragment is given then a hash character ('#') is appended to the string, followed by the fragment. Any character that is not a legal URI character is quoted. 

 The resulting URI string is then parsed in order to create the new URI instance as if by invoking the URI(String) constructor; this may cause a URISyntaxException to be thrown. 
Params:
scheme –    Scheme name
ssp –       Scheme-specific part
fragment –  Fragment
Throws:
URISyntaxException – 
         If the URI string constructed from the given components
         violates RFC 2396/**
     * Constructs a URI from the given components.
     *
     * <p> A component may be left undefined by passing {@code null}.
     *
     * <p> This constructor first builds a URI in string form using the given
     * components as follows:  </p>
     *
     * <ol>
     *
     *   <li><p> Initially, the result string is empty.  </p></li>
     *
     *   <li><p> If a scheme is given then it is appended to the result,
     *   followed by a colon character ({@code ':'}).  </p></li>
     *
     *   <li><p> If a scheme-specific part is given then it is appended.  Any
     *   character that is not a <a href="#legal-chars">legal URI character</a>
     *   is <a href="#quote">quoted</a>.  </p></li>
     *
     *   <li><p> Finally, if a fragment is given then a hash character
     *   ({@code '#'}) is appended to the string, followed by the fragment.
     *   Any character that is not a legal URI character is quoted.  </p></li>
     *
     * </ol>
     *
     * <p> The resulting URI string is then parsed in order to create the new
     * URI instance as if by invoking the {@link #URI(String)} constructor;
     * this may cause a {@link URISyntaxException} to be thrown.  </p>
     *
     * @param   scheme    Scheme name
     * @param   ssp       Scheme-specific part
     * @param   fragment  Fragment
     *
     * @throws  URISyntaxException
     *          If the URI string constructed from the given components
     *          violates RFC&nbsp;2396
     */
    public URI(String scheme, String ssp, String fragment)
        throws URISyntaxException
    {
        new Parser(toString(scheme, ssp,
                            null, null, null, -1,
                            null, null, fragment))
            .parse(false);
    }

    
Constructs a simple URI consisting of only a scheme and a pre-validated
path. Provides a fast-path for some internal cases.
/**
     * Constructs a simple URI consisting of only a scheme and a pre-validated
     * path. Provides a fast-path for some internal cases.
     */
    URI(String scheme, String path) {
        assert validSchemeAndPath(scheme, path);
        this.scheme = scheme;
        this.path = path;
    }

    private static boolean validSchemeAndPath(String scheme, String path) {
        try {
            URI u = new URI(scheme + ":" + path);
            return scheme.equals(u.scheme) && path.equals(u.path);
        } catch (URISyntaxException e) {
            return false;
        }
    }

    
Creates a URI by parsing the given string.
 This convenience factory method works as if by invoking the URI(String) constructor; any URISyntaxException thrown by the constructor is caught and wrapped in a new IllegalArgumentException object, which is then thrown. 
 This method is provided for use in situations where it is known that the given string is a legal URI, for example for URI constants declared within in a program, and so it would be considered a programming error for the string not to parse as such. The constructors, which throw URISyntaxException directly, should be used situations where a URI is being constructed from user input or from some other source that may be prone to errors. 
Params:
str –   The string to be parsed into a URI
Throws:
NullPointerException –  If str is null
IllegalArgumentException – 
         If the given string violates RFC 2396
Returns:
The new URI/**
     * Creates a URI by parsing the given string.
     *
     * <p> This convenience factory method works as if by invoking the {@link
     * #URI(String)} constructor; any {@link URISyntaxException} thrown by the
     * constructor is caught and wrapped in a new {@link
     * IllegalArgumentException} object, which is then thrown.
     *
     * <p> This method is provided for use in situations where it is known that
     * the given string is a legal URI, for example for URI constants declared
     * within in a program, and so it would be considered a programming error
     * for the string not to parse as such.  The constructors, which throw
     * {@link URISyntaxException} directly, should be used situations where a
     * URI is being constructed from user input or from some other source that
     * may be prone to errors.  </p>
     *
     * @param  str   The string to be parsed into a URI
     * @return The new URI
     *
     * @throws  NullPointerException
     *          If {@code str} is {@code null}
     *
     * @throws  IllegalArgumentException
     *          If the given string violates RFC&nbsp;2396
     */
    public static URI create(String str) {
        try {
            return new URI(str);
        } catch (URISyntaxException x) {
            throw new IllegalArgumentException(x.getMessage(), x);
        }
    }


    // -- Operations --

    
Attempts to parse this URI's authority component, if defined, into
user-information, host, and port components.
 If this URI's authority component has already been recognized as
being server-based then it will already have been parsed into
user-information, host, and port components.  In this case, or if this
URI has no authority component, this method simply returns this URI.
 Otherwise this method attempts once more to parse the authority
component into user-information, host, and port components, and throws
an exception describing why the authority component could not be parsed
in that way.
 This method is provided because the generic URI syntax specified in
RFC 2396 cannot always distinguish a malformed server-based authority from a legitimate registry-based authority. It must therefore treat some instances of the former as instances of the latter. The authority component in the URI string "//foo:bar", for example, is not a legal server-based authority but it is legal as a registry-based authority. 
 In many common situations, for example when working URIs that are
known to be either URNs or URLs, the hierarchical URIs being used will
always be server-based.  They therefore must either be parsed as such or
treated as an error.  In these cases a statement such as
 URI u = new URI(str).parseServerAuthority(); 
 can be used to ensure that u always refers to a URI that, if
it has an authority component, has a server-based authority with proper
user-information, host, and port components.  Invoking this method also
ensures that if the authority could not be parsed in that way then an
appropriate diagnostic message can be issued based upon the exception
that is thrown. 
Throws:
URISyntaxException – 
         If the authority component of this URI is defined
         but cannot be parsed as a server-based authority
         according to RFC 2396
Returns:
 A URI whose authority field has been parsed
         as a server-based authority/**
     * Attempts to parse this URI's authority component, if defined, into
     * user-information, host, and port components.
     *
     * <p> If this URI's authority component has already been recognized as
     * being server-based then it will already have been parsed into
     * user-information, host, and port components.  In this case, or if this
     * URI has no authority component, this method simply returns this URI.
     *
     * <p> Otherwise this method attempts once more to parse the authority
     * component into user-information, host, and port components, and throws
     * an exception describing why the authority component could not be parsed
     * in that way.
     *
     * <p> This method is provided because the generic URI syntax specified in
     * <a href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>
     * cannot always distinguish a malformed server-based authority from a
     * legitimate registry-based authority.  It must therefore treat some
     * instances of the former as instances of the latter.  The authority
     * component in the URI string {@code "//foo:bar"}, for example, is not a
     * legal server-based authority but it is legal as a registry-based
     * authority.
     *
     * <p> In many common situations, for example when working URIs that are
     * known to be either URNs or URLs, the hierarchical URIs being used will
     * always be server-based.  They therefore must either be parsed as such or
     * treated as an error.  In these cases a statement such as
     *
     * <blockquote>
     * {@code URI }<i>u</i>{@code  = new URI(str).parseServerAuthority();}
     * </blockquote>
     *
     * <p> can be used to ensure that <i>u</i> always refers to a URI that, if
     * it has an authority component, has a server-based authority with proper
     * user-information, host, and port components.  Invoking this method also
     * ensures that if the authority could not be parsed in that way then an
     * appropriate diagnostic message can be issued based upon the exception
     * that is thrown. </p>
     *
     * @return  A URI whose authority field has been parsed
     *          as a server-based authority
     *
     * @throws  URISyntaxException
     *          If the authority component of this URI is defined
     *          but cannot be parsed as a server-based authority
     *          according to RFC&nbsp;2396
     */
    public URI parseServerAuthority()
        throws URISyntaxException
    {
        // We could be clever and cache the error message and index from the
        // exception thrown during the original parse, but that would require
        // either more fields or a more-obscure representation.
        if ((host != null) || (authority == null))
            return this;
        new Parser(toString()).parse(true);
        return this;
    }

    
Normalizes this URI's path.
 If this URI is opaque, or if its path is already in normal form,
then this URI is returned.  Otherwise a new URI is constructed that is
identical to this URI except that its path is computed by normalizing
this URI's path in a manner consistent with RFC 2396,
section 5.2, step 6, sub-steps c through f; that is:


  
 All "." segments are removed. 
  
 If a ".." segment is preceded by a non-".." segment then both of these segments are removed. This step is repeated until it is no longer applicable. 
  
 If the path is relative, and if its first segment contains a colon character (':'), then a "." segment is prepended. This prevents a relative URI with a path such as "a:b/c/d" from later being re-parsed as an opaque URI with a scheme of "a" and a scheme-specific part of "b/c/d". (Deviation from RFC 2396) 

 A normalized path will begin with one or more ".." segments if there were insufficient non-".." segments preceding them to allow their removal. A normalized path will begin with a "." segment if one was inserted by step 3 above. Otherwise, a normalized path will not contain any "." or ".." segments. 
Returns:
 A URI equivalent to this URI,
         but whose path is in normal form/**
     * Normalizes this URI's path.
     *
     * <p> If this URI is opaque, or if its path is already in normal form,
     * then this URI is returned.  Otherwise a new URI is constructed that is
     * identical to this URI except that its path is computed by normalizing
     * this URI's path in a manner consistent with <a
     * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,
     * section&nbsp;5.2, step&nbsp;6, sub-steps&nbsp;c through&nbsp;f; that is:
     * </p>
     *
     * <ol>
     *
     *   <li><p> All {@code "."} segments are removed. </p></li>
     *
     *   <li><p> If a {@code ".."} segment is preceded by a non-{@code ".."}
     *   segment then both of these segments are removed.  This step is
     *   repeated until it is no longer applicable. </p></li>
     *
     *   <li><p> If the path is relative, and if its first segment contains a
     *   colon character ({@code ':'}), then a {@code "."} segment is
     *   prepended.  This prevents a relative URI with a path such as
     *   {@code "a:b/c/d"} from later being re-parsed as an opaque URI with a
     *   scheme of {@code "a"} and a scheme-specific part of {@code "b/c/d"}.
     *   <b><i>(Deviation from RFC&nbsp;2396)</i></b> </p></li>
     *
     * </ol>
     *
     * <p> A normalized path will begin with one or more {@code ".."} segments
     * if there were insufficient non-{@code ".."} segments preceding them to
     * allow their removal.  A normalized path will begin with a {@code "."}
     * segment if one was inserted by step 3 above.  Otherwise, a normalized
     * path will not contain any {@code "."} or {@code ".."} segments. </p>
     *
     * @return  A URI equivalent to this URI,
     *          but whose path is in normal form
     */
    public URI normalize() {
        return normalize(this);
    }

    
Resolves the given URI against this URI.
 If the given URI is already absolute, or if this URI is opaque, then
the given URI is returned.
 If the given URI's fragment component is defined, its path component is empty, and its scheme, authority, and query components are undefined, then a URI with the given fragment but with all other components equal to those of this URI is returned. This allows a URI representing a standalone fragment reference, such as "#foo", to be usefully resolved against a base URI. 
 Otherwise this method constructs a new hierarchical URI in a manner
consistent with RFC 2396,
section 5.2; that is: 

  
 A new URI is constructed with this URI's scheme and the given
  URI's query and fragment components. 
  
 If the given URI has an authority component then the new URI's
  authority and path are taken from the given URI. 
  
 Otherwise the new URI's authority component is copied from
  this URI, and its path is computed as follows: 
  

    
 If the given URI's path is absolute then the new URI's path
    is taken from the given URI. 
    
 Otherwise the given URI's path is relative, and so the new URI's path is computed by resolving the path of the given URI against the path of this URI. This is done by concatenating all but the last segment of this URI's path, if any, with the given URI's path and then normalizing the result as if by invoking the normalize method. 
  

