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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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package java.io;

import java.net.URI;
import java.net.URL;
import java.net.MalformedURLException;
import java.net.URISyntaxException;
import java.util.List;
import java.util.ArrayList;
import java.security.SecureRandom;
import java.nio.file.Path;
import java.nio.file.FileSystems;
import sun.security.action.GetPropertyAction;

An abstract representation of file and directory pathnames.
 User interfaces and operating systems use system-dependent pathname
strings to name files and directories.  This class presents an
abstract, system-independent view of hierarchical pathnames.  An
abstract pathname has two components:

 An optional system-dependent prefix string,
     such as a disk-drive specifier, "/" for the UNIX root
     directory, or "\\\\" for a Microsoft Windows UNC pathname, and
 A sequence of zero or more string names.

The first name in an abstract pathname may be a directory name or, in the
case of Microsoft Windows UNC pathnames, a hostname.  Each subsequent name
in an abstract pathname denotes a directory; the last name may denote
either a directory or a file.  The empty abstract pathname has no
prefix and an empty name sequence.
 The conversion of a pathname string to or from an abstract pathname is
inherently system-dependent.  When an abstract pathname is converted into a
pathname string, each name is separated from the next by a single copy of
the default separator character.  The default name-separator
character is defined by the system property file.separator, and is made available in the public static fields separator and separatorChar of this class. When a pathname string is converted into an abstract pathname, the names within it may be separated by the default name-separator character or by any other name-separator character that is supported by the underlying system. 
 A pathname, whether abstract or in string form, may be either
absolute or relative.  An absolute pathname is complete in
that no other information is required in order to locate the file that it
denotes.  A relative pathname, in contrast, must be interpreted in terms of
information taken from some other pathname.  By default the classes in the
java.io package always resolve relative pathnames against the
current user directory.  This directory is named by the system property
user.dir, and is typically the directory in which the Java
virtual machine was invoked.
 The parent of an abstract pathname may be obtained by invoking the getParent method of this class and consists of the pathname's prefix and each name in the pathname's name sequence except for the last. Each directory's absolute pathname is an ancestor of any File object with an absolute abstract pathname which begins with the directory's absolute pathname. For example, the directory denoted by the abstract pathname "/usr" is an ancestor of the directory denoted by the pathname "/usr/local/bin". 
 The prefix concept is used to handle root directories on UNIX platforms,
and drive specifiers, root directories and UNC pathnames on Microsoft Windows platforms,
as follows:

 For UNIX platforms, the prefix of an absolute pathname is always
"/".  Relative pathnames have no prefix.  The abstract pathname
denoting the root directory has the prefix "/" and an empty
name sequence.
 For Microsoft Windows platforms, the prefix of a pathname that contains a drive
specifier consists of the drive letter followed by ":" and
possibly followed by "\\" if the pathname is absolute.  The
prefix of a UNC pathname is "\\\\"; the hostname and the share
name are the first two names in the name sequence.  A relative pathname that
does not specify a drive has no prefix.

 Instances of this class may or may not denote an actual file-system
object such as a file or a directory.  If it does denote such an object
then that object resides in a partition.  A partition is an
operating system-specific portion of storage for a file system.  A single
storage device (e.g. a physical disk-drive, flash memory, CD-ROM) may
contain multiple partitions.  The object, if any, will reside on the
partition named by some ancestor of the absolute
form of this pathname.
 A file system may implement restrictions to certain operations on the
actual file-system object, such as reading, writing, and executing.  These
restrictions are collectively known as access permissions.  The file
system may have multiple sets of access permissions on a single object.
For example, one set may apply to the object's owner, and another
may apply to all other users.  The access permissions on an object may
cause some methods in this class to fail.
 Instances of the File class are immutable; that is, once
created, the abstract pathname represented by a File object
will never change.
Interoperability with java.nio.file package
 The java.nio.file package defines interfaces and classes for the Java virtual machine to access files, file attributes, and file systems. This API may be used to overcome many of the limitations of the java.io.File class. The toPath method may be used to obtain a Path that uses the abstract path represented by a File object to locate a file. The resulting Path may be used with the Files class to provide more efficient and extensive access to additional file operations, file attributes, and I/O exceptions to help diagnose errors when an operation on a file fails. 
Author:
 unascribed
Since:
  1.0/**
 * An abstract representation of file and directory pathnames.
 *
 * <p> User interfaces and operating systems use system-dependent <em>pathname
 * strings</em> to name files and directories.  This class presents an
 * abstract, system-independent view of hierarchical pathnames.  An
 * <em>abstract pathname</em> has two components:
 *
 * <ol>
 * <li> An optional system-dependent <em>prefix</em> string,
 *      such as a disk-drive specifier, <code>"/"</code>&nbsp;for the UNIX root
 *      directory, or <code>"\\\\"</code>&nbsp;for a Microsoft Windows UNC pathname, and
 * <li> A sequence of zero or more string <em>names</em>.
 * </ol>
 *
 * The first name in an abstract pathname may be a directory name or, in the
 * case of Microsoft Windows UNC pathnames, a hostname.  Each subsequent name
 * in an abstract pathname denotes a directory; the last name may denote
 * either a directory or a file.  The <em>empty</em> abstract pathname has no
 * prefix and an empty name sequence.
 *
 * <p> The conversion of a pathname string to or from an abstract pathname is
 * inherently system-dependent.  When an abstract pathname is converted into a
 * pathname string, each name is separated from the next by a single copy of
 * the default <em>separator character</em>.  The default name-separator
 * character is defined by the system property <code>file.separator</code>, and
 * is made available in the public static fields {@link
 * #separator} and {@link #separatorChar} of this class.
 * When a pathname string is converted into an abstract pathname, the names
 * within it may be separated by the default name-separator character or by any
 * other name-separator character that is supported by the underlying system.
 *
 * <p> A pathname, whether abstract or in string form, may be either
 * <em>absolute</em> or <em>relative</em>.  An absolute pathname is complete in
 * that no other information is required in order to locate the file that it
 * denotes.  A relative pathname, in contrast, must be interpreted in terms of
 * information taken from some other pathname.  By default the classes in the
 * <code>java.io</code> package always resolve relative pathnames against the
 * current user directory.  This directory is named by the system property
 * <code>user.dir</code>, and is typically the directory in which the Java
 * virtual machine was invoked.
 *
 * <p> The <em>parent</em> of an abstract pathname may be obtained by invoking
 * the {@link #getParent} method of this class and consists of the pathname's
 * prefix and each name in the pathname's name sequence except for the last.
 * Each directory's absolute pathname is an ancestor of any {@code File}
 * object with an absolute abstract pathname which begins with the directory's
 * absolute pathname.  For example, the directory denoted by the abstract
 * pathname {@code "/usr"} is an ancestor of the directory denoted by the
 * pathname {@code "/usr/local/bin"}.
 *
 * <p> The prefix concept is used to handle root directories on UNIX platforms,
 * and drive specifiers, root directories and UNC pathnames on Microsoft Windows platforms,
 * as follows:
 *
 * <ul>
 *
 * <li> For UNIX platforms, the prefix of an absolute pathname is always
 * <code>"/"</code>.  Relative pathnames have no prefix.  The abstract pathname
 * denoting the root directory has the prefix <code>"/"</code> and an empty
 * name sequence.
 *
 * <li> For Microsoft Windows platforms, the prefix of a pathname that contains a drive
 * specifier consists of the drive letter followed by <code>":"</code> and
 * possibly followed by <code>"\\"</code> if the pathname is absolute.  The
 * prefix of a UNC pathname is <code>"\\\\"</code>; the hostname and the share
 * name are the first two names in the name sequence.  A relative pathname that
 * does not specify a drive has no prefix.
 *
 * </ul>
 *
 * <p> Instances of this class may or may not denote an actual file-system
 * object such as a file or a directory.  If it does denote such an object
 * then that object resides in a <i>partition</i>.  A partition is an
 * operating system-specific portion of storage for a file system.  A single
 * storage device (e.g. a physical disk-drive, flash memory, CD-ROM) may
 * contain multiple partitions.  The object, if any, will reside on the
 * partition <a id="partName">named</a> by some ancestor of the absolute
 * form of this pathname.
 *
 * <p> A file system may implement restrictions to certain operations on the
 * actual file-system object, such as reading, writing, and executing.  These
 * restrictions are collectively known as <i>access permissions</i>.  The file
 * system may have multiple sets of access permissions on a single object.
 * For example, one set may apply to the object's <i>owner</i>, and another
 * may apply to all other users.  The access permissions on an object may
 * cause some methods in this class to fail.
 *
 * <p> Instances of the <code>File</code> class are immutable; that is, once
 * created, the abstract pathname represented by a <code>File</code> object
 * will never change.
 *
 * <h3>Interoperability with {@code java.nio.file} package</h3>
 *
 * <p> The <a href="../../java/nio/file/package-summary.html">{@code java.nio.file}</a>
 * package defines interfaces and classes for the Java virtual machine to access
 * files, file attributes, and file systems. This API may be used to overcome
 * many of the limitations of the {@code java.io.File} class.
 * The {@link #toPath toPath} method may be used to obtain a {@link
 * Path} that uses the abstract path represented by a {@code File} object to
 * locate a file. The resulting {@code Path} may be used with the {@link
 * java.nio.file.Files} class to provide more efficient and extensive access to
 * additional file operations, file attributes, and I/O exceptions to help
 * diagnose errors when an operation on a file fails.
 *
 * @author  unascribed
 * @since   1.0
 */

