https://github.com/google/guava/guava: Guava is a suite of core and expanded libraries that include utility classes, google's collections, io classes, and much much more. 
/*
 * Copyright (C) 2009 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.net;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Ascii;
import com.google.common.base.CharMatcher;
import com.google.common.base.Joiner;
import com.google.common.base.Optional;
import com.google.common.base.Splitter;
import com.google.common.collect.ImmutableList;
import com.google.errorprone.annotations.Immutable;
import com.google.thirdparty.publicsuffix.PublicSuffixPatterns;
import com.google.thirdparty.publicsuffix.PublicSuffixType;
import java.util.List;
import org.checkerframework.checker.nullness.qual.Nullable;


An immutable well-formed internet domain name, such as com or foo.co.uk. Only syntactic analysis is performed; no DNS lookups or other network interactions take place. Thus there is no guarantee that the domain actually exists on the internet. 
One common use of this class is to determine whether a given string is likely to represent an addressable domain on the web -- that is, for a candidate string "xxx", might browsing to "http://xxx/" result in a webpage being displayed? In the past, this test was frequently done by determining whether the domain ended with a public suffix but was not itself a public suffix. However, this test is no longer accurate. There are many domains which are both public suffixes and addressable as hosts; "uk.com" is one example. Using the subset of public suffixes that are registry suffixes, one can get a better result, as only a few registry suffixes are addressable. However, the most useful test to determine if a domain is a plausible web host is hasPublicSuffix(). This will return true for many domains which (currently) are not hosts, such as "com", but given that any public suffix may become a host without warning, it is better to err on the side of permissiveness and thus avoid spurious rejection of valid sites. Of course, to actually determine addressability of any host, clients of this class will need to perform their own DNS lookups. 
During construction, names are normalized in two ways:

    
  
  1. ASCII uppercase characters are converted to lowercase.
  
  2. Unicode dot separators other than the ASCII period ('.') are converted to the ASCII period. 


The normalized values will be returned from toString() and parts(), and will be reflected in the result of equals(Object). 
Internationalized domain
names such as 网络.cn are supported, as are the equivalent IDNA Punycode-encoded
versions.

Author:Catherine Berry
Since:5.0
/**
 * An immutable well-formed internet domain name, such as {@code com} or {@code foo.co.uk}. Only
 * syntactic analysis is performed; no DNS lookups or other network interactions take place. Thus
 * there is no guarantee that the domain actually exists on the internet.
 *
 * <p>One common use of this class is to determine whether a given string is likely to represent an
 * addressable domain on the web -- that is, for a candidate string {@code "xxx"}, might browsing to
 * {@code "http://xxx/"} result in a webpage being displayed? In the past, this test was frequently
 * done by determining whether the domain ended with a {@linkplain #isPublicSuffix() public suffix}
 * but was not itself a public suffix. However, this test is no longer accurate. There are many
 * domains which are both public suffixes and addressable as hosts; {@code "uk.com"} is one example.
 * Using the subset of public suffixes that are {@linkplain #isRegistrySuffix() registry suffixes},
 * one can get a better result, as only a few registry suffixes are addressable. However, the most
 * useful test to determine if a domain is a plausible web host is {@link #hasPublicSuffix()}. This
 * will return {@code true} for many domains which (currently) are not hosts, such as {@code "com"},
 * but given that any public suffix may become a host without warning, it is better to err on the
 * side of permissiveness and thus avoid spurious rejection of valid sites. Of course, to actually
 * determine addressability of any host, clients of this class will need to perform their own DNS
 * lookups.
 *
 * <p>During construction, names are normalized in two ways:
 *
 * <ol>
 *   <li>ASCII uppercase characters are converted to lowercase.
 *   <li>Unicode dot separators other than the ASCII period ({@code '.'}) are converted to the ASCII
 *       period.
 * </ol>
 *
 * <p>The normalized values will be returned from {@link #toString()} and {@link #parts()}, and will
 * be reflected in the result of {@link #equals(Object)}.
 *
 * <p><a href="http://en.wikipedia.org/wiki/Internationalized_domain_name">Internationalized domain
 * names</a> such as {@code 网络.cn} are supported, as are the equivalent <a
 * href="http://en.wikipedia.org/wiki/Internationalized_domain_name">IDNA Punycode-encoded</a>
 * versions.
 *
 * @author Catherine Berry
 * @since 5.0
 */
@Beta
@GwtCompatible
@Immutable
public final class InternetDomainName {

  private static final CharMatcher DOTS_MATCHER = CharMatcher.anyOf(".\u3002\uFF0E\uFF61");
  private static final Splitter DOT_SPLITTER = Splitter.on('.');
  private static final Joiner DOT_JOINER = Joiner.on('.');