 The result of this method is absolute if, and only if, either this
URI is absolute or the given URI is absolute.  
Params:
uri –  The URI to be resolved against this URI
Throws:
NullPointerException –  If uri is null
Returns:
The resulting URI/**
     * Resolves the given URI against this URI.
     *
     * <p> If the given URI is already absolute, or if this URI is opaque, then
     * the given URI is returned.
     *
     * <p><a id="resolve-frag"></a> If the given URI's fragment component is
     * defined, its path component is empty, and its scheme, authority, and
     * query components are undefined, then a URI with the given fragment but
     * with all other components equal to those of this URI is returned.  This
     * allows a URI representing a standalone fragment reference, such as
     * {@code "#foo"}, to be usefully resolved against a base URI.
     *
     * <p> Otherwise this method constructs a new hierarchical URI in a manner
     * consistent with <a
     * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,
     * section&nbsp;5.2; that is: </p>
     *
     * <ol>
     *
     *   <li><p> A new URI is constructed with this URI's scheme and the given
     *   URI's query and fragment components. </p></li>
     *
     *   <li><p> If the given URI has an authority component then the new URI's
     *   authority and path are taken from the given URI. </p></li>
     *
     *   <li><p> Otherwise the new URI's authority component is copied from
     *   this URI, and its path is computed as follows: </p>
     *
     *   <ol>
     *
     *     <li><p> If the given URI's path is absolute then the new URI's path
     *     is taken from the given URI. </p></li>
     *
     *     <li><p> Otherwise the given URI's path is relative, and so the new
     *     URI's path is computed by resolving the path of the given URI
     *     against the path of this URI.  This is done by concatenating all but
     *     the last segment of this URI's path, if any, with the given URI's
     *     path and then normalizing the result as if by invoking the {@link
     *     #normalize() normalize} method. </p></li>
     *
     *   </ol></li>
     *
     * </ol>
     *
     * <p> The result of this method is absolute if, and only if, either this
     * URI is absolute or the given URI is absolute.  </p>
     *
     * @param  uri  The URI to be resolved against this URI
     * @return The resulting URI
     *
     * @throws  NullPointerException
     *          If {@code uri} is {@code null}
     */
    public URI resolve(URI uri) {
        return resolve(this, uri);
    }

    
Constructs a new URI by parsing the given string and then resolving it
against this URI.
 This convenience method works as if invoking it were equivalent to evaluating the expression 
resolve(URI.create(str)). 
Params:
str –   The string to be parsed into a URI
Throws:
NullPointerException –  If str is null
IllegalArgumentException – 
         If the given string violates RFC 2396
Returns:
The resulting URI/**
     * Constructs a new URI by parsing the given string and then resolving it
     * against this URI.
     *
     * <p> This convenience method works as if invoking it were equivalent to
     * evaluating the expression {@link #resolve(java.net.URI)
     * resolve}{@code (URI.}{@link #create(String) create}{@code (str))}. </p>
     *
     * @param  str   The string to be parsed into a URI
     * @return The resulting URI
     *
     * @throws  NullPointerException
     *          If {@code str} is {@code null}
     *
     * @throws  IllegalArgumentException
     *          If the given string violates RFC&nbsp;2396
     */
    public URI resolve(String str) {
        return resolve(URI.create(str));
    }

    
Relativizes the given URI against this URI.
 The relativization of the given URI against this URI is computed as
follows: 

  
 If either this URI or the given URI are opaque, or if the
  scheme and authority components of the two URIs are not identical, or
  if the path of this URI is not a prefix of the path of the given URI,
  then the given URI is returned. 
  
 Otherwise a new relative hierarchical URI is constructed with
  query and fragment components taken from the given URI and with a path
  component computed by removing this URI's path from the beginning of
  the given URI's path. 

Params:
uri –  The URI to be relativized against this URI
Throws:
NullPointerException –  If uri is null
Returns:
The resulting URI/**
     * Relativizes the given URI against this URI.
     *
     * <p> The relativization of the given URI against this URI is computed as
     * follows: </p>
     *
     * <ol>
     *
     *   <li><p> If either this URI or the given URI are opaque, or if the
     *   scheme and authority components of the two URIs are not identical, or
     *   if the path of this URI is not a prefix of the path of the given URI,
     *   then the given URI is returned. </p></li>
     *
     *   <li><p> Otherwise a new relative hierarchical URI is constructed with
     *   query and fragment components taken from the given URI and with a path
     *   component computed by removing this URI's path from the beginning of
     *   the given URI's path. </p></li>
     *
     * </ol>
     *
     * @param  uri  The URI to be relativized against this URI
     * @return The resulting URI
     *
     * @throws  NullPointerException
     *          If {@code uri} is {@code null}
     */
    public URI relativize(URI uri) {
        return relativize(this, uri);
    }

    
Constructs a URL from this URI.
 This convenience method works as if invoking it were equivalent to evaluating the expression new URL(this.toString()) after first checking that this URI is absolute. 
Throws:
IllegalArgumentException – 
         If this URL is not absolute
MalformedURLException – 
         If a protocol handler for the URL could not be found,
         or if some other error occurred while constructing the URL
Returns:
 A URL constructed from this URI/**
     * Constructs a URL from this URI.
     *
     * <p> This convenience method works as if invoking it were equivalent to
     * evaluating the expression {@code new URL(this.toString())} after
     * first checking that this URI is absolute. </p>
     *
     * @return  A URL constructed from this URI
     *
     * @throws  IllegalArgumentException
     *          If this URL is not absolute
     *
     * @throws  MalformedURLException
     *          If a protocol handler for the URL could not be found,
     *          or if some other error occurred while constructing the URL
     */
    public URL toURL() throws MalformedURLException {
        return URL.fromURI(this);
    }

    // -- Component access methods --

    
Returns the scheme component of this URI.
 The scheme component of a URI, if defined, only contains characters
in the alphanum category and in the string "-.+". A scheme always starts with an alpha character. 

The scheme component of a URI cannot contain escaped octets, hence this
method does not perform any decoding.
Returns:
 The scheme component of this URI, or null if the scheme is undefined/**
     * Returns the scheme component of this URI.
     *
     * <p> The scheme component of a URI, if defined, only contains characters
     * in the <i>alphanum</i> category and in the string {@code "-.+"}.  A
     * scheme always starts with an <i>alpha</i> character. <p>
     *
     * The scheme component of a URI cannot contain escaped octets, hence this
     * method does not perform any decoding.
     *
     * @return  The scheme component of this URI,
     *          or {@code null} if the scheme is undefined
     */
    public String getScheme() {
        return scheme;
    }

    
Tells whether or not this URI is absolute.
 A URI is absolute if, and only if, it has a scheme component. 
Returns:
 true if, and only if, this URI is absolute/**
     * Tells whether or not this URI is absolute.
     *
     * <p> A URI is absolute if, and only if, it has a scheme component. </p>
     *
     * @return  {@code true} if, and only if, this URI is absolute
     */
    public boolean isAbsolute() {
        return scheme != null;
    }

    
Tells whether or not this URI is opaque.
 A URI is opaque if, and only if, it is absolute and its
scheme-specific part does not begin with a slash character ('/').
An opaque URI has a scheme, a scheme-specific part, and possibly
a fragment; all other components are undefined. 
Returns:
 true if, and only if, this URI is opaque/**
     * Tells whether or not this URI is opaque.
     *
     * <p> A URI is opaque if, and only if, it is absolute and its
     * scheme-specific part does not begin with a slash character ('/').
     * An opaque URI has a scheme, a scheme-specific part, and possibly
     * a fragment; all other components are undefined. </p>
     *
     * @return  {@code true} if, and only if, this URI is opaque
     */
    public boolean isOpaque() {
        return path == null;
    }

    
Returns the raw scheme-specific part of this URI.  The scheme-specific
part is never undefined, though it may be empty.
 The scheme-specific part of a URI only contains legal URI
characters. 
Returns:
 The raw scheme-specific part of this URI (never null)/**
     * Returns the raw scheme-specific part of this URI.  The scheme-specific
     * part is never undefined, though it may be empty.
     *
     * <p> The scheme-specific part of a URI only contains legal URI
     * characters. </p>
     *
     * @return  The raw scheme-specific part of this URI
     *          (never {@code null})
     */
    public String getRawSchemeSpecificPart() {
        String part = schemeSpecificPart;
        if (part != null) {
            return part;
        }

        String s = string;
        if (s != null) {
            // if string is defined, components will have been parsed
            int start = 0;
            int end = s.length();
            if (scheme != null) {
                start = scheme.length() + 1;
            }
            if (fragment != null) {
                end -= fragment.length() + 1;
            }
            if (path != null && path.length() == end - start) {
                part = path;
            } else {
                part = s.substring(start, end);
            }
        } else {
            StringBuilder sb = new StringBuilder();
            appendSchemeSpecificPart(sb, null, getAuthority(), getUserInfo(),
                                 host, port, getPath(), getQuery());
            part = sb.toString();
        }
        return schemeSpecificPart = part;
    }

    
Returns the decoded scheme-specific part of this URI.
 The string returned by this method is equal to that returned by the getRawSchemeSpecificPart method except that all sequences of escaped octets are decoded.  
Returns:
 The decoded scheme-specific part of this URI (never null)/**
     * Returns the decoded scheme-specific part of this URI.
     *
     * <p> The string returned by this method is equal to that returned by the
     * {@link #getRawSchemeSpecificPart() getRawSchemeSpecificPart} method
     * except that all sequences of escaped octets are <a
     * href="#decode">decoded</a>.  </p>
     *
     * @return  The decoded scheme-specific part of this URI
     *          (never {@code null})
     */
    public String getSchemeSpecificPart() {
        String part = decodedSchemeSpecificPart;
        if (part == null) {
            decodedSchemeSpecificPart = part = decode(getRawSchemeSpecificPart());
        }
        return part;
    }

    
Returns the raw authority component of this URI.
 The authority component of a URI, if defined, only contains the commercial-at character ('@') and characters in the unreserved, punct, escaped, and other
categories.  If the authority is server-based then it is further
constrained to have valid user-information, host, and port
components. 
Returns:
 The raw authority component of this URI, or null if the authority is undefined/**
     * Returns the raw authority component of this URI.
     *
     * <p> The authority component of a URI, if defined, only contains the
     * commercial-at character ({@code '@'}) and characters in the
     * <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, and <i>other</i>
     * categories.  If the authority is server-based then it is further
     * constrained to have valid user-information, host, and port
     * components. </p>
     *
     * @return  The raw authority component of this URI,
     *          or {@code null} if the authority is undefined
     */
    public String getRawAuthority() {
        return authority;
    }

    
Returns the decoded authority component of this URI.
 The string returned by this method is equal to that returned by the getRawAuthority method except that all sequences of escaped octets are decoded.  
Returns:
 The decoded authority component of this URI, or null if the authority is undefined/**
     * Returns the decoded authority component of this URI.
     *
     * <p> The string returned by this method is equal to that returned by the
     * {@link #getRawAuthority() getRawAuthority} method except that all
     * sequences of escaped octets are <a href="#decode">decoded</a>.  </p>
     *
     * @return  The decoded authority component of this URI,
     *          or {@code null} if the authority is undefined
     */
    public String getAuthority() {
        String auth = decodedAuthority;
        if ((auth == null) && (authority != null)) {
            decodedAuthority = auth = decode(authority);
        }
        return auth;
    }

    
Returns the raw user-information component of this URI.
 The user-information component of a URI, if defined, only contains
characters in the unreserved, punct, escaped, and
other categories. 
Returns:
 The raw user-information component of this URI, or null if the user information is undefined/**
     * Returns the raw user-information component of this URI.
     *
     * <p> The user-information component of a URI, if defined, only contains
     * characters in the <i>unreserved</i>, <i>punct</i>, <i>escaped</i>, and
     * <i>other</i> categories. </p>
     *
     * @return  The raw user-information component of this URI,
     *          or {@code null} if the user information is undefined
     */
    public String getRawUserInfo() {
        return userInfo;
    }

    
Returns the decoded user-information component of this URI.
 The string returned by this method is equal to that returned by the getRawUserInfo method except that all sequences of escaped octets are decoded.  
Returns:
 The decoded user-information component of this URI, or null if the user information is undefined/**
     * Returns the decoded user-information component of this URI.
     *
     * <p> The string returned by this method is equal to that returned by the
     * {@link #getRawUserInfo() getRawUserInfo} method except that all
     * sequences of escaped octets are <a href="#decode">decoded</a>.  </p>
     *
     * @return  The decoded user-information component of this URI,
     *          or {@code null} if the user information is undefined
     */
    public String getUserInfo() {
        String user = decodedUserInfo;
        if ((user == null) && (userInfo != null)) {
            decodedUserInfo = user = decode(userInfo);
        }
        return user;
    }

    
Returns the host component of this URI.
 The host component of a URI, if defined, will have one of the
following forms: 

  
 A domain name consisting of one or more labels separated by period characters ('.'), optionally followed by a period character. Each label consists of alphanum characters as well as hyphen characters ('-'), though hyphens never occur as the first or last characters in a label. The rightmost label of a domain name consisting of two or more labels, begins with an alpha character. 
  
 A dotted-quad IPv4 address of the form
  digit+.digit+.digit+.digit+, where no digit sequence is longer than three characters and no
  sequence has a value larger than 255. 
  