public class File
    implements Serializable, Comparable<File>
{

    
The FileSystem object representing the platform's local file system.
/**
     * The FileSystem object representing the platform's local file system.
     */
    private static final FileSystem fs = DefaultFileSystem.getFileSystem();

    
This abstract pathname's normalized pathname string. A normalized
pathname string uses the default name-separator character and does not
contain any duplicate or redundant separators.
@serial
/**
     * This abstract pathname's normalized pathname string. A normalized
     * pathname string uses the default name-separator character and does not
     * contain any duplicate or redundant separators.
     *
     * @serial
     */
    private final String path;

    
Enum type that indicates the status of a file path.
/**
     * Enum type that indicates the status of a file path.
     */
    private static enum PathStatus { INVALID, CHECKED };

    
The flag indicating whether the file path is invalid.
/**
     * The flag indicating whether the file path is invalid.
     */
    private transient PathStatus status = null;

    
Check if the file has an invalid path. Currently, the inspection of
a file path is very limited, and it only covers Nul character check.
Returning true means the path is definitely invalid/garbage. But
returning false does not guarantee that the path is valid.
Returns:
true if the file path is invalid./**
     * Check if the file has an invalid path. Currently, the inspection of
     * a file path is very limited, and it only covers Nul character check.
     * Returning true means the path is definitely invalid/garbage. But
     * returning false does not guarantee that the path is valid.
     *
     * @return true if the file path is invalid.
     */
    final boolean isInvalid() {
        if (status == null) {
            status = (this.path.indexOf('\u0000') < 0) ? PathStatus.CHECKED
                                                       : PathStatus.INVALID;
        }
        return status == PathStatus.INVALID;
    }

    
The length of this abstract pathname's prefix, or zero if it has no
prefix.
/**
     * The length of this abstract pathname's prefix, or zero if it has no
     * prefix.
     */
    private final transient int prefixLength;

    
Returns the length of this abstract pathname's prefix.
For use by FileSystem classes.
/**
     * Returns the length of this abstract pathname's prefix.
     * For use by FileSystem classes.
     */
    int getPrefixLength() {
        return prefixLength;
    }

    
The system-dependent default name-separator character.  This field is
initialized to contain the first character of the value of the system
property file.separator.  On UNIX systems the value of this
field is '/'; on Microsoft Windows systems it is '\\'.
See Also:
getProperty.getProperty(String)/**
     * The system-dependent default name-separator character.  This field is
     * initialized to contain the first character of the value of the system
     * property <code>file.separator</code>.  On UNIX systems the value of this
     * field is <code>'/'</code>; on Microsoft Windows systems it is <code>'\\'</code>.
     *
     * @see     java.lang.System#getProperty(java.lang.String)
     */
    public static final char separatorChar = fs.getSeparator();

    
The system-dependent default name-separator character, represented as a string for convenience. This string contains a single character, namely separatorChar. /**
     * The system-dependent default name-separator character, represented as a
     * string for convenience.  This string contains a single character, namely
     * {@link #separatorChar}.
     */
    public static final String separator = "" + separatorChar;

    
The system-dependent path-separator character.  This field is
initialized to contain the first character of the value of the system
property path.separator.  This character is used to
separate filenames in a sequence of files given as a path list.
On UNIX systems, this character is ':'; on Microsoft Windows systems it
is ';'.
See Also:
getProperty.getProperty(String)/**
     * The system-dependent path-separator character.  This field is
     * initialized to contain the first character of the value of the system
     * property <code>path.separator</code>.  This character is used to
     * separate filenames in a sequence of files given as a <em>path list</em>.
     * On UNIX systems, this character is <code>':'</code>; on Microsoft Windows systems it
     * is <code>';'</code>.
     *
     * @see     java.lang.System#getProperty(java.lang.String)
     */
    public static final char pathSeparatorChar = fs.getPathSeparator();

    
The system-dependent path-separator character, represented as a string for convenience. This string contains a single character, namely pathSeparatorChar. /**
     * The system-dependent path-separator character, represented as a string
     * for convenience.  This string contains a single character, namely
     * {@link #pathSeparatorChar}.
     */
    public static final String pathSeparator = "" + pathSeparatorChar;