  
Value of publicSuffixIndex or registrySuffixIndex which indicates that no relevant suffix was found. 
/**
   * Value of {@link #publicSuffixIndex} or {@link #registrySuffixIndex} which indicates that no
   * relevant suffix was found.
   */
  private static final int NO_SUFFIX_FOUND = -1;

  
Maximum parts (labels) in a domain name. This value arises from the 255-octet limit described
in RFC 2181 part 11 with the fact that the
encoding of each part occupies at least two bytes (dot plus label externally, length byte plus
label internally). Thus, if all labels have the minimum size of one byte, 127 of them will fit.

/**
   * Maximum parts (labels) in a domain name. This value arises from the 255-octet limit described
   * in <a href="http://www.ietf.org/rfc/rfc2181.txt">RFC 2181</a> part 11 with the fact that the
   * encoding of each part occupies at least two bytes (dot plus label externally, length byte plus
   * label internally). Thus, if all labels have the minimum size of one byte, 127 of them will fit.
   */
  private static final int MAX_PARTS = 127;

  
Maximum length of a full domain name, including separators, and leaving room for the root
label. See RFC 2181 part 11.

/**
   * Maximum length of a full domain name, including separators, and leaving room for the root
   * label. See <a href="http://www.ietf.org/rfc/rfc2181.txt">RFC 2181</a> part 11.
   */
  private static final int MAX_LENGTH = 253;

  
Maximum size of a single part of a domain name. See RFC 2181 part 11.

/**
   * Maximum size of a single part of a domain name. See <a
   * href="http://www.ietf.org/rfc/rfc2181.txt">RFC 2181</a> part 11.
   */
  private static final int MAX_DOMAIN_PART_LENGTH = 63;

  
The full domain name, converted to lower case. 
/** The full domain name, converted to lower case. */
  private final String name;

  
The parts of the domain name, converted to lower case. 
/** The parts of the domain name, converted to lower case. */
  private final ImmutableList<String> parts;

  
The index in the parts() list at which the public suffix begins. For example, for the domain name myblog.blogspot.co.uk, the value would be 1 (the index of the 
blogspot part). The value is negative (specifically, NO_SUFFIX_FOUND) if no public suffix was found. 
/**
   * The index in the {@link #parts()} list at which the public suffix begins. For example, for the
   * domain name {@code myblog.blogspot.co.uk}, the value would be 1 (the index of the {@code
   * blogspot} part). The value is negative (specifically, {@link #NO_SUFFIX_FOUND}) if no public
   * suffix was found.
   */
  private final int publicSuffixIndex;

  
The index in the parts() list at which the registry suffix begins. For example, for the domain name myblog.blogspot.co.uk, the value would be 2 (the index of the 
co part). The value is negative (specifically, NO_SUFFIX_FOUND) if no registry suffix was found. 
/**
   * The index in the {@link #parts()} list at which the registry suffix begins. For example, for
   * the domain name {@code myblog.blogspot.co.uk}, the value would be 2 (the index of the {@code
   * co} part). The value is negative (specifically, {@link #NO_SUFFIX_FOUND}) if no registry suffix
   * was found.
   */
  private final int registrySuffixIndex;

  
Constructor used to implement from(String), and from subclasses. 
/** Constructor used to implement {@link #from(String)}, and from subclasses. */
  InternetDomainName(String name) {
    // Normalize:
    // * ASCII characters to lowercase
    // * All dot-like characters to '.'
    // * Strip trailing '.'

    name = Ascii.toLowerCase(DOTS_MATCHER.replaceFrom(name, '.'));

    if (name.endsWith(".")) {
      name = name.substring(0, name.length() - 1);
    }

    checkArgument(name.length() <= MAX_LENGTH, "Domain name too long: '%s':", name);
    this.name = name;

    this.parts = ImmutableList.copyOf(DOT_SPLITTER.split(name));
    checkArgument(parts.size() <= MAX_PARTS, "Domain has too many parts: '%s'", name);
    checkArgument(validateSyntax(parts), "Not a valid domain name: '%s'", name);

    this.publicSuffixIndex = findSuffixOfType(Optional.<PublicSuffixType>absent());
    this.registrySuffixIndex = findSuffixOfType(Optional.of(PublicSuffixType.REGISTRY));
  }