 An IPv6 address enclosed in square brackets ('[' and ']') and consisting of hexadecimal digits, colon characters (':'), and possibly an embedded IPv4 address. The full syntax of IPv6 addresses is specified in RFC 2373: IPv6
  Addressing Architecture.  

The host component of a URI cannot contain escaped octets, hence this
method does not perform any decoding.
Returns:
 The host component of this URI, or null if the host is undefined/**
     * Returns the host component of this URI.
     *
     * <p> The host component of a URI, if defined, will have one of the
     * following forms: </p>
     *
     * <ul>
     *
     *   <li><p> A domain name consisting of one or more <i>labels</i>
     *   separated by period characters ({@code '.'}), optionally followed by
     *   a period character.  Each label consists of <i>alphanum</i> characters
     *   as well as hyphen characters ({@code '-'}), though hyphens never
     *   occur as the first or last characters in a label. The rightmost
     *   label of a domain name consisting of two or more labels, begins
     *   with an <i>alpha</i> character. </li>
     *
     *   <li><p> A dotted-quad IPv4 address of the form
     *   <i>digit</i>{@code +.}<i>digit</i>{@code +.}<i>digit</i>{@code +.}<i>digit</i>{@code +},
     *   where no <i>digit</i> sequence is longer than three characters and no
     *   sequence has a value larger than 255. </p></li>
     *
     *   <li><p> An IPv6 address enclosed in square brackets ({@code '['} and
     *   {@code ']'}) and consisting of hexadecimal digits, colon characters
     *   ({@code ':'}), and possibly an embedded IPv4 address.  The full
     *   syntax of IPv6 addresses is specified in <a
     *   href="http://www.ietf.org/rfc/rfc2373.txt"><i>RFC&nbsp;2373: IPv6
     *   Addressing Architecture</i></a>.  </p></li>
     *
     * </ul>
     *
     * The host component of a URI cannot contain escaped octets, hence this
     * method does not perform any decoding.
     *
     * @return  The host component of this URI,
     *          or {@code null} if the host is undefined
     */
    public String getHost() {
        return host;
    }

    
Returns the port number of this URI.
 The port component of a URI, if defined, is a non-negative
integer. 
Returns:
 The port component of this URI, or -1 if the port is undefined/**
     * Returns the port number of this URI.
     *
     * <p> The port component of a URI, if defined, is a non-negative
     * integer. </p>
     *
     * @return  The port component of this URI,
     *          or {@code -1} if the port is undefined
     */
    public int getPort() {
        return port;
    }

    
Returns the raw path component of this URI.
 The path component of a URI, if defined, only contains the slash character ('/'), the commercial-at character ('@'), and characters in the unreserved, punct, escaped,
and other categories. 
Returns:
 The path component of this URI, or null if the path is undefined/**
     * Returns the raw path component of this URI.
     *
     * <p> The path component of a URI, if defined, only contains the slash
     * character ({@code '/'}), the commercial-at character ({@code '@'}),
     * and characters in the <i>unreserved</i>, <i>punct</i>, <i>escaped</i>,
     * and <i>other</i> categories. </p>
     *
     * @return  The path component of this URI,
     *          or {@code null} if the path is undefined
     */
    public String getRawPath() {
        return path;
    }

    
Returns the decoded path component of this URI.
 The string returned by this method is equal to that returned by the getRawPath method except that all sequences of escaped octets are decoded.  
Returns:
 The decoded path component of this URI, or null if the path is undefined/**
     * Returns the decoded path component of this URI.
     *
     * <p> The string returned by this method is equal to that returned by the
     * {@link #getRawPath() getRawPath} method except that all sequences of
     * escaped octets are <a href="#decode">decoded</a>.  </p>
     *
     * @return  The decoded path component of this URI,
     *          or {@code null} if the path is undefined
     */
    public String getPath() {
        String decoded = decodedPath;
        if ((decoded == null) && (path != null)) {
            decodedPath = decoded = decode(path);
        }
        return decoded;
    }

    
Returns the raw query component of this URI.
 The query component of a URI, if defined, only contains legal URI
characters. 
Returns:
 The raw query component of this URI, or null if the query is undefined/**
     * Returns the raw query component of this URI.
     *
     * <p> The query component of a URI, if defined, only contains legal URI
     * characters. </p>
     *
     * @return  The raw query component of this URI,
     *          or {@code null} if the query is undefined
     */
    public String getRawQuery() {
        return query;
    }

    
Returns the decoded query component of this URI.
 The string returned by this method is equal to that returned by the getRawQuery method except that all sequences of escaped octets are decoded.  
Returns:
 The decoded query component of this URI, or null if the query is undefined/**
     * Returns the decoded query component of this URI.
     *
     * <p> The string returned by this method is equal to that returned by the
     * {@link #getRawQuery() getRawQuery} method except that all sequences of
     * escaped octets are <a href="#decode">decoded</a>.  </p>
     *
     * @return  The decoded query component of this URI,
     *          or {@code null} if the query is undefined
     */
    public String getQuery() {
        String decoded = decodedQuery;
        if ((decoded == null) && (query != null)) {
            decodedQuery = decoded = decode(query, false);
        }
        return decoded;
    }

    
Returns the raw fragment component of this URI.
 The fragment component of a URI, if defined, only contains legal URI
characters. 
Returns:
 The raw fragment component of this URI, or null if the fragment is undefined/**
     * Returns the raw fragment component of this URI.
     *
     * <p> The fragment component of a URI, if defined, only contains legal URI
     * characters. </p>
     *
     * @return  The raw fragment component of this URI,
     *          or {@code null} if the fragment is undefined
     */
    public String getRawFragment() {
        return fragment;
    }

    
Returns the decoded fragment component of this URI.
 The string returned by this method is equal to that returned by the getRawFragment method except that all sequences of escaped octets are decoded.  
Returns:
 The decoded fragment component of this URI, or null if the fragment is undefined/**
     * Returns the decoded fragment component of this URI.
     *
     * <p> The string returned by this method is equal to that returned by the
     * {@link #getRawFragment() getRawFragment} method except that all
     * sequences of escaped octets are <a href="#decode">decoded</a>.  </p>
     *
     * @return  The decoded fragment component of this URI,
     *          or {@code null} if the fragment is undefined
     */
    public String getFragment() {
        String decoded = decodedFragment;
        if ((decoded == null) && (fragment != null)) {
            decodedFragment = decoded = decode(fragment, false);
        }
        return decoded;
    }


    // -- Equality, comparison, hash code, toString, and serialization --

    
Tests this URI for equality with another object.
 If the given object is not a URI then this method immediately returns false. 
 For two URIs to be considered equal requires that either both are
opaque or both are hierarchical.  Their schemes must either both be
undefined or else be equal without regard to case. Their fragments
must either both be undefined or else be equal.
 For two opaque URIs to be considered equal, their scheme-specific
parts must be equal.
 For two hierarchical URIs to be considered equal, their paths must
be equal and their queries must either both be undefined or else be
equal.  Their authorities must either both be undefined, or both be
registry-based, or both be server-based.  If their authorities are
defined and are registry-based, then they must be equal.  If their
authorities are defined and are server-based, then their hosts must be
equal without regard to case, their port numbers must be equal, and
their user-information components must be equal.
 When testing the user-information, path, query, fragment, authority,
or scheme-specific parts of two URIs for equality, the raw forms rather
than the encoded forms of these components are compared and the
hexadecimal digits of escaped octets are compared without regard to
case.
 This method satisfies the general contract of the Object.equals method. 
Params:
ob –   The object to which this object is to be compared
Returns:
 true if, and only if, the given object is a URI that is identical to this URI/**
     * Tests this URI for equality with another object.
     *
     * <p> If the given object is not a URI then this method immediately
     * returns {@code false}.
     *
     * <p> For two URIs to be considered equal requires that either both are
     * opaque or both are hierarchical.  Their schemes must either both be
     * undefined or else be equal without regard to case. Their fragments
     * must either both be undefined or else be equal.
     *
     * <p> For two opaque URIs to be considered equal, their scheme-specific
     * parts must be equal.
     *
     * <p> For two hierarchical URIs to be considered equal, their paths must
     * be equal and their queries must either both be undefined or else be
     * equal.  Their authorities must either both be undefined, or both be
     * registry-based, or both be server-based.  If their authorities are
     * defined and are registry-based, then they must be equal.  If their
     * authorities are defined and are server-based, then their hosts must be
     * equal without regard to case, their port numbers must be equal, and
     * their user-information components must be equal.
     *
     * <p> When testing the user-information, path, query, fragment, authority,
     * or scheme-specific parts of two URIs for equality, the raw forms rather
     * than the encoded forms of these components are compared and the
     * hexadecimal digits of escaped octets are compared without regard to
     * case.
     *
     * <p> This method satisfies the general contract of the {@link
     * java.lang.Object#equals(Object) Object.equals} method. </p>
     *
     * @param   ob   The object to which this object is to be compared
     *
     * @return  {@code true} if, and only if, the given object is a URI that
     *          is identical to this URI
     */
    public boolean equals(Object ob) {
        if (ob == this)
            return true;
        if (!(ob instanceof URI))
            return false;
        URI that = (URI)ob;
        if (this.isOpaque() != that.isOpaque()) return false;
        if (!equalIgnoringCase(this.scheme, that.scheme)) return false;
        if (!equal(this.fragment, that.fragment)) return false;

        // Opaque
        if (this.isOpaque())
            return equal(this.schemeSpecificPart, that.schemeSpecificPart);

        // Hierarchical
        if (!equal(this.path, that.path)) return false;
        if (!equal(this.query, that.query)) return false;

        // Authorities
        if (this.authority == that.authority) return true;
        if (this.host != null) {
            // Server-based
            if (!equal(this.userInfo, that.userInfo)) return false;
            if (!equalIgnoringCase(this.host, that.host)) return false;
            if (this.port != that.port) return false;
        } else if (this.authority != null) {
            // Registry-based
            if (!equal(this.authority, that.authority)) return false;
        } else if (this.authority != that.authority) {
            return false;
        }

        return true;
    }

    
Returns a hash-code value for this URI. The hash code is based upon all of the URI's components, and satisfies the general contract of the Object.hashCode method. 
Returns:
 A hash-code value for this URI/**
     * Returns a hash-code value for this URI.  The hash code is based upon all
     * of the URI's components, and satisfies the general contract of the
     * {@link java.lang.Object#hashCode() Object.hashCode} method.
     *
     * @return  A hash-code value for this URI
     */
    public int hashCode() {
        int h = hash;
        if (h == 0) {
            h = hashIgnoringCase(0, scheme);
            h = hash(h, fragment);
            if (isOpaque()) {
                h = hash(h, schemeSpecificPart);
            } else {
                h = hash(h, path);
                h = hash(h, query);
                if (host != null) {
                    h = hash(h, userInfo);
                    h = hashIgnoringCase(h, host);
                    h += 1949 * port;
                } else {
                    h = hash(h, authority);
                }
            }
            if (h != 0) {
                hash = h;
            }
        }
        return h;
    }

    
Compares this URI to another object, which must be a URI.
 When comparing corresponding components of two URIs, if one component is undefined but the other is defined then the first is considered to be less than the second. Unless otherwise noted, string components are ordered according to their natural, case-sensitive ordering as defined by the 
String.compareTo method. String components that are subject to encoding are compared by comparing their raw forms rather than their encoded forms. 
 The ordering of URIs is defined as follows: 

  
 Two URIs with different schemes are ordered according the
  ordering of their schemes, without regard to case. 
  
 A hierarchical URI is considered to be less than an opaque URI
  with an identical scheme. 
  
 Two opaque URIs with identical schemes are ordered according
  to the ordering of their scheme-specific parts. 
  
 Two opaque URIs with identical schemes and scheme-specific
  parts are ordered according to the ordering of their
  fragments. 
  
 Two hierarchical URIs with identical schemes are ordered
  according to the ordering of their authority components: 
  

    
 If both authority components are server-based then the URIs
    are ordered according to their user-information components; if these
    components are identical then the URIs are ordered according to the
    ordering of their hosts, without regard to case; if the hosts are
    identical then the URIs are ordered according to the ordering of
    their ports. 
    
 If one or both authority components are registry-based then
    the URIs are ordered according to the ordering of their authority
    components. 
  
  
 Finally, two hierarchical URIs with identical schemes and
  authority components are ordered according to the ordering of their
  paths; if their paths are identical then they are ordered according to
  the ordering of their queries; if the queries are identical then they
  are ordered according to the order of their fragments. 