    /* -- Constructors -- */

    
Internal constructor for already-normalized pathname strings.
/**
     * Internal constructor for already-normalized pathname strings.
     */
    private File(String pathname, int prefixLength) {
        this.path = pathname;
        this.prefixLength = prefixLength;
    }

    
Internal constructor for already-normalized pathname strings.
The parameter order is used to disambiguate this method from the
public(File, String) constructor.
/**
     * Internal constructor for already-normalized pathname strings.
     * The parameter order is used to disambiguate this method from the
     * public(File, String) constructor.
     */
    private File(String child, File parent) {
        assert parent.path != null;
        assert (!parent.path.equals(""));
        this.path = fs.resolve(parent.path, child);
        this.prefixLength = parent.prefixLength;
    }

    
Creates a new File instance by converting the given
pathname string into an abstract pathname.  If the given string is
the empty string, then the result is the empty abstract pathname.
Params:
pathname –  A pathname string
Throws:
NullPointerException – 
         If the pathname argument is null/**
     * Creates a new <code>File</code> instance by converting the given
     * pathname string into an abstract pathname.  If the given string is
     * the empty string, then the result is the empty abstract pathname.
     *
     * @param   pathname  A pathname string
     * @throws  NullPointerException
     *          If the <code>pathname</code> argument is <code>null</code>
     */
    public File(String pathname) {
        if (pathname == null) {
            throw new NullPointerException();
        }
        this.path = fs.normalize(pathname);
        this.prefixLength = fs.prefixLength(this.path);
    }

    /* Note: The two-argument File constructors do not interpret an empty
       parent abstract pathname as the current user directory.  An empty parent
       instead causes the child to be resolved against the system-dependent
       directory defined by the FileSystem.getDefaultParent method.  On Unix
       this default is "/", while on Microsoft Windows it is "\\".  This is required for
       compatibility with the original behavior of this class. */

    
Creates a new File instance from a parent pathname string
and a child pathname string.
 If parent is null then the new
File instance is created as if by invoking the
single-argument File constructor on the given
child pathname string.
 Otherwise the parent pathname string is taken to denote
a directory, and the child pathname string is taken to
denote either a directory or a file.  If the child pathname
string is absolute then it is converted into a relative pathname in a
system-dependent way.  If parent is the empty string then
the new File instance is created by converting
child into an abstract pathname and resolving the result
against a system-dependent default directory.  Otherwise each pathname
string is converted into an abstract pathname and the child abstract
pathname is resolved against the parent.
Params:
parent –  The parent pathname string
child –   The child pathname string
Throws:
NullPointerException – 
         If child is null/**
     * Creates a new <code>File</code> instance from a parent pathname string
     * and a child pathname string.
     *
     * <p> If <code>parent</code> is <code>null</code> then the new
     * <code>File</code> instance is created as if by invoking the
     * single-argument <code>File</code> constructor on the given
     * <code>child</code> pathname string.
     *
     * <p> Otherwise the <code>parent</code> pathname string is taken to denote
     * a directory, and the <code>child</code> pathname string is taken to
     * denote either a directory or a file.  If the <code>child</code> pathname
     * string is absolute then it is converted into a relative pathname in a
     * system-dependent way.  If <code>parent</code> is the empty string then
     * the new <code>File</code> instance is created by converting
     * <code>child</code> into an abstract pathname and resolving the result
     * against a system-dependent default directory.  Otherwise each pathname
     * string is converted into an abstract pathname and the child abstract
     * pathname is resolved against the parent.
     *
     * @param   parent  The parent pathname string
     * @param   child   The child pathname string
     * @throws  NullPointerException
     *          If <code>child</code> is <code>null</code>
     */
    public File(String parent, String child) {
        if (child == null) {
            throw new NullPointerException();
        }
        if (parent != null) {
            if (parent.equals("")) {
                this.path = fs.resolve(fs.getDefaultParent(),
                                       fs.normalize(child));
            } else {
                this.path = fs.resolve(fs.normalize(parent),
                                       fs.normalize(child));
            }
        } else {
            this.path = fs.normalize(child);
        }
        this.prefixLength = fs.prefixLength(this.path);
    }

    
Creates a new File instance from a parent abstract
pathname and a child pathname string.
 If parent is null then the new
File instance is created as if by invoking the
single-argument File constructor on the given
child pathname string.
 Otherwise the parent abstract pathname is taken to
denote a directory, and the child pathname string is taken
to denote either a directory or a file.  If the child
pathname string is absolute then it is converted into a relative
pathname in a system-dependent way.  If parent is the empty
abstract pathname then the new File instance is created by
converting child into an abstract pathname and resolving
the result against a system-dependent default directory.  Otherwise each
pathname string is converted into an abstract pathname and the child
abstract pathname is resolved against the parent.
Params:
parent –  The parent abstract pathname
child –   The child pathname string
Throws:
NullPointerException – 
         If child is null/**
     * Creates a new <code>File</code> instance from a parent abstract
     * pathname and a child pathname string.
     *
     * <p> If <code>parent</code> is <code>null</code> then the new
     * <code>File</code> instance is created as if by invoking the
     * single-argument <code>File</code> constructor on the given
     * <code>child</code> pathname string.
     *
     * <p> Otherwise the <code>parent</code> abstract pathname is taken to
     * denote a directory, and the <code>child</code> pathname string is taken
     * to denote either a directory or a file.  If the <code>child</code>
     * pathname string is absolute then it is converted into a relative
     * pathname in a system-dependent way.  If <code>parent</code> is the empty
     * abstract pathname then the new <code>File</code> instance is created by
     * converting <code>child</code> into an abstract pathname and resolving
     * the result against a system-dependent default directory.  Otherwise each
     * pathname string is converted into an abstract pathname and the child
     * abstract pathname is resolved against the parent.
     *
     * @param   parent  The parent abstract pathname
     * @param   child   The child pathname string
     * @throws  NullPointerException
     *          If <code>child</code> is <code>null</code>
     */
    public File(File parent, String child) {
        if (child == null) {
            throw new NullPointerException();
        }
        if (parent != null) {
            if (parent.path.equals("")) {
                this.path = fs.resolve(fs.getDefaultParent(),
                                       fs.normalize(child));
            } else {
                this.path = fs.resolve(parent.path,
                                       fs.normalize(child));
            }
        } else {
            this.path = fs.normalize(child);
        }
        this.prefixLength = fs.prefixLength(this.path);
    }