  
Returns the index of the leftmost part of the suffix, or -1 if not found. Note that the value defined as a suffix may not produce true results from isPublicSuffix() or isRegistrySuffix() if the domain ends with an excluded domain pattern such as 
"nhs.uk". 
If a desiredType is specified, this method only finds suffixes of the given type. Otherwise, it finds the first suffix of any type. 
/**
   * Returns the index of the leftmost part of the suffix, or -1 if not found. Note that the value
   * defined as a suffix may not produce {@code true} results from {@link #isPublicSuffix()} or
   * {@link #isRegistrySuffix()} if the domain ends with an excluded domain pattern such as {@code
   * "nhs.uk"}.
   *
   * <p>If a {@code desiredType} is specified, this method only finds suffixes of the given type.
   * Otherwise, it finds the first suffix of any type.
   */
  private int findSuffixOfType(Optional<PublicSuffixType> desiredType) {
    final int partsSize = parts.size();

    for (int i = 0; i < partsSize; i++) {
      String ancestorName = DOT_JOINER.join(parts.subList(i, partsSize));

      if (matchesType(
          desiredType, Optional.fromNullable(PublicSuffixPatterns.EXACT.get(ancestorName)))) {
        return i;
      }

      // Excluded domains (e.g. !nhs.uk) use the next highest
      // domain as the effective public suffix (e.g. uk).

      if (PublicSuffixPatterns.EXCLUDED.containsKey(ancestorName)) {
        return i + 1;
      }

      if (matchesWildcardSuffixType(desiredType, ancestorName)) {
        return i;
      }
    }

    return NO_SUFFIX_FOUND;
  }

  
Returns an instance of InternetDomainName after lenient validation. Specifically, validation against RFC 3490
("Internationalizing Domain Names in Applications") is skipped, while validation against RFC 1035 is relaxed in the following ways:

    
  
  • Any part containing non-ASCII characters is considered valid.
  
  • Underscores ('_') are permitted wherever dashes ('-') are permitted.
  
  • Parts other than the final part may start with a digit, as mandated by RFC 1123.



Params:
  • domain – A domain name (not IP address)
Throws:
Since:10.0 (previously named fromLenient)
/**
   * Returns an instance of {@link InternetDomainName} after lenient validation. Specifically,
   * validation against <a href="http://www.ietf.org/rfc/rfc3490.txt">RFC 3490</a>
   * ("Internationalizing Domain Names in Applications") is skipped, while validation against <a
   * href="http://www.ietf.org/rfc/rfc1035.txt">RFC 1035</a> is relaxed in the following ways:
   *
   * <ul>
   *   <li>Any part containing non-ASCII characters is considered valid.
   *   <li>Underscores ('_') are permitted wherever dashes ('-') are permitted.
   *   <li>Parts other than the final part may start with a digit, as mandated by <a
   *       href="https://tools.ietf.org/html/rfc1123#section-2">RFC 1123</a>.
   * </ul>
   *
   *
   * @param domain A domain name (not IP address)
   * @throws IllegalArgumentException if {@code domain} is not syntactically valid according to
   *     {@link #isValid}
   * @since 10.0 (previously named {@code fromLenient})
   */
  public static InternetDomainName from(String domain) {
    return new InternetDomainName(checkNotNull(domain));
  }

  
Validation method used by from to ensure that the domain name is syntactically valid according to RFC 1035. 
Returns:Is the domain name syntactically valid?
/**
   * Validation method used by {@code from} to ensure that the domain name is syntactically valid
   * according to RFC 1035.
   *
   * @return Is the domain name syntactically valid?
   */
  private static boolean validateSyntax(List<String> parts) {
    final int lastIndex = parts.size() - 1;

    // Validate the last part specially, as it has different syntax rules.

    if (!validatePart(parts.get(lastIndex), true)) {
      return false;
    }

    for (int i = 0; i < lastIndex; i++) {
      String part = parts.get(i);
      if (!validatePart(part, false)) {
        return false;
      }
    }

    return true;
  }

  private static final CharMatcher DASH_MATCHER = CharMatcher.anyOf("-_");

  private static final CharMatcher PART_CHAR_MATCHER =
      CharMatcher.javaLetterOrDigit().or(DASH_MATCHER);

  
Helper method for validateSyntax(List<String>). Validates that one part of a domain name is valid. 
Params:
  • part – The domain name part to be validated
  • isFinalPart – Is this the final (rightmost) domain part?
Returns:Whether the part is valid
/**
   * Helper method for {@link #validateSyntax(List)}. Validates that one part of a domain name is
   * valid.
   *
   * @param part The domain name part to be validated
   * @param isFinalPart Is this the final (rightmost) domain part?
   * @return Whether the part is valid
   */
  private static boolean validatePart(String part, boolean isFinalPart) {