 This method satisfies the general contract of the Comparable.compareTo method. 
Params:
that – 
         The object to which this URI is to be compared
Throws:
ClassCastException – 
         If the given object is not a URI
Returns:
 A negative integer, zero, or a positive integer as this URI is
         less than, equal to, or greater than the given URI/**
     * Compares this URI to another object, which must be a URI.
     *
     * <p> When comparing corresponding components of two URIs, if one
     * component is undefined but the other is defined then the first is
     * considered to be less than the second.  Unless otherwise noted, string
     * components are ordered according to their natural, case-sensitive
     * ordering as defined by the {@link java.lang.String#compareTo(Object)
     * String.compareTo} method.  String components that are subject to
     * encoding are compared by comparing their raw forms rather than their
     * encoded forms.
     *
     * <p> The ordering of URIs is defined as follows: </p>
     *
     * <ul>
     *
     *   <li><p> Two URIs with different schemes are ordered according the
     *   ordering of their schemes, without regard to case. </p></li>
     *
     *   <li><p> A hierarchical URI is considered to be less than an opaque URI
     *   with an identical scheme. </p></li>
     *
     *   <li><p> Two opaque URIs with identical schemes are ordered according
     *   to the ordering of their scheme-specific parts. </p></li>
     *
     *   <li><p> Two opaque URIs with identical schemes and scheme-specific
     *   parts are ordered according to the ordering of their
     *   fragments. </p></li>
     *
     *   <li><p> Two hierarchical URIs with identical schemes are ordered
     *   according to the ordering of their authority components: </p>
     *
     *   <ul>
     *
     *     <li><p> If both authority components are server-based then the URIs
     *     are ordered according to their user-information components; if these
     *     components are identical then the URIs are ordered according to the
     *     ordering of their hosts, without regard to case; if the hosts are
     *     identical then the URIs are ordered according to the ordering of
     *     their ports. </p></li>
     *
     *     <li><p> If one or both authority components are registry-based then
     *     the URIs are ordered according to the ordering of their authority
     *     components. </p></li>
     *
     *   </ul></li>
     *
     *   <li><p> Finally, two hierarchical URIs with identical schemes and
     *   authority components are ordered according to the ordering of their
     *   paths; if their paths are identical then they are ordered according to
     *   the ordering of their queries; if the queries are identical then they
     *   are ordered according to the order of their fragments. </p></li>
     *
     * </ul>
     *
     * <p> This method satisfies the general contract of the {@link
     * java.lang.Comparable#compareTo(Object) Comparable.compareTo}
     * method. </p>
     *
     * @param   that
     *          The object to which this URI is to be compared
     *
     * @return  A negative integer, zero, or a positive integer as this URI is
     *          less than, equal to, or greater than the given URI
     *
     * @throws  ClassCastException
     *          If the given object is not a URI
     */
    public int compareTo(URI that) {
        int c;

        if ((c = compareIgnoringCase(this.scheme, that.scheme)) != 0)
            return c;

        if (this.isOpaque()) {
            if (that.isOpaque()) {
                // Both opaque
                if ((c = compare(this.schemeSpecificPart,
                                 that.schemeSpecificPart)) != 0)
                    return c;
                return compare(this.fragment, that.fragment);
            }
            return +1;                  // Opaque > hierarchical
        } else if (that.isOpaque()) {
            return -1;                  // Hierarchical < opaque
        }

        // Hierarchical
        if ((this.host != null) && (that.host != null)) {
            // Both server-based
            if ((c = compare(this.userInfo, that.userInfo)) != 0)
                return c;
            if ((c = compareIgnoringCase(this.host, that.host)) != 0)
                return c;
            if ((c = this.port - that.port) != 0)
                return c;
        } else {
            // If one or both authorities are registry-based then we simply
            // compare them in the usual, case-sensitive way.  If one is
            // registry-based and one is server-based then the strings are
            // guaranteed to be unequal, hence the comparison will never return
            // zero and the compareTo and equals methods will remain
            // consistent.
            if ((c = compare(this.authority, that.authority)) != 0) return c;
        }

        if ((c = compare(this.path, that.path)) != 0) return c;
        if ((c = compare(this.query, that.query)) != 0) return c;
        return compare(this.fragment, that.fragment);
    }

    
Returns the content of this URI as a string.
 If this URI was created by invoking one of the constructors in this
class then a string equivalent to the original input string, or to the
string computed from the originally-given components, as appropriate, is
returned.  Otherwise this URI was created by normalization, resolution,
or relativization, and so a string is constructed from this URI's
components according to the rules specified in RFC 2396,
section 5.2, step 7. 
Returns:
 The string form of this URI/**
     * Returns the content of this URI as a string.
     *
     * <p> If this URI was created by invoking one of the constructors in this
     * class then a string equivalent to the original input string, or to the
     * string computed from the originally-given components, as appropriate, is
     * returned.  Otherwise this URI was created by normalization, resolution,
     * or relativization, and so a string is constructed from this URI's
     * components according to the rules specified in <a
     * href="http://www.ietf.org/rfc/rfc2396.txt">RFC&nbsp;2396</a>,
     * section&nbsp;5.2, step&nbsp;7. </p>
     *
     * @return  The string form of this URI
     */
    public String toString() {
        String s = string;
        if (s == null) {
            s = defineString();
        }
        return s;
    }

    private String defineString() {
        String s = string;
        if (s != null) {
            return s;
        }

        StringBuilder sb = new StringBuilder();
        if (scheme != null) {
            sb.append(scheme);
            sb.append(':');
        }
        if (isOpaque()) {
            sb.append(schemeSpecificPart);
        } else {
            if (host != null) {
                sb.append("//");
                if (userInfo != null) {
                    sb.append(userInfo);
                    sb.append('@');
                }
                boolean needBrackets = ((host.indexOf(':') >= 0)
                        && !host.startsWith("[")
                        && !host.endsWith("]"));
                if (needBrackets) sb.append('[');
                sb.append(host);
                if (needBrackets) sb.append(']');
                if (port != -1) {
                    sb.append(':');
                    sb.append(port);
                }
            } else if (authority != null) {
                sb.append("//");
                sb.append(authority);
            }
            if (path != null)
                sb.append(path);
            if (query != null) {
                sb.append('?');
                sb.append(query);
            }
        }
        if (fragment != null) {
            sb.append('#');
            sb.append(fragment);
        }
        return string = sb.toString();
    }

    
Returns the content of this URI as a US-ASCII string.
 If this URI does not contain any characters in the other category then an invocation of this method will return the same value as an invocation of the toString method. Otherwise this method works as if by invoking that method and then encoding the result.  
Returns:
 The string form of this URI, encoded as needed
         so that it only contains characters in the US-ASCII
         charset/**
     * Returns the content of this URI as a US-ASCII string.
     *
     * <p> If this URI does not contain any characters in the <i>other</i>
     * category then an invocation of this method will return the same value as
     * an invocation of the {@link #toString() toString} method.  Otherwise
     * this method works as if by invoking that method and then <a
     * href="#encode">encoding</a> the result.  </p>
     *
     * @return  The string form of this URI, encoded as needed
     *          so that it only contains characters in the US-ASCII
     *          charset
     */
    public String toASCIIString() {
        return encode(toString());
    }


    // -- Serialization support --

    
Saves the content of this URI to the given serial stream.
 The only serializable field of a URI instance is its string field. That field is given a value, if it does not have one already, and then the ObjectOutputStream.defaultWriteObject() method of the given object-output stream is invoked. 
Params:
os –  The object-output stream to which this object
            is to be written/**
     * Saves the content of this URI to the given serial stream.
     *
     * <p> The only serializable field of a URI instance is its {@code string}
     * field.  That field is given a value, if it does not have one already,
     * and then the {@link java.io.ObjectOutputStream#defaultWriteObject()}
     * method of the given object-output stream is invoked. </p>
     *
     * @param  os  The object-output stream to which this object
     *             is to be written
     */
    private void writeObject(ObjectOutputStream os)
        throws IOException
    {
        defineString();
        os.defaultWriteObject();        // Writes the string field only
    }

    
Reconstitutes a URI from the given serial stream.
 The ObjectInputStream.defaultReadObject() method is invoked to read the value of the string field. The result is then parsed in the usual way. 
Params:
is –  The object-input stream from which this object
            is being read/**
     * Reconstitutes a URI from the given serial stream.
     *
     * <p> The {@link java.io.ObjectInputStream#defaultReadObject()} method is
     * invoked to read the value of the {@code string} field.  The result is
     * then parsed in the usual way.
     *
     * @param  is  The object-input stream from which this object
     *             is being read
     */
    private void readObject(ObjectInputStream is)
        throws ClassNotFoundException, IOException
    {
        port = -1;                      // Argh
        is.defaultReadObject();
        try {
            new Parser(string).parse(false);
        } catch (URISyntaxException x) {
            IOException y = new InvalidObjectException("Invalid URI");
            y.initCause(x);
            throw y;
        }
    }


    // -- End of public methods --


    // -- Utility methods for string-field comparison and hashing --

    // These methods return appropriate values for null string arguments,
    // thereby simplifying the equals, hashCode, and compareTo methods.
    //
    // The case-ignoring methods should only be applied to strings whose
    // characters are all known to be US-ASCII.  Because of this restriction,
    // these methods are faster than the similar methods in the String class.

    // US-ASCII only
    private static int toLower(char c) {
        if ((c >= 'A') && (c <= 'Z'))
            return c + ('a' - 'A');
        return c;
    }

    // US-ASCII only
    private static int toUpper(char c) {
        if ((c >= 'a') && (c <= 'z'))
            return c - ('a' - 'A');
        return c;
    }

    private static boolean equal(String s, String t) {
        if (s == t) return true;
        if ((s != null) && (t != null)) {
            if (s.length() != t.length())
                return false;
            if (s.indexOf('%') < 0)
                return s.equals(t);
            int n = s.length();
            for (int i = 0; i < n;) {
                char c = s.charAt(i);
                char d = t.charAt(i);
                if (c != '%') {
                    if (c != d)
                        return false;
                    i++;
                    continue;
                }
                if (d != '%')
                    return false;
                i++;
                if (toLower(s.charAt(i)) != toLower(t.charAt(i)))
                    return false;
                i++;
                if (toLower(s.charAt(i)) != toLower(t.charAt(i)))
                    return false;
                i++;
            }
            return true;
        }
        return false;
    }

    // US-ASCII only
    private static boolean equalIgnoringCase(String s, String t) {
        if (s == t) return true;
        if ((s != null) && (t != null)) {
            int n = s.length();
            if (t.length() != n)
                return false;
            for (int i = 0; i < n; i++) {
                if (toLower(s.charAt(i)) != toLower(t.charAt(i)))
                    return false;
            }
            return true;
        }
        return false;
    }

    private static int hash(int hash, String s) {
        if (s == null) return hash;
        return s.indexOf('%') < 0 ? hash * 127 + s.hashCode()
                                  : normalizedHash(hash, s);
    }


    private static int normalizedHash(int hash, String s) {
        int h = 0;
        for (int index = 0; index < s.length(); index++) {
            char ch = s.charAt(index);
            h = 31 * h + ch;
            if (ch == '%') {
                /*
                 * Process the next two encoded characters
                 */
                for (int i = index + 1; i < index + 3; i++)
                    h = 31 * h + toUpper(s.charAt(i));
                index += 2;
            }
        }
        return hash * 127 + h;
    }

    // US-ASCII only
    private static int hashIgnoringCase(int hash, String s) {
        if (s == null) return hash;
        int h = hash;
        int n = s.length();
        for (int i = 0; i < n; i++)
            h = 31 * h + toLower(s.charAt(i));
        return h;
    }

    private static int compare(String s, String t) {
        if (s == t) return 0;
        if (s != null) {
            if (t != null)
                return s.compareTo(t);
            else
                return +1;
        } else {
            return -1;
        }
    }

    // US-ASCII only
    private static int compareIgnoringCase(String s, String t) {
        if (s == t) return 0;
        if (s != null) {
            if (t != null) {
                int sn = s.length();
                int tn = t.length();
                int n = sn < tn ? sn : tn;
                for (int i = 0; i < n; i++) {
                    int c = toLower(s.charAt(i)) - toLower(t.charAt(i));
                    if (c != 0)
                        return c;
                }
                return sn - tn;
            }
            return +1;
        } else {
            return -1;
        }
    }