    
Creates a new File instance by converting the given file: URI into an abstract pathname. 
 The exact form of a file: URI is system-dependent, hence the transformation performed by this constructor is also system-dependent. 
 For a given abstract pathname f it is guaranteed that

new File( f.
toURI()).equals( f.getAbsoluteFile()) 
 so long as the original abstract pathname, the URI, and the new abstract pathname are all created in (possibly different invocations of) the same Java virtual machine. This relationship typically does not hold, however, when a file: URI that is created in a virtual machine on one operating system is converted into an abstract pathname in a virtual machine on a different operating system. 
Params:
uri –  An absolute, hierarchical URI with a scheme equal to "file", a non-empty path component, and undefined authority, query, and fragment components
Throws:
NullPointerException –  If uri is null
IllegalArgumentException – 
         If the preconditions on the parameter do not hold
See Also:
toURI()
URI
Since:
1.4/**
     * Creates a new {@code File} instance by converting the given
     * {@code file:} URI into an abstract pathname.
     *
     * <p> The exact form of a {@code file:} URI is system-dependent, hence
     * the transformation performed by this constructor is also
     * system-dependent.
     *
     * <p> For a given abstract pathname <i>f</i> it is guaranteed that
     *
     * <blockquote><code>
     * new File(</code><i>&nbsp;f</i><code>.{@link #toURI()
     * toURI}()).equals(</code><i>&nbsp;f</i><code>.{@link #getAbsoluteFile() getAbsoluteFile}())
     * </code></blockquote>
     *
     * so long as the original abstract pathname, the URI, and the new abstract
     * pathname are all created in (possibly different invocations of) the same
     * Java virtual machine.  This relationship typically does not hold,
     * however, when a {@code file:} URI that is created in a virtual machine
     * on one operating system is converted into an abstract pathname in a
     * virtual machine on a different operating system.
     *
     * @param  uri
     *         An absolute, hierarchical URI with a scheme equal to
     *         {@code "file"}, a non-empty path component, and undefined
     *         authority, query, and fragment components
     *
     * @throws  NullPointerException
     *          If {@code uri} is {@code null}
     *
     * @throws  IllegalArgumentException
     *          If the preconditions on the parameter do not hold
     *
     * @see #toURI()
     * @see java.net.URI
     * @since 1.4
     */
    public File(URI uri) {

        // Check our many preconditions
        if (!uri.isAbsolute())
            throw new IllegalArgumentException("URI is not absolute");
        if (uri.isOpaque())
            throw new IllegalArgumentException("URI is not hierarchical");
        String scheme = uri.getScheme();
        if ((scheme == null) || !scheme.equalsIgnoreCase("file"))
            throw new IllegalArgumentException("URI scheme is not \"file\"");
        if (uri.getRawAuthority() != null)
            throw new IllegalArgumentException("URI has an authority component");
        if (uri.getRawFragment() != null)
            throw new IllegalArgumentException("URI has a fragment component");
        if (uri.getRawQuery() != null)
            throw new IllegalArgumentException("URI has a query component");
        String p = uri.getPath();
        if (p.equals(""))
            throw new IllegalArgumentException("URI path component is empty");

        // Okay, now initialize
        p = fs.fromURIPath(p);
        if (File.separatorChar != '/')
            p = p.replace('/', File.separatorChar);
        this.path = fs.normalize(p);
        this.prefixLength = fs.prefixLength(this.path);
    }


    /* -- Path-component accessors -- */

    
Returns the name of the file or directory denoted by this abstract
pathname.  This is just the last name in the pathname's name
sequence.  If the pathname's name sequence is empty, then the empty
string is returned.
Returns:
 The name of the file or directory denoted by this abstract
         pathname, or the empty string if this pathname's name sequence
         is empty/**
     * Returns the name of the file or directory denoted by this abstract
     * pathname.  This is just the last name in the pathname's name
     * sequence.  If the pathname's name sequence is empty, then the empty
     * string is returned.
     *
     * @return  The name of the file or directory denoted by this abstract
     *          pathname, or the empty string if this pathname's name sequence
     *          is empty
     */
    public String getName() {
        int index = path.lastIndexOf(separatorChar);
        if (index < prefixLength) return path.substring(prefixLength);
        return path.substring(index + 1);
    }

    
Returns the pathname string of this abstract pathname's parent, or
null if this pathname does not name a parent directory.
 The parent of an abstract pathname consists of the
pathname's prefix, if any, and each name in the pathname's name
sequence except for the last.  If the name sequence is empty then
the pathname does not name a parent directory.
Returns:
 The pathname string of the parent directory named by this
         abstract pathname, or null if this pathname
         does not name a parent/**
     * Returns the pathname string of this abstract pathname's parent, or
     * <code>null</code> if this pathname does not name a parent directory.
     *
     * <p> The <em>parent</em> of an abstract pathname consists of the
     * pathname's prefix, if any, and each name in the pathname's name
     * sequence except for the last.  If the name sequence is empty then
     * the pathname does not name a parent directory.
     *
     * @return  The pathname string of the parent directory named by this
     *          abstract pathname, or <code>null</code> if this pathname
     *          does not name a parent
     */
    public String getParent() {
        int index = path.lastIndexOf(separatorChar);
        if (index < prefixLength) {
            if ((prefixLength > 0) && (path.length() > prefixLength))
                return path.substring(0, prefixLength);
            return null;
        }
        return path.substring(0, index);
    }

    
Returns the abstract pathname of this abstract pathname's parent,
or null if this pathname does not name a parent
directory.
 The parent of an abstract pathname consists of the
pathname's prefix, if any, and each name in the pathname's name
sequence except for the last.  If the name sequence is empty then
the pathname does not name a parent directory.
Returns:
 The abstract pathname of the parent directory named by this
         abstract pathname, or null if this pathname
         does not name a parent
Since:
1.2/**
     * Returns the abstract pathname of this abstract pathname's parent,
     * or <code>null</code> if this pathname does not name a parent
     * directory.
     *
     * <p> The <em>parent</em> of an abstract pathname consists of the
     * pathname's prefix, if any, and each name in the pathname's name
     * sequence except for the last.  If the name sequence is empty then
     * the pathname does not name a parent directory.
     *
     * @return  The abstract pathname of the parent directory named by this
     *          abstract pathname, or <code>null</code> if this pathname
     *          does not name a parent
     *
     * @since 1.2
     */
    public File getParentFile() {
        String p = this.getParent();
        if (p == null) return null;
        return new File(p, this.prefixLength);
    }

    
Converts this abstract pathname into a pathname string. The resulting string uses the default name-separator character to separate the names in the name sequence. 
Returns:
 The string form of this abstract pathname/**
     * Converts this abstract pathname into a pathname string.  The resulting
     * string uses the {@link #separator default name-separator character} to
     * separate the names in the name sequence.
     *
     * @return  The string form of this abstract pathname
     */
    public String getPath() {
        return path;
    }