    // These tests could be collapsed into one big boolean expression, but
    // they have been left as independent tests for clarity.

    if (part.length() < 1 || part.length() > MAX_DOMAIN_PART_LENGTH) {
      return false;
    }

    /*
     * GWT claims to support java.lang.Character's char-classification methods, but it actually only
     * works for ASCII. So for now, assume any non-ASCII characters are valid. The only place this
     * seems to be documented is here:
     * http://osdir.com/ml/GoogleWebToolkitContributors/2010-03/msg00178.html
     *
     * <p>ASCII characters in the part are expected to be valid per RFC 1035, with underscore also
     * being allowed due to widespread practice.
     */

    String asciiChars = CharMatcher.ascii().retainFrom(part);

    if (!PART_CHAR_MATCHER.matchesAllOf(asciiChars)) {
      return false;
    }

    // No initial or final dashes or underscores.

    if (DASH_MATCHER.matches(part.charAt(0))
        || DASH_MATCHER.matches(part.charAt(part.length() - 1))) {
      return false;
    }

    /*
     * Note that we allow (in contravention of a strict interpretation of the relevant RFCs) domain
     * parts other than the last may begin with a digit (for example, "3com.com"). It's important to
     * disallow an initial digit in the last part; it's the only thing that stops an IPv4 numeric
     * address like 127.0.0.1 from looking like a valid domain name.
     */

    if (isFinalPart && CharMatcher.digit().matches(part.charAt(0))) {
      return false;
    }

    return true;
  }

  
Returns the individual components of this domain name, normalized to all lower case. For example, for the domain name mail.google.com, this method returns the list 
["mail", "google", "com"]. 
/**
   * Returns the individual components of this domain name, normalized to all lower case. For
   * example, for the domain name {@code mail.google.com}, this method returns the list {@code
   * ["mail", "google", "com"]}.
   */
  public ImmutableList<String> parts() {
    return parts;
  }

  
Indicates whether this domain name represents a public suffix, as defined by the Mozilla
Foundation's Public Suffix List (PSL). A public suffix is one under which Internet users can directly register names, such as com, 
co.uk or pvt.k12.wy.us. Examples of domain names that are not public suffixes include google.com, foo.co.uk, and myblog.blogspot.com. 
Public suffixes are a proper superset of registry suffixes. The list of public suffixes additionally contains privately owned domain names under which Internet users can register subdomains. An example of a public suffix that is not a registry suffix is blogspot.com. Note that it is true that all public suffixes have
registry suffixes, since domain name registries collectively control all internet domain names.

For considerations on whether the public suffix or registry suffix designation is more
suitable for your application, see this article.

Returns:true if this domain name appears exactly on the public suffix list
Since:6.0
/**
   * Indicates whether this domain name represents a <i>public suffix</i>, as defined by the Mozilla
   * Foundation's <a href="http://publicsuffix.org/">Public Suffix List</a> (PSL). A public suffix
   * is one under which Internet users can directly register names, such as {@code com}, {@code
   * co.uk} or {@code pvt.k12.wy.us}. Examples of domain names that are <i>not</i> public suffixes
   * include {@code google.com}, {@code foo.co.uk}, and {@code myblog.blogspot.com}.
   *
   * <p>Public suffixes are a proper superset of {@linkplain #isRegistrySuffix() registry suffixes}.
   * The list of public suffixes additionally contains privately owned domain names under which
   * Internet users can register subdomains. An example of a public suffix that is not a registry
   * suffix is {@code blogspot.com}. Note that it is true that all public suffixes <i>have</i>
   * registry suffixes, since domain name registries collectively control all internet domain names.
   *
   * <p>For considerations on whether the public suffix or registry suffix designation is more
   * suitable for your application, see <a
   * href="https://github.com/google/guava/wiki/InternetDomainNameExplained">this article</a>.
   *
   * @return {@code true} if this domain name appears exactly on the public suffix list
   * @since 6.0
   */
  public boolean isPublicSuffix() {
    return publicSuffixIndex == 0;
  }

  
Indicates whether this domain name ends in a public suffix, including if it is a public suffix itself. For example, returns true for 
www.google.com, foo.co.uk and com, but not for invalid or 
google.invalid. This is the recommended method for determining whether a domain is potentially an addressable host. 
Note that this method is equivalent to hasRegistrySuffix() because all registry suffixes are public suffixes and all public suffixes have registry suffixes.