    // -- String construction --

    // If a scheme is given then the path, if given, must be absolute
    //
    private static void checkPath(String s, String scheme, String path)
        throws URISyntaxException
    {
        if (scheme != null) {
            if ((path != null)
                && ((path.length() > 0) && (path.charAt(0) != '/')))
                throw new URISyntaxException(s,
                                             "Relative path in absolute URI");
        }
    }

    private void appendAuthority(StringBuilder sb,
                                 String authority,
                                 String userInfo,
                                 String host,
                                 int port)
    {
        if (host != null) {
            sb.append("//");
            if (userInfo != null) {
                sb.append(quote(userInfo, L_USERINFO, H_USERINFO));
                sb.append('@');
            }
            boolean needBrackets = ((host.indexOf(':') >= 0)
                                    && !host.startsWith("[")
                                    && !host.endsWith("]"));
            if (needBrackets) sb.append('[');
            sb.append(host);
            if (needBrackets) sb.append(']');
            if (port != -1) {
                sb.append(':');
                sb.append(port);
            }
        } else if (authority != null) {
            sb.append("//");
            if (authority.startsWith("[")) {
                // authority should (but may not) contain an embedded IPv6 address
                int end = authority.indexOf(']');
                String doquote = authority, dontquote = "";
                if (end != -1 && authority.indexOf(':') != -1) {
                    // the authority contains an IPv6 address
                    if (end == authority.length()) {
                        dontquote = authority;
                        doquote = "";
                    } else {
                        dontquote = authority.substring(0 , end + 1);
                        doquote = authority.substring(end + 1);
                    }
                }
                sb.append(dontquote);
                sb.append(quote(doquote,
                            L_REG_NAME | L_SERVER,
                            H_REG_NAME | H_SERVER));
            } else {
                sb.append(quote(authority,
                            L_REG_NAME | L_SERVER,
                            H_REG_NAME | H_SERVER));
            }
        }
    }

    private void appendSchemeSpecificPart(StringBuilder sb,
                                          String opaquePart,
                                          String authority,
                                          String userInfo,
                                          String host,
                                          int port,
                                          String path,
                                          String query)
    {
        if (opaquePart != null) {
            /* check if SSP begins with an IPv6 address
             * because we must not quote a literal IPv6 address
             */
            if (opaquePart.startsWith("//[")) {
                int end =  opaquePart.indexOf(']');
                if (end != -1 && opaquePart.indexOf(':')!=-1) {
                    String doquote, dontquote;
                    if (end == opaquePart.length()) {
                        dontquote = opaquePart;
                        doquote = "";
                    } else {
                        dontquote = opaquePart.substring(0,end+1);
                        doquote = opaquePart.substring(end+1);
                    }
                    sb.append (dontquote);
                    sb.append(quote(doquote, L_URIC, H_URIC));
                }
            } else {
                sb.append(quote(opaquePart, L_URIC, H_URIC));
            }
        } else {
            appendAuthority(sb, authority, userInfo, host, port);
            if (path != null)
                sb.append(quote(path, L_PATH, H_PATH));
            if (query != null) {
                sb.append('?');
                sb.append(quote(query, L_URIC, H_URIC));
            }
        }
    }

    private void appendFragment(StringBuilder sb, String fragment) {
        if (fragment != null) {
            sb.append('#');
            sb.append(quote(fragment, L_URIC, H_URIC));
        }
    }

    private String toString(String scheme,
                            String opaquePart,
                            String authority,
                            String userInfo,
                            String host,
                            int port,
                            String path,
                            String query,
                            String fragment)
    {
        StringBuilder sb = new StringBuilder();
        if (scheme != null) {
            sb.append(scheme);
            sb.append(':');
        }
        appendSchemeSpecificPart(sb, opaquePart,
                                 authority, userInfo, host, port,
                                 path, query);
        appendFragment(sb, fragment);
        return sb.toString();
    }

    // -- Normalization, resolution, and relativization --

    // RFC2396 5.2 (6)
    private static String resolvePath(String base, String child,
                                      boolean absolute)
    {
        int i = base.lastIndexOf('/');
        int cn = child.length();
        String path = "";

        if (cn == 0) {
            // 5.2 (6a)
            if (i >= 0)
                path = base.substring(0, i + 1);
        } else {
            StringBuilder sb = new StringBuilder(base.length() + cn);
            // 5.2 (6a)
            if (i >= 0)
                sb.append(base, 0, i + 1);
            // 5.2 (6b)
            sb.append(child);
            path = sb.toString();
        }

        // 5.2 (6c-f)
        String np = normalize(path);

        // 5.2 (6g): If the result is absolute but the path begins with "../",
        // then we simply leave the path as-is

        return np;
    }

    // RFC2396 5.2
    private static URI resolve(URI base, URI child) {
        // check if child if opaque first so that NPE is thrown
        // if child is null.
        if (child.isOpaque() || base.isOpaque())
            return child;

        // 5.2 (2): Reference to current document (lone fragment)
        if ((child.scheme == null) && (child.authority == null)
            && child.path.isEmpty() && (child.fragment != null)
            && (child.query == null)) {
            if ((base.fragment != null)
                && child.fragment.equals(base.fragment)) {
                return base;
            }
            URI ru = new URI();
            ru.scheme = base.scheme;
            ru.authority = base.authority;
            ru.userInfo = base.userInfo;
            ru.host = base.host;
            ru.port = base.port;
            ru.path = base.path;
            ru.fragment = child.fragment;
            ru.query = base.query;
            return ru;
        }

        // 5.2 (3): Child is absolute
        if (child.scheme != null)
            return child;

        URI ru = new URI();             // Resolved URI
        ru.scheme = base.scheme;
        ru.query = child.query;
        ru.fragment = child.fragment;

        // 5.2 (4): Authority
        if (child.authority == null) {
            ru.authority = base.authority;
            ru.host = base.host;
            ru.userInfo = base.userInfo;
            ru.port = base.port;

            String cp = (child.path == null) ? "" : child.path;
            if ((cp.length() > 0) && (cp.charAt(0) == '/')) {
                // 5.2 (5): Child path is absolute
                ru.path = child.path;
            } else {
                // 5.2 (6): Resolve relative path
                ru.path = resolvePath(base.path, cp, base.isAbsolute());
            }
        } else {
            ru.authority = child.authority;
            ru.host = child.host;
            ru.userInfo = child.userInfo;
            ru.host = child.host;
            ru.port = child.port;
            ru.path = child.path;
        }

        // 5.2 (7): Recombine (nothing to do here)
        return ru;
    }

    // If the given URI's path is normal then return the URI;
    // o.w., return a new URI containing the normalized path.
    //
    private static URI normalize(URI u) {
        if (u.isOpaque() || (u.path == null) || (u.path.length() == 0))
            return u;

        String np = normalize(u.path);
        if (np == u.path)
            return u;

        URI v = new URI();
        v.scheme = u.scheme;
        v.fragment = u.fragment;
        v.authority = u.authority;
        v.userInfo = u.userInfo;
        v.host = u.host;
        v.port = u.port;
        v.path = np;
        v.query = u.query;
        return v;
    }

    // If both URIs are hierarchical, their scheme and authority components are
    // identical, and the base path is a prefix of the child's path, then
    // return a relative URI that, when resolved against the base, yields the
    // child; otherwise, return the child.
    //
    private static URI relativize(URI base, URI child) {
        // check if child if opaque first so that NPE is thrown
        // if child is null.
        if (child.isOpaque() || base.isOpaque())
            return child;
        if (!equalIgnoringCase(base.scheme, child.scheme)
            || !equal(base.authority, child.authority))
            return child;

        String bp = normalize(base.path);
        String cp = normalize(child.path);
        if (!bp.equals(cp)) {
            if (!bp.endsWith("/"))
                bp = bp + "/";
            if (!cp.startsWith(bp))
                return child;
        }

        URI v = new URI();
        v.path = cp.substring(bp.length());
        v.query = child.query;
        v.fragment = child.fragment;
        return v;
    }



    // -- Path normalization --

    // The following algorithm for path normalization avoids the creation of a
    // string object for each segment, as well as the use of a string buffer to
    // compute the final result, by using a single char array and editing it in
    // place.  The array is first split into segments, replacing each slash
    // with '\0' and creating a segment-index array, each element of which is
    // the index of the first char in the corresponding segment.  We then walk
    // through both arrays, removing ".", "..", and other segments as necessary
    // by setting their entries in the index array to -1.  Finally, the two
    // arrays are used to rejoin the segments and compute the final result.
    //
    // This code is based upon src/solaris/native/java/io/canonicalize_md.c


    // Check the given path to see if it might need normalization.  A path
    // might need normalization if it contains duplicate slashes, a "."
    // segment, or a ".." segment.  Return -1 if no further normalization is
    // possible, otherwise return the number of segments found.
    //
    // This method takes a string argument rather than a char array so that
    // this test can be performed without invoking path.toCharArray().
    //
    private static int needsNormalization(String path) {
        boolean normal = true;
        int ns = 0;                     // Number of segments
        int end = path.length() - 1;    // Index of last char in path
        int p = 0;                      // Index of next char in path

        // Skip initial slashes
        while (p <= end) {
            if (path.charAt(p) != '/') break;
            p++;
        }
        if (p > 1) normal = false;

        // Scan segments
        while (p <= end) {

            // Looking at "." or ".." ?
            if ((path.charAt(p) == '.')
                && ((p == end)
                    || ((path.charAt(p + 1) == '/')
                        || ((path.charAt(p + 1) == '.')
                            && ((p + 1 == end)
                                || (path.charAt(p + 2) == '/')))))) {
                normal = false;
            }
            ns++;

            // Find beginning of next segment
            while (p <= end) {
                if (path.charAt(p++) != '/')
                    continue;

                // Skip redundant slashes
                while (p <= end) {
                    if (path.charAt(p) != '/') break;
                    normal = false;
                    p++;
                }

                break;
            }
        }

        return normal ? -1 : ns;
    }


    // Split the given path into segments, replacing slashes with nulls and
    // filling in the given segment-index array.
    //
    // Preconditions:
    //   segs.length == Number of segments in path
    //
    // Postconditions:
    //   All slashes in path replaced by '\0'
    //   segs[i] == Index of first char in segment i (0 <= i < segs.length)
    //
    private static void split(char[] path, int[] segs) {
        int end = path.length - 1;      // Index of last char in path
        int p = 0;                      // Index of next char in path
        int i = 0;                      // Index of current segment

        // Skip initial slashes
        while (p <= end) {
            if (path[p] != '/') break;
            path[p] = '\0';
            p++;
        }

        while (p <= end) {

            // Note start of segment
            segs[i++] = p++;

            // Find beginning of next segment
            while (p <= end) {
                if (path[p++] != '/')
                    continue;
                path[p - 1] = '\0';

                // Skip redundant slashes
                while (p <= end) {
                    if (path[p] != '/') break;
                    path[p++] = '\0';
                }
                break;
            }
        }

        if (i != segs.length)
            throw new InternalError();  // ASSERT
    }


    // Join the segments in the given path according to the given segment-index
    // array, ignoring those segments whose index entries have been set to -1,
    // and inserting slashes as needed.  Return the length of the resulting
    // path.
    //
    // Preconditions:
    //   segs[i] == -1 implies segment i is to be ignored
    //   path computed by split, as above, with '\0' having replaced '/'
    //
    // Postconditions:
    //   path[0] .. path[return value] == Resulting path
    //
    private static int join(char[] path, int[] segs) {
        int ns = segs.length;           // Number of segments
        int end = path.length - 1;      // Index of last char in path
        int p = 0;                      // Index of next path char to write

        if (path[p] == '\0') {
            // Restore initial slash for absolute paths
            path[p++] = '/';
        }

        for (int i = 0; i < ns; i++) {
            int q = segs[i];            // Current segment
            if (q == -1)
                // Ignore this segment
                continue;

            if (p == q) {
                // We're already at this segment, so just skip to its end
                while ((p <= end) && (path[p] != '\0'))
                    p++;
                if (p <= end) {
                    // Preserve trailing slash
                    path[p++] = '/';
                }
            } else if (p < q) {
                // Copy q down to p
                while ((q <= end) && (path[q] != '\0'))
                    path[p++] = path[q++];
                if (q <= end) {
                    // Preserve trailing slash
                    path[p++] = '/';
                }
            } else
                throw new InternalError(); // ASSERT false
        }

        return p;
    }


    // Remove "." segments from the given path, and remove segment pairs
    // consisting of a non-".." segment followed by a ".." segment.
    //
    private static void removeDots(char[] path, int[] segs) {
        int ns = segs.length;
        int end = path.length - 1;

        for (int i = 0; i < ns; i++) {
            int dots = 0;               // Number of dots found (0, 1, or 2)