    /* -- Path operations -- */

    
Tests whether this abstract pathname is absolute.  The definition of
absolute pathname is system dependent.  On UNIX systems, a pathname is
absolute if its prefix is "/".  On Microsoft Windows systems, a
pathname is absolute if its prefix is a drive specifier followed by
"\\", or if its prefix is "\\\\".
Returns:
 true if this abstract pathname is absolute,
         false otherwise/**
     * Tests whether this abstract pathname is absolute.  The definition of
     * absolute pathname is system dependent.  On UNIX systems, a pathname is
     * absolute if its prefix is <code>"/"</code>.  On Microsoft Windows systems, a
     * pathname is absolute if its prefix is a drive specifier followed by
     * <code>"\\"</code>, or if its prefix is <code>"\\\\"</code>.
     *
     * @return  <code>true</code> if this abstract pathname is absolute,
     *          <code>false</code> otherwise
     */
    public boolean isAbsolute() {
        return fs.isAbsolute(this);
    }

    
Returns the absolute pathname string of this abstract pathname.
 If this abstract pathname is already absolute, then the pathname string is simply returned as if by the getPath method. If this abstract pathname is the empty abstract pathname then the pathname string of the current user directory, which is named by the system property user.dir, is returned.  Otherwise this
pathname is resolved in a system-dependent way.  On UNIX systems, a
relative pathname is made absolute by resolving it against the current
user directory.  On Microsoft Windows systems, a relative pathname is made absolute
by resolving it against the current directory of the drive named by the
pathname, if any; if not, it is resolved against the current user
directory.
Throws:
SecurityException – 
         If a required system property value cannot be accessed.
See Also:
isAbsolute()
Returns:
 The absolute pathname string denoting the same file or
         directory as this abstract pathname/**
     * Returns the absolute pathname string of this abstract pathname.
     *
     * <p> If this abstract pathname is already absolute, then the pathname
     * string is simply returned as if by the {@link #getPath}
     * method.  If this abstract pathname is the empty abstract pathname then
     * the pathname string of the current user directory, which is named by the
     * system property <code>user.dir</code>, is returned.  Otherwise this
     * pathname is resolved in a system-dependent way.  On UNIX systems, a
     * relative pathname is made absolute by resolving it against the current
     * user directory.  On Microsoft Windows systems, a relative pathname is made absolute
     * by resolving it against the current directory of the drive named by the
     * pathname, if any; if not, it is resolved against the current user
     * directory.
     *
     * @return  The absolute pathname string denoting the same file or
     *          directory as this abstract pathname
     *
     * @throws  SecurityException
     *          If a required system property value cannot be accessed.
     *
     * @see     java.io.File#isAbsolute()
     */
    public String getAbsolutePath() {
        return fs.resolve(this);
    }

    
Returns the absolute form of this abstract pathname.  Equivalent to
new File(this.getAbsolutePath).
Throws:
SecurityException – 
         If a required system property value cannot be accessed.
Returns:
 The absolute abstract pathname denoting the same file or
         directory as this abstract pathname
Since:
1.2/**
     * Returns the absolute form of this abstract pathname.  Equivalent to
     * <code>new&nbsp;File(this.{@link #getAbsolutePath})</code>.
     *
     * @return  The absolute abstract pathname denoting the same file or
     *          directory as this abstract pathname
     *
     * @throws  SecurityException
     *          If a required system property value cannot be accessed.
     *
     * @since 1.2
     */
    public File getAbsoluteFile() {
        String absPath = getAbsolutePath();
        return new File(absPath, fs.prefixLength(absPath));
    }

    
Returns the canonical pathname string of this abstract pathname.
 A canonical pathname is both absolute and unique. The precise definition of canonical form is system-dependent. This method first converts this pathname to absolute form if necessary, as if by invoking the getAbsolutePath method, and then maps it to its unique form in a system-dependent way. This typically involves removing redundant names such as "." and ".." from the pathname, resolving symbolic links (on UNIX platforms), and converting drive letters to a standard case (on Microsoft Windows platforms). 
 Every pathname that denotes an existing file or directory has a
unique canonical form.  Every pathname that denotes a nonexistent file
or directory also has a unique canonical form.  The canonical form of
the pathname of a nonexistent file or directory may be different from
the canonical form of the same pathname after the file or directory is
created.  Similarly, the canonical form of the pathname of an existing
file or directory may be different from the canonical form of the same
pathname after the file or directory is deleted.
Throws:
IOException – 
         If an I/O error occurs, which is possible because the
         construction of the canonical pathname may require
         filesystem queries
SecurityException –  If a required system property value cannot be accessed, or if a security manager exists and its SecurityManager.checkRead method denies read access to the file
See Also:
Path.toRealPath
Returns:
 The canonical pathname string denoting the same file or
         directory as this abstract pathname
Since:
  1.1/**
     * Returns the canonical pathname string of this abstract pathname.
     *
     * <p> A canonical pathname is both absolute and unique.  The precise
     * definition of canonical form is system-dependent.  This method first
     * converts this pathname to absolute form if necessary, as if by invoking the
     * {@link #getAbsolutePath} method, and then maps it to its unique form in a
     * system-dependent way.  This typically involves removing redundant names
     * such as {@code "."} and {@code ".."} from the pathname, resolving
     * symbolic links (on UNIX platforms), and converting drive letters to a
     * standard case (on Microsoft Windows platforms).
     *
     * <p> Every pathname that denotes an existing file or directory has a
     * unique canonical form.  Every pathname that denotes a nonexistent file
     * or directory also has a unique canonical form.  The canonical form of
     * the pathname of a nonexistent file or directory may be different from
     * the canonical form of the same pathname after the file or directory is
     * created.  Similarly, the canonical form of the pathname of an existing
     * file or directory may be different from the canonical form of the same
     * pathname after the file or directory is deleted.
     *
     * @return  The canonical pathname string denoting the same file or
     *          directory as this abstract pathname
     *
     * @throws  IOException
     *          If an I/O error occurs, which is possible because the
     *          construction of the canonical pathname may require
     *          filesystem queries
     *
     * @throws  SecurityException
     *          If a required system property value cannot be accessed, or
     *          if a security manager exists and its {@link
     *          java.lang.SecurityManager#checkRead} method denies
     *          read access to the file
     *
     * @since   1.1
     * @see     Path#toRealPath
     */
    public String getCanonicalPath() throws IOException {
        if (isInvalid()) {
            throw new IOException("Invalid file path");
        }
        return fs.canonicalize(fs.resolve(this));
    }