Since:6.0
/**
   * Indicates whether this domain name ends in a {@linkplain #isPublicSuffix() public suffix},
   * including if it is a public suffix itself. For example, returns {@code true} for {@code
   * www.google.com}, {@code foo.co.uk} and {@code com}, but not for {@code invalid} or {@code
   * google.invalid}. This is the recommended method for determining whether a domain is potentially
   * an addressable host.
   *
   * <p>Note that this method is equivalent to {@link #hasRegistrySuffix()} because all registry
   * suffixes are public suffixes <i>and</i> all public suffixes have registry suffixes.
   *
   * @since 6.0
   */
  public boolean hasPublicSuffix() {
    return publicSuffixIndex != NO_SUFFIX_FOUND;
  }

  
Returns the public suffix portion of the domain name, or 
null if no public suffix is present. 
Since:6.0
/**
   * Returns the {@linkplain #isPublicSuffix() public suffix} portion of the domain name, or {@code
   * null} if no public suffix is present.
   *
   * @since 6.0
   */
  public InternetDomainName publicSuffix() {
    return hasPublicSuffix() ? ancestor(publicSuffixIndex) : null;
  }

  
Indicates whether this domain name ends in a public suffix, while not being a public suffix itself. For example, returns true for 
www.google.com, foo.co.uk and myblog.blogspot.com, but not for com, co.uk, google.invalid, or blogspot.com. 
This method can be used to determine whether it will probably be possible to set cookies on
the domain, though even that depends on individual browsers' implementations of cookie
controls. See RFC 2109 for details.

Since:6.0
/**
   * Indicates whether this domain name ends in a {@linkplain #isPublicSuffix() public suffix},
   * while not being a public suffix itself. For example, returns {@code true} for {@code
   * www.google.com}, {@code foo.co.uk} and {@code myblog.blogspot.com}, but not for {@code com},
   * {@code co.uk}, {@code google.invalid}, or {@code blogspot.com}.
   *
   * <p>This method can be used to determine whether it will probably be possible to set cookies on
   * the domain, though even that depends on individual browsers' implementations of cookie
   * controls. See <a href="http://www.ietf.org/rfc/rfc2109.txt">RFC 2109</a> for details.
   *
   * @since 6.0
   */
  public boolean isUnderPublicSuffix() {
    return publicSuffixIndex > 0;
  }

  
Indicates whether this domain name is composed of exactly one subdomain component followed by a public suffix. For example, returns true for 
google.com foo.co.uk, and myblog.blogspot.com, but not for 
www.google.com, co.uk, or blogspot.com. 
This method can be used to determine whether a domain is probably the highest level for
which cookies may be set, though even that depends on individual browsers' implementations of
cookie controls. See RFC 2109 for details.

Since:6.0
/**
   * Indicates whether this domain name is composed of exactly one subdomain component followed by a
   * {@linkplain #isPublicSuffix() public suffix}. For example, returns {@code true} for {@code
   * google.com} {@code foo.co.uk}, and {@code myblog.blogspot.com}, but not for {@code
   * www.google.com}, {@code co.uk}, or {@code blogspot.com}.
   *
   * <p>This method can be used to determine whether a domain is probably the highest level for
   * which cookies may be set, though even that depends on individual browsers' implementations of
   * cookie controls. See <a href="http://www.ietf.org/rfc/rfc2109.txt">RFC 2109</a> for details.
   *
   * @since 6.0
   */
  public boolean isTopPrivateDomain() {
    return publicSuffixIndex == 1;
  }

  
Returns the portion of this domain name that is one level beneath the public suffix. For example, for x.adwords.google.co.uk it returns google.co.uk, since co.uk is a public suffix. Similarly, for 
myblog.blogspot.com it returns the same domain, myblog.blogspot.com, since 
blogspot.com is a public suffix. 
If isTopPrivateDomain() is true, the current domain name instance is returned. 
This method can be used to determine the probable highest level parent domain for which
cookies may be set, though even that depends on individual browsers' implementations of cookie
controls.