            // Find next occurrence of "." or ".."
            do {
                int p = segs[i];
                if (path[p] == '.') {
                    if (p == end) {
                        dots = 1;
                        break;
                    } else if (path[p + 1] == '\0') {
                        dots = 1;
                        break;
                    } else if ((path[p + 1] == '.')
                               && ((p + 1 == end)
                                   || (path[p + 2] == '\0'))) {
                        dots = 2;
                        break;
                    }
                }
                i++;
            } while (i < ns);
            if ((i > ns) || (dots == 0))
                break;

            if (dots == 1) {
                // Remove this occurrence of "."
                segs[i] = -1;
            } else {
                // If there is a preceding non-".." segment, remove both that
                // segment and this occurrence of ".."; otherwise, leave this
                // ".." segment as-is.
                int j;
                for (j = i - 1; j >= 0; j--) {
                    if (segs[j] != -1) break;
                }
                if (j >= 0) {
                    int q = segs[j];
                    if (!((path[q] == '.')
                          && (path[q + 1] == '.')
                          && (path[q + 2] == '\0'))) {
                        segs[i] = -1;
                        segs[j] = -1;
                    }
                }
            }
        }
    }


    // DEVIATION: If the normalized path is relative, and if the first
    // segment could be parsed as a scheme name, then prepend a "." segment
    //
    private static void maybeAddLeadingDot(char[] path, int[] segs) {

        if (path[0] == '\0')
            // The path is absolute
            return;

        int ns = segs.length;
        int f = 0;                      // Index of first segment
        while (f < ns) {
            if (segs[f] >= 0)
                break;
            f++;
        }
        if ((f >= ns) || (f == 0))
            // The path is empty, or else the original first segment survived,
            // in which case we already know that no leading "." is needed
            return;

        int p = segs[f];
        while ((p < path.length) && (path[p] != ':') && (path[p] != '\0')) p++;
        if (p >= path.length || path[p] == '\0')
            // No colon in first segment, so no "." needed
            return;

        // At this point we know that the first segment is unused,
        // hence we can insert a "." segment at that position
        path[0] = '.';
        path[1] = '\0';
        segs[0] = 0;
    }


    // Normalize the given path string.  A normal path string has no empty
    // segments (i.e., occurrences of "//"), no segments equal to ".", and no
    // segments equal to ".." that are preceded by a segment not equal to "..".
    // In contrast to Unix-style pathname normalization, for URI paths we
    // always retain trailing slashes.
    //
    private static String normalize(String ps) {

        // Does this path need normalization?
        int ns = needsNormalization(ps);        // Number of segments
        if (ns < 0)
            // Nope -- just return it
            return ps;

        char[] path = ps.toCharArray();         // Path in char-array form

        // Split path into segments
        int[] segs = new int[ns];               // Segment-index array
        split(path, segs);

        // Remove dots
        removeDots(path, segs);

        // Prevent scheme-name confusion
        maybeAddLeadingDot(path, segs);

        // Join the remaining segments and return the result
        String s = new String(path, 0, join(path, segs));
        if (s.equals(ps)) {
            // string was already normalized
            return ps;
        }
        return s;
    }



    // -- Character classes for parsing --

    // RFC2396 precisely specifies which characters in the US-ASCII charset are
    // permissible in the various components of a URI reference.  We here
    // define a set of mask pairs to aid in enforcing these restrictions.  Each
    // mask pair consists of two longs, a low mask and a high mask.  Taken
    // together they represent a 128-bit mask, where bit i is set iff the
    // character with value i is permitted.
    //
    // This approach is more efficient than sequentially searching arrays of
    // permitted characters.  It could be made still more efficient by
    // precompiling the mask information so that a character's presence in a
    // given mask could be determined by a single table lookup.

    // To save startup time, we manually calculate the low-/highMask constants.
    // For reference, the following methods were used to calculate the values:

    // Compute the low-order mask for the characters in the given string
    //     private static long lowMask(String chars) {
    //        int n = chars.length();
    //        long m = 0;
    //        for (int i = 0; i < n; i++) {
    //            char c = chars.charAt(i);
    //            if (c < 64)
    //                m |= (1L << c);
    //        }
    //        return m;
    //    }

    // Compute the high-order mask for the characters in the given string
    //    private static long highMask(String chars) {
    //        int n = chars.length();
    //        long m = 0;
    //        for (int i = 0; i < n; i++) {
    //            char c = chars.charAt(i);
    //            if ((c >= 64) && (c < 128))
    //                m |= (1L << (c - 64));
    //        }
    //        return m;
    //    }

    // Compute a low-order mask for the characters
    // between first and last, inclusive
    //    private static long lowMask(char first, char last) {
    //        long m = 0;
    //        int f = Math.max(Math.min(first, 63), 0);
    //        int l = Math.max(Math.min(last, 63), 0);
    //        for (int i = f; i <= l; i++)
    //            m |= 1L << i;
    //        return m;
    //    }

    // Compute a high-order mask for the characters
    // between first and last, inclusive
    //    private static long highMask(char first, char last) {
    //        long m = 0;
    //        int f = Math.max(Math.min(first, 127), 64) - 64;
    //        int l = Math.max(Math.min(last, 127), 64) - 64;
    //        for (int i = f; i <= l; i++)
    //            m |= 1L << i;
    //        return m;
    //    }

    // Tell whether the given character is permitted by the given mask pair
    private static boolean match(char c, long lowMask, long highMask) {
        if (c == 0) // 0 doesn't have a slot in the mask. So, it never matches.
            return false;
        if (c < 64)
            return ((1L << c) & lowMask) != 0;
        if (c < 128)
            return ((1L << (c - 64)) & highMask) != 0;
        return false;
    }

    // Character-class masks, in reverse order from RFC2396 because
    // initializers for static fields cannot make forward references.

    // digit    = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |
    //            "8" | "9"
    private static final long L_DIGIT = 0x3FF000000000000L; // lowMask('0', '9');
    private static final long H_DIGIT = 0L;

    // upalpha  = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" |
    //            "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" |
    //            "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z"
    private static final long L_UPALPHA = 0L;
    private static final long H_UPALPHA = 0x7FFFFFEL; // highMask('A', 'Z');

    // lowalpha = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" |
    //            "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" |
    //            "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z"
    private static final long L_LOWALPHA = 0L;
    private static final long H_LOWALPHA = 0x7FFFFFE00000000L; // highMask('a', 'z');

    // alpha         = lowalpha | upalpha
    private static final long L_ALPHA = L_LOWALPHA | L_UPALPHA;
    private static final long H_ALPHA = H_LOWALPHA | H_UPALPHA;

    // alphanum      = alpha | digit
    private static final long L_ALPHANUM = L_DIGIT | L_ALPHA;
    private static final long H_ALPHANUM = H_DIGIT | H_ALPHA;

    // hex           = digit | "A" | "B" | "C" | "D" | "E" | "F" |
    //                         "a" | "b" | "c" | "d" | "e" | "f"
    private static final long L_HEX = L_DIGIT;
    private static final long H_HEX = 0x7E0000007EL; // highMask('A', 'F') | highMask('a', 'f');

    // mark          = "-" | "_" | "." | "!" | "~" | "*" | "'" |
    //                 "(" | ")"
    private static final long L_MARK = 0x678200000000L; // lowMask("-_.!~*'()");
    private static final long H_MARK = 0x4000000080000000L; // highMask("-_.!~*'()");

    // unreserved    = alphanum | mark
    private static final long L_UNRESERVED = L_ALPHANUM | L_MARK;
    private static final long H_UNRESERVED = H_ALPHANUM | H_MARK;

    // reserved      = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+" |
    //                 "$" | "," | "[" | "]"
    // Added per RFC2732: "[", "]"
    private static final long L_RESERVED = 0xAC00985000000000L; // lowMask(";/?:@&=+$,[]");
    private static final long H_RESERVED = 0x28000001L; // highMask(";/?:@&=+$,[]");

    // The zero'th bit is used to indicate that escape pairs and non-US-ASCII
    // characters are allowed; this is handled by the scanEscape method below.
    private static final long L_ESCAPED = 1L;
    private static final long H_ESCAPED = 0L;

    // uric          = reserved | unreserved | escaped
    private static final long L_URIC = L_RESERVED | L_UNRESERVED | L_ESCAPED;
    private static final long H_URIC = H_RESERVED | H_UNRESERVED | H_ESCAPED;

    // pchar         = unreserved | escaped |
    //                 ":" | "@" | "&" | "=" | "+" | "$" | ","
    private static final long L_PCHAR
        = L_UNRESERVED | L_ESCAPED | 0x2400185000000000L; // lowMask(":@&=+$,");
    private static final long H_PCHAR
        = H_UNRESERVED | H_ESCAPED | 0x1L; // highMask(":@&=+$,");

    // All valid path characters
    private static final long L_PATH = L_PCHAR | 0x800800000000000L; // lowMask(";/");
    private static final long H_PATH = H_PCHAR; // highMask(";/") == 0x0L;

    // Dash, for use in domainlabel and toplabel
    private static final long L_DASH = 0x200000000000L; // lowMask("-");
    private static final long H_DASH = 0x0L; // highMask("-");

    // Dot, for use in hostnames
    private static final long L_DOT = 0x400000000000L; // lowMask(".");
    private static final long H_DOT = 0x0L; // highMask(".");

    // userinfo      = *( unreserved | escaped |
    //                    ";" | ":" | "&" | "=" | "+" | "$" | "," )
    private static final long L_USERINFO
        = L_UNRESERVED | L_ESCAPED | 0x2C00185000000000L; // lowMask(";:&=+$,");
    private static final long H_USERINFO
        = H_UNRESERVED | H_ESCAPED; // | highMask(";:&=+$,") == 0L;

    // reg_name      = 1*( unreserved | escaped | "$" | "," |
    //                     ";" | ":" | "@" | "&" | "=" | "+" )
    private static final long L_REG_NAME
        = L_UNRESERVED | L_ESCAPED | 0x2C00185000000000L; // lowMask("$,;:@&=+");
    private static final long H_REG_NAME
        = H_UNRESERVED | H_ESCAPED | 0x1L; // highMask("$,;:@&=+");

    // All valid characters for server-based authorities
    private static final long L_SERVER
        = L_USERINFO | L_ALPHANUM | L_DASH | 0x400400000000000L; // lowMask(".:@[]");
    private static final long H_SERVER
        = H_USERINFO | H_ALPHANUM | H_DASH | 0x28000001L; // highMask(".:@[]");

    // Special case of server authority that represents an IPv6 address
    // In this case, a % does not signify an escape sequence
    private static final long L_SERVER_PERCENT
        = L_SERVER | 0x2000000000L; // lowMask("%");
    private static final long H_SERVER_PERCENT
        = H_SERVER; // | highMask("%") == 0L;

    // scheme        = alpha *( alpha | digit | "+" | "-" | "." )
    private static final long L_SCHEME = L_ALPHA | L_DIGIT | 0x680000000000L; // lowMask("+-.");
    private static final long H_SCHEME = H_ALPHA | H_DIGIT; // | highMask("+-.") == 0L

    // scope_id = alpha | digit | "_" | "."
    private static final long L_SCOPE_ID
        = L_ALPHANUM | 0x400000000000L; // lowMask("_.");
    private static final long H_SCOPE_ID
        = H_ALPHANUM | 0x80000000L; // highMask("_.");

    // -- Escaping and encoding --

    private static final char[] hexDigits = {
        '0', '1', '2', '3', '4', '5', '6', '7',
        '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
    };

    private static void appendEscape(StringBuilder sb, byte b) {
        sb.append('%');
        sb.append(hexDigits[(b >> 4) & 0x0f]);
        sb.append(hexDigits[(b >> 0) & 0x0f]);
    }

    private static void appendEncoded(StringBuilder sb, char c) {
        ByteBuffer bb = null;
        try {
            bb = ThreadLocalCoders.encoderFor("UTF-8")
                .encode(CharBuffer.wrap("" + c));
        } catch (CharacterCodingException x) {
            assert false;
        }
        while (bb.hasRemaining()) {
            int b = bb.get() & 0xff;
            if (b >= 0x80)
                appendEscape(sb, (byte)b);
            else
                sb.append((char)b);
        }
    }