    
Returns the canonical form of this abstract pathname.  Equivalent to
new File(this.getCanonicalPath).
Throws:
IOException – 
         If an I/O error occurs, which is possible because the
         construction of the canonical pathname may require
         filesystem queries
SecurityException –  If a required system property value cannot be accessed, or if a security manager exists and its SecurityManager.checkRead method denies read access to the file
See Also:
Path.toRealPath
Returns:
 The canonical pathname string denoting the same file or
         directory as this abstract pathname
Since:
1.2/**
     * Returns the canonical form of this abstract pathname.  Equivalent to
     * <code>new&nbsp;File(this.{@link #getCanonicalPath})</code>.
     *
     * @return  The canonical pathname string denoting the same file or
     *          directory as this abstract pathname
     *
     * @throws  IOException
     *          If an I/O error occurs, which is possible because the
     *          construction of the canonical pathname may require
     *          filesystem queries
     *
     * @throws  SecurityException
     *          If a required system property value cannot be accessed, or
     *          if a security manager exists and its {@link
     *          java.lang.SecurityManager#checkRead} method denies
     *          read access to the file
     *
     * @since 1.2
     * @see     Path#toRealPath
     */
    public File getCanonicalFile() throws IOException {
        String canonPath = getCanonicalPath();
        return new File(canonPath, fs.prefixLength(canonPath));
    }

    private static String slashify(String path, boolean isDirectory) {
        String p = path;
        if (File.separatorChar != '/')
            p = p.replace(File.separatorChar, '/');
        if (!p.startsWith("/"))
            p = "/" + p;
        if (!p.endsWith("/") && isDirectory)
            p = p + "/";
        return p;
    }

    
Converts this abstract pathname into a file: URL.  The
exact form of the URL is system-dependent.  If it can be determined that
the file denoted by this abstract pathname is a directory, then the
resulting URL will end with a slash.
Throws:
MalformedURLException – 
         If the path cannot be parsed as a URL
See Also:
toURI()
URI
URI.toURL()
URL
Returns:
 A URL object representing the equivalent file URL
Since:
  1.2
Deprecated:
This method does not automatically escape characters that are illegal in URLs. It is recommended that new code convert an abstract pathname into a URL by first converting it into a URI, via the toURI method, and then converting the URI into a URL via the URI.toURL method./**
     * Converts this abstract pathname into a <code>file:</code> URL.  The
     * exact form of the URL is system-dependent.  If it can be determined that
     * the file denoted by this abstract pathname is a directory, then the
     * resulting URL will end with a slash.
     *
     * @return  A URL object representing the equivalent file URL
     *
     * @throws  MalformedURLException
     *          If the path cannot be parsed as a URL
     *
     * @see     #toURI()
     * @see     java.net.URI
     * @see     java.net.URI#toURL()
     * @see     java.net.URL
     * @since   1.2
     *
     * @deprecated This method does not automatically escape characters that
     * are illegal in URLs.  It is recommended that new code convert an
     * abstract pathname into a URL by first converting it into a URI, via the
     * {@link #toURI() toURI} method, and then converting the URI into a URL
     * via the {@link java.net.URI#toURL() URI.toURL} method.
     */
    @Deprecated
    public URL toURL() throws MalformedURLException {
        if (isInvalid()) {
            throw new MalformedURLException("Invalid file path");
        }
        return new URL("file", "", slashify(getAbsolutePath(), isDirectory()));
    }

    
Constructs a file: URI that represents this abstract pathname. 
 The exact form of the URI is system-dependent.  If it can be
determined that the file denoted by this abstract pathname is a
directory, then the resulting URI will end with a slash.
 For a given abstract pathname f, it is guaranteed that
 new File( f.toURI()).equals(
 f.getAbsoluteFile()) 
 so long as the original abstract pathname, the URI, and the new abstract pathname are all created in (possibly different invocations of) the same Java virtual machine. Due to the system-dependent nature of abstract pathnames, however, this relationship typically does not hold when a file: URI that is created in a virtual machine on one operating system is converted into an abstract pathname in a virtual machine on a different operating system. 
 Note that when this abstract pathname represents a UNC pathname then all components of the UNC (including the server name component) are encoded in the URI path. The authority component is undefined, meaning that it is represented as null. The Path class defines the toUri method to encode the server name in the authority component of the resulting URI. The toPath method may be used to obtain a Path representing this abstract pathname. 
Throws:
SecurityException – If a required system property value cannot
be accessed.
See Also:
File(URI)
URI
URI.toURL()
Returns:
 An absolute, hierarchical URI with a scheme equal to "file", a path representing this abstract pathname, and undefined authority, query, and fragment components
Since:
1.4/**
     * Constructs a {@code file:} URI that represents this abstract pathname.
     *
     * <p> The exact form of the URI is system-dependent.  If it can be
     * determined that the file denoted by this abstract pathname is a
     * directory, then the resulting URI will end with a slash.
     *
     * <p> For a given abstract pathname <i>f</i>, it is guaranteed that
     *
     * <blockquote><code>
     * new {@link #File(java.net.URI) File}(</code><i>&nbsp;f</i><code>.toURI()).equals(
     * </code><i>&nbsp;f</i><code>.{@link #getAbsoluteFile() getAbsoluteFile}())
     * </code></blockquote>
     *
     * so long as the original abstract pathname, the URI, and the new abstract
     * pathname are all created in (possibly different invocations of) the same
     * Java virtual machine.  Due to the system-dependent nature of abstract
     * pathnames, however, this relationship typically does not hold when a
     * {@code file:} URI that is created in a virtual machine on one operating
     * system is converted into an abstract pathname in a virtual machine on a
     * different operating system.
     *
     * <p> Note that when this abstract pathname represents a UNC pathname then
     * all components of the UNC (including the server name component) are encoded
     * in the {@code URI} path. The authority component is undefined, meaning
     * that it is represented as {@code null}. The {@link Path} class defines the
     * {@link Path#toUri toUri} method to encode the server name in the authority
     * component of the resulting {@code URI}. The {@link #toPath toPath} method
     * may be used to obtain a {@code Path} representing this abstract pathname.
     *
     * @return  An absolute, hierarchical URI with a scheme equal to
     *          {@code "file"}, a path representing this abstract pathname,
     *          and undefined authority, query, and fragment components
     * @throws SecurityException If a required system property value cannot
     * be accessed.
     *
     * @see #File(java.net.URI)
     * @see java.net.URI
     * @see java.net.URI#toURL()
     * @since 1.4
     */
    public URI toURI() {
        try {
            File f = getAbsoluteFile();
            String sp = slashify(f.getPath(), f.isDirectory());
            if (sp.startsWith("//"))
                sp = "//" + sp;
            return new URI("file", null, sp, null);
        } catch (URISyntaxException x) {
            throw new Error(x);         // Can't happen
        }
    }


    /* -- Attribute accessors -- */

    
Tests whether the application can read the file denoted by this abstract pathname. On some platforms it may be possible to start the Java virtual machine with special privileges that allow it to read files that are marked as unreadable. Consequently this method may return true even though the file does not have read permissions. 
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkRead(String) method denies read access to the file
Returns:
 true if and only if the file specified by this
         abstract pathname exists and can be read by the
         application; false otherwise/**
     * Tests whether the application can read the file denoted by this
     * abstract pathname. On some platforms it may be possible to start the
     * Java virtual machine with special privileges that allow it to read
     * files that are marked as unreadable. Consequently this method may return
     * {@code true} even though the file does not have read permissions.
     *
     * @return  <code>true</code> if and only if the file specified by this
     *          abstract pathname exists <em>and</em> can be read by the
     *          application; <code>false</code> otherwise
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkRead(java.lang.String)}
     *          method denies read access to the file
     */
    public boolean canRead() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkRead(path);
        }
        if (isInvalid()) {
            return false;
        }
        return fs.checkAccess(this, FileSystem.ACCESS_READ);
    }