Throws:
Since:6.0
/**
   * Returns the portion of this domain name that is one level beneath the {@linkplain
   * #isPublicSuffix() public suffix}. For example, for {@code x.adwords.google.co.uk} it returns
   * {@code google.co.uk}, since {@code co.uk} is a public suffix. Similarly, for {@code
   * myblog.blogspot.com} it returns the same domain, {@code myblog.blogspot.com}, since {@code
   * blogspot.com} is a public suffix.
   *
   * <p>If {@link #isTopPrivateDomain()} is true, the current domain name instance is returned.
   *
   * <p>This method can be used to determine the probable highest level parent domain for which
   * cookies may be set, though even that depends on individual browsers' implementations of cookie
   * controls.
   *
   * @throws IllegalStateException if this domain does not end with a public suffix
   * @since 6.0
   */
  public InternetDomainName topPrivateDomain() {
    if (isTopPrivateDomain()) {
      return this;
    }
    checkState(isUnderPublicSuffix(), "Not under a public suffix: %s", name);
    return ancestor(publicSuffixIndex - 1);
  }

  
Indicates whether this domain name represents a registry suffix, as defined by a subset
of the Mozilla Foundation's Public Suffix List (PSL). A registry suffix is one under which Internet users can directly register names via a domain name registrar, and have such registrations lawfully protected by internet-governing bodies such as ICANN. Examples of registry suffixes include com, co.uk, and 
pvt.k12.wy.us. Examples of domain names that are not registry suffixes include 
google.com and foo.co.uk. 
Registry suffixes are a proper subset of public suffixes. The list of public suffixes additionally contains privately owned domain names under which Internet users can register subdomains. An example of a public suffix that is not a registry suffix is blogspot.com. Note that it is true that all public suffixes have registry
suffixes, since domain name registries collectively control all internet domain names.

For considerations on whether the public suffix or registry suffix designation is more
suitable for your application, see this article.

Returns:true if this domain name appears exactly on the public suffix list as part of the registry suffix section (labelled "ICANN").
Since:23.3
/**
   * Indicates whether this domain name represents a <i>registry suffix</i>, as defined by a subset
   * of the Mozilla Foundation's <a href="http://publicsuffix.org/">Public Suffix List</a> (PSL). A
   * registry suffix is one under which Internet users can directly register names via a domain name
   * registrar, and have such registrations lawfully protected by internet-governing bodies such as
   * ICANN. Examples of registry suffixes include {@code com}, {@code co.uk}, and {@code
   * pvt.k12.wy.us}. Examples of domain names that are <i>not</i> registry suffixes include {@code
   * google.com} and {@code foo.co.uk}.
   *
   * <p>Registry suffixes are a proper subset of {@linkplain #isPublicSuffix() public suffixes}. The
   * list of public suffixes additionally contains privately owned domain names under which Internet
   * users can register subdomains. An example of a public suffix that is not a registry suffix is
   * {@code blogspot.com}. Note that it is true that all public suffixes <i>have</i> registry
   * suffixes, since domain name registries collectively control all internet domain names.
   *
   * <p>For considerations on whether the public suffix or registry suffix designation is more
   * suitable for your application, see <a
   * href="https://github.com/google/guava/wiki/InternetDomainNameExplained">this article</a>.
   *
   * @return {@code true} if this domain name appears exactly on the public suffix list as part of
   *     the registry suffix section (labelled "ICANN").
   * @since 23.3
   */
  public boolean isRegistrySuffix() {
    return registrySuffixIndex == 0;
  }

  
Indicates whether this domain name ends in a registry suffix, including if it is a registry suffix itself. For example, returns true for 
www.google.com, foo.co.uk and com, but not for invalid or 
google.invalid. 
Note that this method is equivalent to hasPublicSuffix() because all registry suffixes are public suffixes and all public suffixes have registry suffixes.

Since:23.3
/**
   * Indicates whether this domain name ends in a {@linkplain #isRegistrySuffix() registry suffix},
   * including if it is a registry suffix itself. For example, returns {@code true} for {@code
   * www.google.com}, {@code foo.co.uk} and {@code com}, but not for {@code invalid} or {@code
   * google.invalid}.
   *
   * <p>Note that this method is equivalent to {@link #hasPublicSuffix()} because all registry
   * suffixes are public suffixes <i>and</i> all public suffixes have registry suffixes.
   *
   * @since 23.3
   */
  public boolean hasRegistrySuffix() {
    return registrySuffixIndex != NO_SUFFIX_FOUND;
  }

  
Returns the registry suffix portion of the domain name, or null if no registry suffix is present. 
Since:23.3
/**
   * Returns the {@linkplain #isRegistrySuffix() registry suffix} portion of the domain name, or
   * {@code null} if no registry suffix is present.
   *
   * @since 23.3
   */
  public InternetDomainName registrySuffix() {
    return hasRegistrySuffix() ? ancestor(registrySuffixIndex) : null;
  }