    // Quote any characters in s that are not permitted
    // by the given mask pair
    //
    private static String quote(String s, long lowMask, long highMask) {
        StringBuilder sb = null;
        boolean allowNonASCII = ((lowMask & L_ESCAPED) != 0);
        for (int i = 0; i < s.length(); i++) {
            char c = s.charAt(i);
            if (c < '\u0080') {
                if (!match(c, lowMask, highMask)) {
                    if (sb == null) {
                        sb = new StringBuilder();
                        sb.append(s, 0, i);
                    }
                    appendEscape(sb, (byte)c);
                } else {
                    if (sb != null)
                        sb.append(c);
                }
            } else if (allowNonASCII
                       && (Character.isSpaceChar(c)
                           || Character.isISOControl(c))) {
                if (sb == null) {
                    sb = new StringBuilder();
                    sb.append(s, 0, i);
                }
                appendEncoded(sb, c);
            } else {
                if (sb != null)
                    sb.append(c);
            }
        }
        return (sb == null) ? s : sb.toString();
    }

    // Encodes all characters >= \u0080 into escaped, normalized UTF-8 octets,
    // assuming that s is otherwise legal
    //
    private static String encode(String s) {
        int n = s.length();
        if (n == 0)
            return s;

        // First check whether we actually need to encode
        for (int i = 0;;) {
            if (s.charAt(i) >= '\u0080')
                break;
            if (++i >= n)
                return s;
        }

        String ns = Normalizer.normalize(s, Normalizer.Form.NFC);
        ByteBuffer bb = null;
        try {
            bb = ThreadLocalCoders.encoderFor("UTF-8")
                .encode(CharBuffer.wrap(ns));
        } catch (CharacterCodingException x) {
            assert false;
        }

        StringBuilder sb = new StringBuilder();
        while (bb.hasRemaining()) {
            int b = bb.get() & 0xff;
            if (b >= 0x80)
                appendEscape(sb, (byte)b);
            else
                sb.append((char)b);
        }
        return sb.toString();
    }

    private static int decode(char c) {
        if ((c >= '0') && (c <= '9'))
            return c - '0';
        if ((c >= 'a') && (c <= 'f'))
            return c - 'a' + 10;
        if ((c >= 'A') && (c <= 'F'))
            return c - 'A' + 10;
        assert false;
        return -1;
    }

    private static byte decode(char c1, char c2) {
        return (byte)(  ((decode(c1) & 0xf) << 4)
                      | ((decode(c2) & 0xf) << 0));
    }

    // Evaluates all escapes in s, applying UTF-8 decoding if needed.  Assumes
    // that escapes are well-formed syntactically, i.e., of the form %XX.  If a
    // sequence of escaped octets is not valid UTF-8 then the erroneous octets
    // are replaced with '\uFFFD'.
    // Exception: any "%" found between "[]" is left alone. It is an IPv6 literal
    //            with a scope_id
    //
    private static String decode(String s) {
        return decode(s, true);
    }

    // This method was introduced as a generalization of URI.decode method
    // to provide a fix for JDK-8037396
    private static String decode(String s, boolean ignorePercentInBrackets) {
        if (s == null)
            return s;
        int n = s.length();
        if (n == 0)
            return s;
        if (s.indexOf('%') < 0)
            return s;

        StringBuilder sb = new StringBuilder(n);
        ByteBuffer bb = ByteBuffer.allocate(n);
        CharBuffer cb = CharBuffer.allocate(n);
        CharsetDecoder dec = ThreadLocalCoders.decoderFor("UTF-8")
                .onMalformedInput(CodingErrorAction.REPLACE)
                .onUnmappableCharacter(CodingErrorAction.REPLACE);

        // This is not horribly efficient, but it will do for now
        char c = s.charAt(0);
        boolean betweenBrackets = false;

        for (int i = 0; i < n;) {
            assert c == s.charAt(i);    // Loop invariant
            if (c == '[') {
                betweenBrackets = true;
            } else if (betweenBrackets && c == ']') {
                betweenBrackets = false;
            }
            if (c != '%' || (betweenBrackets && ignorePercentInBrackets)) {
                sb.append(c);
                if (++i >= n)
                    break;
                c = s.charAt(i);
                continue;
            }
            bb.clear();
            int ui = i;
            for (;;) {
                assert (n - i >= 2);
                bb.put(decode(s.charAt(++i), s.charAt(++i)));
                if (++i >= n)
                    break;
                c = s.charAt(i);
                if (c != '%')
                    break;
            }
            bb.flip();
            cb.clear();
            dec.reset();
            CoderResult cr = dec.decode(bb, cb, true);
            assert cr.isUnderflow();
            cr = dec.flush(cb);
            assert cr.isUnderflow();
            sb.append(cb.flip().toString());
        }

        return sb.toString();
    }


    // -- Parsing --

    // For convenience we wrap the input URI string in a new instance of the
    // following internal class.  This saves always having to pass the input
    // string as an argument to each internal scan/parse method.

    private class Parser {

        private String input;           // URI input string
        private boolean requireServerAuthority = false;

        Parser(String s) {
            input = s;
            string = s;
        }

        // -- Methods for throwing URISyntaxException in various ways --

        private void fail(String reason) throws URISyntaxException {
            throw new URISyntaxException(input, reason);
        }

        private void fail(String reason, int p) throws URISyntaxException {
            throw new URISyntaxException(input, reason, p);
        }

        private void failExpecting(String expected, int p)
            throws URISyntaxException
        {
            fail("Expected " + expected, p);
        }


        // -- Simple access to the input string --

        // Tells whether start < end and, if so, whether charAt(start) == c
        //
        private boolean at(int start, int end, char c) {
            return (start < end) && (input.charAt(start) == c);
        }

        // Tells whether start + s.length() < end and, if so,
        // whether the chars at the start position match s exactly
        //
        private boolean at(int start, int end, String s) {
            int p = start;
            int sn = s.length();
            if (sn > end - p)
                return false;
            int i = 0;
            while (i < sn) {
                if (input.charAt(p++) != s.charAt(i)) {
                    break;
                }
                i++;
            }
            return (i == sn);
        }


        // -- Scanning --

        // The various scan and parse methods that follow use a uniform
        // convention of taking the current start position and end index as
        // their first two arguments.  The start is inclusive while the end is
        // exclusive, just as in the String class, i.e., a start/end pair
        // denotes the left-open interval [start, end) of the input string.
        //
        // These methods never proceed past the end position.  They may return
        // -1 to indicate outright failure, but more often they simply return
        // the position of the first char after the last char scanned.  Thus
        // a typical idiom is
        //
        //     int p = start;
        //     int q = scan(p, end, ...);
        //     if (q > p)
        //         // We scanned something
        //         ...;
        //     else if (q == p)
        //         // We scanned nothing
        //         ...;
        //     else if (q == -1)
        //         // Something went wrong
        //         ...;


        // Scan a specific char: If the char at the given start position is
        // equal to c, return the index of the next char; otherwise, return the
        // start position.
        //
        private int scan(int start, int end, char c) {
            if ((start < end) && (input.charAt(start) == c))
                return start + 1;
            return start;
        }

        // Scan forward from the given start position.  Stop at the first char
        // in the err string (in which case -1 is returned), or the first char
        // in the stop string (in which case the index of the preceding char is
        // returned), or the end of the input string (in which case the length
        // of the input string is returned).  May return the start position if
        // nothing matches.
        //
        private int scan(int start, int end, String err, String stop) {
            int p = start;
            while (p < end) {
                char c = input.charAt(p);
                if (err.indexOf(c) >= 0)
                    return -1;
                if (stop.indexOf(c) >= 0)
                    break;
                p++;
            }
            return p;
        }

        // Scan forward from the given start position.  Stop at the first char
        // in the stop string (in which case the index of the preceding char is
        // returned), or the end of the input string (in which case the length
        // of the input string is returned).  May return the start position if
        // nothing matches.
        //
        private int scan(int start, int end, String stop) {
            int p = start;
            while (p < end) {
                char c = input.charAt(p);
                if (stop.indexOf(c) >= 0)
                    break;
                p++;
            }
            return p;
        }

        // Scan a potential escape sequence, starting at the given position,
        // with the given first char (i.e., charAt(start) == c).
        //
        // This method assumes that if escapes are allowed then visible
        // non-US-ASCII chars are also allowed.
        //
        private int scanEscape(int start, int n, char first)
            throws URISyntaxException
        {
            int p = start;
            char c = first;
            if (c == '%') {
                // Process escape pair
                if ((p + 3 <= n)
                    && match(input.charAt(p + 1), L_HEX, H_HEX)
                    && match(input.charAt(p + 2), L_HEX, H_HEX)) {
                    return p + 3;
                }
                fail("Malformed escape pair", p);
            } else if ((c > 128)
                       && !Character.isSpaceChar(c)
                       && !Character.isISOControl(c)) {
                // Allow unescaped but visible non-US-ASCII chars
                return p + 1;
            }
            return p;
        }

        // Scan chars that match the given mask pair
        //
        private int scan(int start, int n, long lowMask, long highMask)
            throws URISyntaxException
        {
            int p = start;
            while (p < n) {
                char c = input.charAt(p);
                if (match(c, lowMask, highMask)) {
                    p++;
                    continue;
                }
                if ((lowMask & L_ESCAPED) != 0) {
                    int q = scanEscape(p, n, c);
                    if (q > p) {
                        p = q;
                        continue;
                    }
                }
                break;
            }
            return p;
        }

        // Check that each of the chars in [start, end) matches the given mask
        //
        private void checkChars(int start, int end,
                                long lowMask, long highMask,
                                String what)
            throws URISyntaxException
        {
            int p = scan(start, end, lowMask, highMask);
            if (p < end)
                fail("Illegal character in " + what, p);
        }

        // Check that the char at position p matches the given mask
        //
        private void checkChar(int p,
                               long lowMask, long highMask,
                               String what)
            throws URISyntaxException
        {
            checkChars(p, p + 1, lowMask, highMask, what);
        }


        // -- Parsing --

        // [<scheme>:]<scheme-specific-part>[#<fragment>]
        //
        void parse(boolean rsa) throws URISyntaxException {
            requireServerAuthority = rsa;
            int n = input.length();
            int p = scan(0, n, "/?#", ":");
            if ((p >= 0) && at(p, n, ':')) {
                if (p == 0)
                    failExpecting("scheme name", 0);
                checkChar(0, L_ALPHA, H_ALPHA, "scheme name");
                checkChars(1, p, L_SCHEME, H_SCHEME, "scheme name");
                scheme = input.substring(0, p);
                p++;                    // Skip ':'
                if (at(p, n, '/')) {
                    p = parseHierarchical(p, n);
                } else {
                    // opaque; need to create the schemeSpecificPart
                    int q = scan(p, n, "#");
                    if (q <= p)
                        failExpecting("scheme-specific part", p);
                    checkChars(p, q, L_URIC, H_URIC, "opaque part");
                    schemeSpecificPart = input.substring(p, q);
                    p = q;
                }
            } else {
                p = parseHierarchical(0, n);
            }
            if (at(p, n, '#')) {
                checkChars(p + 1, n, L_URIC, H_URIC, "fragment");
                fragment = input.substring(p + 1, n);
                p = n;
            }
            if (p < n)
                fail("end of URI", p);
        }

        // [//authority]<path>[?<query>]
        //
        // DEVIATION from RFC2396: We allow an empty authority component as
        // long as it's followed by a non-empty path, query component, or
        // fragment component.  This is so that URIs such as "file:///foo/bar"
        // will parse.  This seems to be the intent of RFC2396, though the
        // grammar does not permit it.  If the authority is empty then the
        // userInfo, host, and port components are undefined.
        //
        // DEVIATION from RFC2396: We allow empty relative paths.  This seems
        // to be the intent of RFC2396, but the grammar does not permit it.
        // The primary consequence of this deviation is that "#f" parses as a
        // relative URI with an empty path.
        //
        private int parseHierarchical(int start, int n)
            throws URISyntaxException
        {
            int p = start;
            if (at(p, n, '/') && at(p + 1, n, '/')) {
                p += 2;
                int q = scan(p, n, "/?#");
                if (q > p) {
                    p = parseAuthority(p, q);
                } else if (q < n) {
                    // DEVIATION: Allow empty authority prior to non-empty
                    // path, query component or fragment identifier
                } else
                    failExpecting("authority", p);
            }
            int q = scan(p, n, "?#"); // DEVIATION: May be empty
            checkChars(p, q, L_PATH, H_PATH, "path");
            path = input.substring(p, q);
            p = q;
            if (at(p, n, '?')) {
                p++;
                q = scan(p, n, "#");
                checkChars(p, q, L_URIC, H_URIC, "query");
                query = input.substring(p, q);
                p = q;
            }
            return p;
        }