  
Indicates whether this domain name ends in a registry suffix, while not being a registry suffix itself. For example, returns true for 
www.google.com, foo.co.uk and blogspot.com, but not for com, 
co.uk, or google.invalid. 
Since:23.3
/**
   * Indicates whether this domain name ends in a {@linkplain #isRegistrySuffix() registry suffix},
   * while not being a registry suffix itself. For example, returns {@code true} for {@code
   * www.google.com}, {@code foo.co.uk} and {@code blogspot.com}, but not for {@code com}, {@code
   * co.uk}, or {@code google.invalid}.
   *
   * @since 23.3
   */
  public boolean isUnderRegistrySuffix() {
    return registrySuffixIndex > 0;
  }

  
Indicates whether this domain name is composed of exactly one subdomain component followed by a registry suffix. For example, returns true for 
google.com, foo.co.uk, and blogspot.com, but not for www.google.com, co.uk, or myblog.blogspot.com. 
Warning: This method should not be used to determine the probable highest level parent domain for which cookies may be set. Use topPrivateDomain() for that purpose. 
Since:23.3
/**
   * Indicates whether this domain name is composed of exactly one subdomain component followed by a
   * {@linkplain #isRegistrySuffix() registry suffix}. For example, returns {@code true} for {@code
   * google.com}, {@code foo.co.uk}, and {@code blogspot.com}, but not for {@code www.google.com},
   * {@code co.uk}, or {@code myblog.blogspot.com}.
   *
   * <p><b>Warning:</b> This method should not be used to determine the probable highest level
   * parent domain for which cookies may be set. Use {@link #topPrivateDomain()} for that purpose.
   *
   * @since 23.3
   */
  public boolean isTopDomainUnderRegistrySuffix() {
    return registrySuffixIndex == 1;
  }

  
Returns the portion of this domain name that is one level beneath the registry suffix. For example, for x.adwords.google.co.uk it returns google.co.uk, since co.uk is a registry suffix. Similarly, for 
myblog.blogspot.com it returns blogspot.com, since com is a registry suffix. 
If isTopDomainUnderRegistrySuffix() is true, the current domain name instance is returned. 
Warning: This method should not be used to determine whether a domain is probably the highest level for which cookies may be set. Use isTopPrivateDomain() for that purpose. 
Throws:
Since:23.3
/**
   * Returns the portion of this domain name that is one level beneath the {@linkplain
   * #isRegistrySuffix() registry suffix}. For example, for {@code x.adwords.google.co.uk} it
   * returns {@code google.co.uk}, since {@code co.uk} is a registry suffix. Similarly, for {@code
   * myblog.blogspot.com} it returns {@code blogspot.com}, since {@code com} is a registry suffix.
   *
   * <p>If {@link #isTopDomainUnderRegistrySuffix()} is true, the current domain name instance is
   * returned.
   *
   * <p><b>Warning:</b> This method should not be used to determine whether a domain is probably the
   * highest level for which cookies may be set. Use {@link #isTopPrivateDomain()} for that purpose.
   *
   * @throws IllegalStateException if this domain does not end with a registry suffix
   * @since 23.3
   */
  public InternetDomainName topDomainUnderRegistrySuffix() {
    if (isTopDomainUnderRegistrySuffix()) {
      return this;
    }
    checkState(isUnderRegistrySuffix(), "Not under a registry suffix: %s", name);
    return ancestor(registrySuffixIndex - 1);
  }

  
Indicates whether this domain is composed of two or more parts. 
/** Indicates whether this domain is composed of two or more parts. */
  public boolean hasParent() {
    return parts.size() > 1;
  }

  
Returns an InternetDomainName that is the immediate ancestor of this one; that is, the current domain with the leftmost part removed. For example, the parent of 
www.google.com is google.com. 
Throws:
/**
   * Returns an {@code InternetDomainName} that is the immediate ancestor of this one; that is, the
   * current domain with the leftmost part removed. For example, the parent of {@code
   * www.google.com} is {@code google.com}.
   *
   * @throws IllegalStateException if the domain has no parent, as determined by {@link #hasParent}
   */
  public InternetDomainName parent() {
    checkState(hasParent(), "Domain '%s' has no parent", name);
    return ancestor(1);
  }

  
Returns the ancestor of the current domain at the given number of levels "higher" (rightward) in the subdomain list. The number of levels must be non-negative, and less than N-1, where N is the number of parts in the domain. 
TODO: Reasonable candidate for addition to public API.

/**
   * Returns the ancestor of the current domain at the given number of levels "higher" (rightward)
   * in the subdomain list. The number of levels must be non-negative, and less than {@code N-1},
   * where {@code N} is the number of parts in the domain.
   *
   * <p>TODO: Reasonable candidate for addition to public API.
   */
  private InternetDomainName ancestor(int levels) {
    return from(DOT_JOINER.join(parts.subList(levels, parts.size())));
  }

  
Creates and returns a new InternetDomainName by prepending the argument and a dot to the current name. For example, InternetDomainName.from("foo.com").child("www.bar") returns a new InternetDomainName with the value www.bar.foo.com. Only lenient validation is performed, as described here. 
Throws:
/**
   * Creates and returns a new {@code InternetDomainName} by prepending the argument and a dot to
   * the current name. For example, {@code InternetDomainName.from("foo.com").child("www.bar")}
   * returns a new {@code InternetDomainName} with the value {@code www.bar.foo.com}. Only lenient
   * validation is performed, as described {@link #from(String) here}.
   *
   * @throws NullPointerException if leftParts is null
   * @throws IllegalArgumentException if the resulting name is not valid
   */
  public InternetDomainName child(String leftParts) {
    return from(checkNotNull(leftParts) + "." + name);
  }

  
Indicates whether the argument is a syntactically valid domain name using lenient validation.
Specifically, validation against RFC 3490
("Internationalizing Domain Names in Applications") is skipped.

The following two code snippets are equivalent:


domainName = InternetDomainName.isValid(name)
    ? InternetDomainName.from(name)
    : DEFAULT_DOMAIN;




try {
  domainName = InternetDomainName.from(name);
 } catch (IllegalArgumentException e) {
  domainName = DEFAULT_DOMAIN;
 }



Since:8.0 (previously named isValidLenient)
/**
   * Indicates whether the argument is a syntactically valid domain name using lenient validation.
   * Specifically, validation against <a href="http://www.ietf.org/rfc/rfc3490.txt">RFC 3490</a>
   * ("Internationalizing Domain Names in Applications") is skipped.
   *
   * <p>The following two code snippets are equivalent:
   *
   * <pre>{@code
   * domainName = InternetDomainName.isValid(name)
   *     ? InternetDomainName.from(name)
   *     : DEFAULT_DOMAIN;
   * }</pre>
   *
   * <pre>{@code
   * try {
   *   domainName = InternetDomainName.from(name);
   * } catch (IllegalArgumentException e) {
   *   domainName = DEFAULT_DOMAIN;
   * }
   * }</pre>
   *
   * @since 8.0 (previously named {@code isValidLenient})
   */
  public static boolean isValid(String name) {
    try {
      from(name);
      return true;
    } catch (IllegalArgumentException e) {
      return false;
    }
  }

  
Does the domain name match one of the "wildcard" patterns (e.g. "*.ar")? If a 
desiredType is specified, the wildcard pattern must also match that type. 
/**
   * Does the domain name match one of the "wildcard" patterns (e.g. {@code "*.ar"})? If a {@code
   * desiredType} is specified, the wildcard pattern must also match that type.
   */
  private static boolean matchesWildcardSuffixType(
      Optional<PublicSuffixType> desiredType, String domain) {
    List<String> pieces = DOT_SPLITTER.limit(2).splitToList(domain);
    return pieces.size() == 2
        && matchesType(
            desiredType, Optional.fromNullable(PublicSuffixPatterns.UNDER.get(pieces.get(1))));
  }

  
If a desiredType is specified, returns true only if the actualType is identical. Otherwise, returns true as long as actualType is present. 
/**
   * If a {@code desiredType} is specified, returns true only if the {@code actualType} is
   * identical. Otherwise, returns true as long as {@code actualType} is present.
   */
  private static boolean matchesType(
      Optional<PublicSuffixType> desiredType, Optional<PublicSuffixType> actualType) {
    return desiredType.isPresent() ? desiredType.equals(actualType) : actualType.isPresent();
  }

  
Returns the domain name, normalized to all lower case. 
/** Returns the domain name, normalized to all lower case. */
  @Override
  public String toString() {
    return name;
  }

  
Equality testing is based on the text supplied by the caller, after normalization as described
in the class documentation. For example, a non-ASCII Unicode domain name and the Punycode
version of the same domain name would not be considered equal.

/**
   * Equality testing is based on the text supplied by the caller, after normalization as described
   * in the class documentation. For example, a non-ASCII Unicode domain name and the Punycode
   * version of the same domain name would not be considered equal.
   */
  @Override
  public boolean equals(@Nullable Object object) {
    if (object == this) {
      return true;
    }

    if (object instanceof InternetDomainName) {
      InternetDomainName that = (InternetDomainName) object;
      return this.name.equals(that.name);
    }

    return false;
  }

  @Override
  public int hashCode() {
    return name.hashCode();
  }
}