        // authority     = server | reg_name
        //
        // Ambiguity: An authority that is a registry name rather than a server
        // might have a prefix that parses as a server.  We use the fact that
        // the authority component is always followed by '/' or the end of the
        // input string to resolve this: If the complete authority did not
        // parse as a server then we try to parse it as a registry name.
        //
        private int parseAuthority(int start, int n)
            throws URISyntaxException
        {
            int p = start;
            int q = p;
            URISyntaxException ex = null;

            boolean serverChars;
            boolean regChars;

            if (scan(p, n, "]") > p) {
                // contains a literal IPv6 address, therefore % is allowed
                serverChars = (scan(p, n, L_SERVER_PERCENT, H_SERVER_PERCENT) == n);
            } else {
                serverChars = (scan(p, n, L_SERVER, H_SERVER) == n);
            }
            regChars = (scan(p, n, L_REG_NAME, H_REG_NAME) == n);

            if (regChars && !serverChars) {
                // Must be a registry-based authority
                authority = input.substring(p, n);
                return n;
            }

            if (serverChars) {
                // Might be (probably is) a server-based authority, so attempt
                // to parse it as such.  If the attempt fails, try to treat it
                // as a registry-based authority.
                try {
                    q = parseServer(p, n);
                    if (q < n)
                        failExpecting("end of authority", q);
                    authority = input.substring(p, n);
                } catch (URISyntaxException x) {
                    // Undo results of failed parse
                    userInfo = null;
                    host = null;
                    port = -1;
                    if (requireServerAuthority) {
                        // If we're insisting upon a server-based authority,
                        // then just re-throw the exception
                        throw x;
                    } else {
                        // Save the exception in case it doesn't parse as a
                        // registry either
                        ex = x;
                        q = p;
                    }
                }
            }

            if (q < n) {
                if (regChars) {
                    // Registry-based authority
                    authority = input.substring(p, n);
                } else if (ex != null) {
                    // Re-throw exception; it was probably due to
                    // a malformed IPv6 address
                    throw ex;
                } else {
                    fail("Illegal character in authority", q);
                }
            }

            return n;
        }


        // [<userinfo>@]<host>[:<port>]
        //
        private int parseServer(int start, int n)
            throws URISyntaxException
        {
            int p = start;
            int q;

            // userinfo
            q = scan(p, n, "/?#", "@");
            if ((q >= p) && at(q, n, '@')) {
                checkChars(p, q, L_USERINFO, H_USERINFO, "user info");
                userInfo = input.substring(p, q);
                p = q + 1;              // Skip '@'
            }

            // hostname, IPv4 address, or IPv6 address
            if (at(p, n, '[')) {
                // DEVIATION from RFC2396: Support IPv6 addresses, per RFC2732
                p++;
                q = scan(p, n, "/?#", "]");
                if ((q > p) && at(q, n, ']')) {
                    // look for a "%" scope id
                    int r = scan (p, q, "%");
                    if (r > p) {
                        parseIPv6Reference(p, r);
                        if (r+1 == q) {
                            fail ("scope id expected");
                        }
                        checkChars (r+1, q, L_SCOPE_ID, H_SCOPE_ID,
                                                "scope id");
                    } else {
                        parseIPv6Reference(p, q);
                    }
                    host = input.substring(p-1, q+1);
                    p = q + 1;
                } else {
                    failExpecting("closing bracket for IPv6 address", q);
                }
            } else {
                q = parseIPv4Address(p, n);
                if (q <= p)
                    q = parseHostname(p, n);
                p = q;
            }

            // port
            if (at(p, n, ':')) {
                p++;
                q = scan(p, n, "/");
                if (q > p) {
                    checkChars(p, q, L_DIGIT, H_DIGIT, "port number");
                    try {
                        port = Integer.parseInt(input, p, q, 10);
                    } catch (NumberFormatException x) {
                        fail("Malformed port number", p);
                    }
                    p = q;
                }
            }
            if (p < n)
                failExpecting("port number", p);

            return p;
        }

        // Scan a string of decimal digits whose value fits in a byte
        //
        private int scanByte(int start, int n)
            throws URISyntaxException
        {
            int p = start;
            int q = scan(p, n, L_DIGIT, H_DIGIT);
            if (q <= p) return q;
            if (Integer.parseInt(input, p, q, 10) > 255) return p;
            return q;
        }

        // Scan an IPv4 address.
        //
        // If the strict argument is true then we require that the given
        // interval contain nothing besides an IPv4 address; if it is false
        // then we only require that it start with an IPv4 address.
        //
        // If the interval does not contain or start with (depending upon the
        // strict argument) a legal IPv4 address characters then we return -1
        // immediately; otherwise we insist that these characters parse as a
        // legal IPv4 address and throw an exception on failure.
        //
        // We assume that any string of decimal digits and dots must be an IPv4
        // address.  It won't parse as a hostname anyway, so making that
        // assumption here allows more meaningful exceptions to be thrown.
        //
        private int scanIPv4Address(int start, int n, boolean strict)
            throws URISyntaxException
        {
            int p = start;
            int q;
            int m = scan(p, n, L_DIGIT | L_DOT, H_DIGIT | H_DOT);
            if ((m <= p) || (strict && (m != n)))
                return -1;
            for (;;) {
                // Per RFC2732: At most three digits per byte
                // Further constraint: Each element fits in a byte
                if ((q = scanByte(p, m)) <= p) break;   p = q;
                if ((q = scan(p, m, '.')) <= p) break;  p = q;
                if ((q = scanByte(p, m)) <= p) break;   p = q;
                if ((q = scan(p, m, '.')) <= p) break;  p = q;
                if ((q = scanByte(p, m)) <= p) break;   p = q;
                if ((q = scan(p, m, '.')) <= p) break;  p = q;
                if ((q = scanByte(p, m)) <= p) break;   p = q;
                if (q < m) break;
                return q;
            }
            fail("Malformed IPv4 address", q);
            return -1;
        }

        // Take an IPv4 address: Throw an exception if the given interval
        // contains anything except an IPv4 address
        //
        private int takeIPv4Address(int start, int n, String expected)
            throws URISyntaxException
        {
            int p = scanIPv4Address(start, n, true);
            if (p <= start)
                failExpecting(expected, start);
            return p;
        }

        // Attempt to parse an IPv4 address, returning -1 on failure but
        // allowing the given interval to contain [:<characters>] after
        // the IPv4 address.
        //
        private int parseIPv4Address(int start, int n) {
            int p;

            try {
                p = scanIPv4Address(start, n, false);
            } catch (URISyntaxException x) {
                return -1;
            } catch (NumberFormatException nfe) {
                return -1;
            }

            if (p > start && p < n) {
                // IPv4 address is followed by something - check that
                // it's a ":" as this is the only valid character to
                // follow an address.
                if (input.charAt(p) != ':') {
                    p = -1;
                }
            }

            if (p > start)
                host = input.substring(start, p);

            return p;
        }

        // hostname      = domainlabel [ "." ] | 1*( domainlabel "." ) toplabel [ "." ]
        // domainlabel   = alphanum | alphanum *( alphanum | "-" ) alphanum
        // toplabel      = alpha | alpha *( alphanum | "-" ) alphanum
        //
        private int parseHostname(int start, int n)
            throws URISyntaxException
        {
            int p = start;
            int q;
            int l = -1;                 // Start of last parsed label

            do {
                // domainlabel = alphanum [ *( alphanum | "-" ) alphanum ]
                q = scan(p, n, L_ALPHANUM, H_ALPHANUM);
                if (q <= p)
                    break;
                l = p;
                if (q > p) {
                    p = q;
                    q = scan(p, n, L_ALPHANUM | L_DASH, H_ALPHANUM | H_DASH);
                    if (q > p) {
                        if (input.charAt(q - 1) == '-')
                            fail("Illegal character in hostname", q - 1);
                        p = q;
                    }
                }
                q = scan(p, n, '.');
                if (q <= p)
                    break;
                p = q;
            } while (p < n);

            if ((p < n) && !at(p, n, ':'))
                fail("Illegal character in hostname", p);

            if (l < 0)
                failExpecting("hostname", start);

            // for a fully qualified hostname check that the rightmost
            // label starts with an alpha character.
            if (l > start && !match(input.charAt(l), L_ALPHA, H_ALPHA)) {
                fail("Illegal character in hostname", l);
            }

            host = input.substring(start, p);
            return p;
        }


        // IPv6 address parsing, from RFC2373: IPv6 Addressing Architecture
        //
        // Bug: The grammar in RFC2373 Appendix B does not allow addresses of
        // the form ::12.34.56.78, which are clearly shown in the examples
        // earlier in the document.  Here is the original grammar:
        //
        //   IPv6address = hexpart [ ":" IPv4address ]
        //   hexpart     = hexseq | hexseq "::" [ hexseq ] | "::" [ hexseq ]
        //   hexseq      = hex4 *( ":" hex4)
        //   hex4        = 1*4HEXDIG
        //
        // We therefore use the following revised grammar:
        //
        //   IPv6address = hexseq [ ":" IPv4address ]
        //                 | hexseq [ "::" [ hexpost ] ]
        //                 | "::" [ hexpost ]
        //   hexpost     = hexseq | hexseq ":" IPv4address | IPv4address
        //   hexseq      = hex4 *( ":" hex4)
        //   hex4        = 1*4HEXDIG
        //
        // This covers all and only the following cases:
        //
        //   hexseq
        //   hexseq : IPv4address
        //   hexseq ::
        //   hexseq :: hexseq
        //   hexseq :: hexseq : IPv4address
        //   hexseq :: IPv4address
        //   :: hexseq
        //   :: hexseq : IPv4address
        //   :: IPv4address
        //   ::
        //
        // Additionally we constrain the IPv6 address as follows :-
        //
        //  i.  IPv6 addresses without compressed zeros should contain
        //      exactly 16 bytes.
        //
        //  ii. IPv6 addresses with compressed zeros should contain
        //      less than 16 bytes.

        private int ipv6byteCount = 0;

        private int parseIPv6Reference(int start, int n)
            throws URISyntaxException
        {
            int p = start;
            int q;
            boolean compressedZeros = false;

            q = scanHexSeq(p, n);

            if (q > p) {
                p = q;
                if (at(p, n, "::")) {
                    compressedZeros = true;
                    p = scanHexPost(p + 2, n);
                } else if (at(p, n, ':')) {
                    p = takeIPv4Address(p + 1,  n, "IPv4 address");
                    ipv6byteCount += 4;
                }
            } else if (at(p, n, "::")) {
                compressedZeros = true;
                p = scanHexPost(p + 2, n);
            }
            if (p < n)
                fail("Malformed IPv6 address", start);
            if (ipv6byteCount > 16)
                fail("IPv6 address too long", start);
            if (!compressedZeros && ipv6byteCount < 16)
                fail("IPv6 address too short", start);
            if (compressedZeros && ipv6byteCount == 16)
                fail("Malformed IPv6 address", start);

            return p;
        }

        private int scanHexPost(int start, int n)
            throws URISyntaxException
        {
            int p = start;
            int q;

            if (p == n)
                return p;

            q = scanHexSeq(p, n);
            if (q > p) {
                p = q;
                if (at(p, n, ':')) {
                    p++;
                    p = takeIPv4Address(p, n, "hex digits or IPv4 address");
                    ipv6byteCount += 4;
                }
            } else {
                p = takeIPv4Address(p, n, "hex digits or IPv4 address");
                ipv6byteCount += 4;
            }
            return p;
        }

        // Scan a hex sequence; return -1 if one could not be scanned
        //
        private int scanHexSeq(int start, int n)
            throws URISyntaxException
        {
            int p = start;
            int q;

            q = scan(p, n, L_HEX, H_HEX);
            if (q <= p)
                return -1;
            if (at(q, n, '.'))          // Beginning of IPv4 address
                return -1;
            if (q > p + 4)
                fail("IPv6 hexadecimal digit sequence too long", p);
            ipv6byteCount += 2;
            p = q;
            while (p < n) {
                if (!at(p, n, ':'))
                    break;
                if (at(p + 1, n, ':'))
                    break;              // "::"
                p++;
                q = scan(p, n, L_HEX, H_HEX);
                if (q <= p)
                    failExpecting("digits for an IPv6 address", p);
                if (at(q, n, '.')) {    // Beginning of IPv4 address
                    p--;
                    break;
                }
                if (q > p + 4)
                    fail("IPv6 hexadecimal digit sequence too long", p);
                ipv6byteCount += 2;
                p = q;
            }

            return p;
        }

    }
    static {
        SharedSecrets.setJavaNetUriAccess(
            new JavaNetUriAccess() {
                public URI create(String scheme, String path) {
                    return new URI(scheme, path);
                }
            }
        );
    }
}