    
Tests whether the application can modify the file denoted by this abstract pathname. On some platforms it may be possible to start the Java virtual machine with special privileges that allow it to modify files that are marked read-only. Consequently this method may return true even though the file is marked read-only. 
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkWrite(String) method denies write access to the file
Returns:
 true if and only if the file system actually
         contains a file denoted by this abstract pathname and
         the application is allowed to write to the file;
         false otherwise./**
     * Tests whether the application can modify the file denoted by this
     * abstract pathname. On some platforms it may be possible to start the
     * Java virtual machine with special privileges that allow it to modify
     * files that are marked read-only. Consequently this method may return
     * {@code true} even though the file is marked read-only.
     *
     * @return  <code>true</code> if and only if the file system actually
     *          contains a file denoted by this abstract pathname <em>and</em>
     *          the application is allowed to write to the file;
     *          <code>false</code> otherwise.
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkWrite(java.lang.String)}
     *          method denies write access to the file
     */
    public boolean canWrite() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkWrite(path);
        }
        if (isInvalid()) {
            return false;
        }
        return fs.checkAccess(this, FileSystem.ACCESS_WRITE);
    }

    
Tests whether the file or directory denoted by this abstract pathname
exists.
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkRead(String) method denies read access to the file or directory
Returns:
 true if and only if the file or directory denoted
         by this abstract pathname exists; false otherwise/**
     * Tests whether the file or directory denoted by this abstract pathname
     * exists.
     *
     * @return  <code>true</code> if and only if the file or directory denoted
     *          by this abstract pathname exists; <code>false</code> otherwise
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkRead(java.lang.String)}
     *          method denies read access to the file or directory
     */
    public boolean exists() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkRead(path);
        }
        if (isInvalid()) {
            return false;
        }
        return ((fs.getBooleanAttributes(this) & FileSystem.BA_EXISTS) != 0);
    }

    
Tests whether the file denoted by this abstract pathname is a
directory.
 Where it is required to distinguish an I/O exception from the case that the file is not a directory, or where several attributes of the same file are required at the same time, then the 
Files.readAttributes method may be used. 
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkRead(String) method denies read access to the file
Returns:
true if and only if the file denoted by this
         abstract pathname exists and is a directory;
         false otherwise/**
     * Tests whether the file denoted by this abstract pathname is a
     * directory.
     *
     * <p> Where it is required to distinguish an I/O exception from the case
     * that the file is not a directory, or where several attributes of the
     * same file are required at the same time, then the {@link
     * java.nio.file.Files#readAttributes(Path,Class,LinkOption[])
     * Files.readAttributes} method may be used.
     *
     * @return <code>true</code> if and only if the file denoted by this
     *          abstract pathname exists <em>and</em> is a directory;
     *          <code>false</code> otherwise
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkRead(java.lang.String)}
     *          method denies read access to the file
     */
    public boolean isDirectory() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkRead(path);
        }
        if (isInvalid()) {
            return false;
        }
        return ((fs.getBooleanAttributes(this) & FileSystem.BA_DIRECTORY)
                != 0);
    }

    
Tests whether the file denoted by this abstract pathname is a normal
file.  A file is normal if it is not a directory and, in
addition, satisfies other system-dependent criteria.  Any non-directory
file created by a Java application is guaranteed to be a normal file.
 Where it is required to distinguish an I/O exception from the case that the file is not a normal file, or where several attributes of the same file are required at the same time, then the 
Files.readAttributes method may be used. 
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkRead(String) method denies read access to the file
Returns:
 true if and only if the file denoted by this
         abstract pathname exists and is a normal file;
         false otherwise/**
     * Tests whether the file denoted by this abstract pathname is a normal
     * file.  A file is <em>normal</em> if it is not a directory and, in
     * addition, satisfies other system-dependent criteria.  Any non-directory
     * file created by a Java application is guaranteed to be a normal file.
     *
     * <p> Where it is required to distinguish an I/O exception from the case
     * that the file is not a normal file, or where several attributes of the
     * same file are required at the same time, then the {@link
     * java.nio.file.Files#readAttributes(Path,Class,LinkOption[])
     * Files.readAttributes} method may be used.
     *
     * @return  <code>true</code> if and only if the file denoted by this
     *          abstract pathname exists <em>and</em> is a normal file;
     *          <code>false</code> otherwise
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkRead(java.lang.String)}
     *          method denies read access to the file
     */
    public boolean isFile() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkRead(path);
        }
        if (isInvalid()) {
            return false;
        }
        return ((fs.getBooleanAttributes(this) & FileSystem.BA_REGULAR) != 0);
    }

    
Tests whether the file named by this abstract pathname is a hidden
file.  The exact definition of hidden is system-dependent.  On
UNIX systems, a file is considered to be hidden if its name begins with
a period character ('.').  On Microsoft Windows systems, a file is
considered to be hidden if it has been marked as such in the filesystem.
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkRead(String) method denies read access to the file
Returns:
 true if and only if the file denoted by this
         abstract pathname is hidden according to the conventions of the
         underlying platform
Since:
1.2/**
     * Tests whether the file named by this abstract pathname is a hidden
     * file.  The exact definition of <em>hidden</em> is system-dependent.  On
     * UNIX systems, a file is considered to be hidden if its name begins with
     * a period character (<code>'.'</code>).  On Microsoft Windows systems, a file is
     * considered to be hidden if it has been marked as such in the filesystem.
     *
     * @return  <code>true</code> if and only if the file denoted by this
     *          abstract pathname is hidden according to the conventions of the
     *          underlying platform
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkRead(java.lang.String)}
     *          method denies read access to the file
     *
     * @since 1.2
     */
    public boolean isHidden() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkRead(path);
        }
        if (isInvalid()) {
            return false;
        }
        return ((fs.getBooleanAttributes(this) & FileSystem.BA_HIDDEN) != 0);
    }

    
Returns the time that the file denoted by this abstract pathname was
last modified.
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkRead(String) method denies read access to the file
API Note:

While the unit of time of the return value is milliseconds, the
granularity of the value depends on the underlying file system and may
be larger.  For example, some file systems use time stamps in units of
seconds.
 Where it is required to distinguish an I/O exception from the case where 0L is returned, or where several attributes of the same file are required at the same time, or where the time of last access or the creation time are required, then the 
Files.readAttributes method may be used. If however only the time of last modification is required, then the 
Files.getLastModifiedTime method may be used instead.
Returns:
 A long value representing the time the file was
         last modified, measured in milliseconds since the epoch
         (00:00:00 GMT, January 1, 1970), or 0L if the
         file does not exist or if an I/O error occurs.  The value may
         be negative indicating the number of milliseconds before the
         epoch/**
     * Returns the time that the file denoted by this abstract pathname was
     * last modified.
     *
     * @apiNote
     * While the unit of time of the return value is milliseconds, the
     * granularity of the value depends on the underlying file system and may
     * be larger.  For example, some file systems use time stamps in units of
     * seconds.
     *
     * <p> Where it is required to distinguish an I/O exception from the case
     * where {@code 0L} is returned, or where several attributes of the
     * same file are required at the same time, or where the time of last
     * access or the creation time are required, then the {@link
     * java.nio.file.Files#readAttributes(Path,Class,LinkOption[])
     * Files.readAttributes} method may be used.  If however only the
     * time of last modification is required, then the
     * {@link java.nio.file.Files#getLastModifiedTime(Path,LinkOption[])
     * Files.getLastModifiedTime} method may be used instead.
     *
     * @return  A <code>long</code> value representing the time the file was
     *          last modified, measured in milliseconds since the epoch
     *          (00:00:00 GMT, January 1, 1970), or <code>0L</code> if the
     *          file does not exist or if an I/O error occurs.  The value may
     *          be negative indicating the number of milliseconds before the
     *          epoch
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkRead(java.lang.String)}
     *          method denies read access to the file
     */
    public long lastModified() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkRead(path);
        }
        if (isInvalid()) {
            return 0L;
        }
        return fs.getLastModifiedTime(this);
    }

    
Returns the length of the file denoted by this abstract pathname.
The return value is unspecified if this pathname denotes a directory.
 Where it is required to distinguish an I/O exception from the case that 0L is returned, or where several attributes of the same file are required at the same time, then the 
Files.readAttributes method may be used. 
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkRead(String) method denies read access to the file
Returns:
 The length, in bytes, of the file denoted by this abstract
         pathname, or 0L if the file does not exist.  Some
         operating systems may return 0L for pathnames
         denoting system-dependent entities such as devices or pipes./**
     * Returns the length of the file denoted by this abstract pathname.
     * The return value is unspecified if this pathname denotes a directory.
     *
     * <p> Where it is required to distinguish an I/O exception from the case
     * that {@code 0L} is returned, or where several attributes of the same file
     * are required at the same time, then the {@link
     * java.nio.file.Files#readAttributes(Path,Class,LinkOption[])
     * Files.readAttributes} method may be used.
     *
     * @return  The length, in bytes, of the file denoted by this abstract
     *          pathname, or <code>0L</code> if the file does not exist.  Some
     *          operating systems may return <code>0L</code> for pathnames
     *          denoting system-dependent entities such as devices or pipes.
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkRead(java.lang.String)}
     *          method denies read access to the file
     */
    public long length() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkRead(path);
        }
        if (isInvalid()) {
            return 0L;
        }
        return fs.getLength(this);
    }


    /* -- File operations -- */

    
Atomically creates a new, empty file named by this abstract pathname if
and only if a file with this name does not yet exist.  The check for the
existence of the file and the creation of the file if it does not exist
are a single operation that is atomic with respect to all other
filesystem activities that might affect the file.

Note: this method should not be used for file-locking, as the resulting protocol cannot be made to work reliably. The FileLock facility should be used instead. 
Throws:
IOException – 
         If an I/O error occurred
SecurityException –  If a security manager exists and its SecurityManager.checkWrite(String) method denies write access to the file
Returns:
 true if the named file does not exist and was
         successfully created; false if the named file
         already exists
Since:
1.2/**
     * Atomically creates a new, empty file named by this abstract pathname if
     * and only if a file with this name does not yet exist.  The check for the
     * existence of the file and the creation of the file if it does not exist
     * are a single operation that is atomic with respect to all other
     * filesystem activities that might affect the file.
     * <P>
     * Note: this method should <i>not</i> be used for file-locking, as
     * the resulting protocol cannot be made to work reliably. The
     * {@link java.nio.channels.FileLock FileLock}
     * facility should be used instead.
     *
     * @return  <code>true</code> if the named file does not exist and was
     *          successfully created; <code>false</code> if the named file
     *          already exists
     *
     * @throws  IOException
     *          If an I/O error occurred
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkWrite(java.lang.String)}
     *          method denies write access to the file
     *
     * @since 1.2
     */
    public boolean createNewFile() throws IOException {
        SecurityManager security = System.getSecurityManager();
        if (security != null) security.checkWrite(path);
        if (isInvalid()) {
            throw new IOException("Invalid file path");
        }
        return fs.createFileExclusively(path);
    }

    
Deletes the file or directory denoted by this abstract pathname.  If
this pathname denotes a directory, then the directory must be empty in
order to be deleted.
 Note that the Files class defines the delete method to throw an IOException when a file cannot be deleted. This is useful for error reporting and to diagnose why a file cannot be deleted. 
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkDelete method denies delete access to the file
Returns:
 true if and only if the file or directory is
         successfully deleted; false otherwise/**
     * Deletes the file or directory denoted by this abstract pathname.  If
     * this pathname denotes a directory, then the directory must be empty in
     * order to be deleted.
     *
     * <p> Note that the {@link java.nio.file.Files} class defines the {@link
     * java.nio.file.Files#delete(Path) delete} method to throw an {@link IOException}
     * when a file cannot be deleted. This is useful for error reporting and to
     * diagnose why a file cannot be deleted.
     *
     * @return  <code>true</code> if and only if the file or directory is
     *          successfully deleted; <code>false</code> otherwise
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkDelete} method denies
     *          delete access to the file
     */
    public boolean delete() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkDelete(path);
        }
        if (isInvalid()) {
            return false;
        }
        return fs.delete(this);
    }

    
Requests that the file or directory denoted by this abstract
pathname be deleted when the virtual machine terminates.
Files (or directories) are deleted in the reverse order that
they are registered. Invoking this method to delete a file or
directory that is already registered for deletion has no effect.
Deletion will be attempted only for normal termination of the
virtual machine, as defined by the Java Language Specification.
 Once deletion has been requested, it is not possible to cancel the
request.  This method should therefore be used with care.

Note: this method should not be used for file-locking, as the resulting protocol cannot be made to work reliably. The FileLock facility should be used instead. 
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkDelete method denies delete access to the file
See Also:
delete
Since:
1.2/**
     * Requests that the file or directory denoted by this abstract
     * pathname be deleted when the virtual machine terminates.
     * Files (or directories) are deleted in the reverse order that
     * they are registered. Invoking this method to delete a file or
     * directory that is already registered for deletion has no effect.
     * Deletion will be attempted only for normal termination of the
     * virtual machine, as defined by the Java Language Specification.
     *
     * <p> Once deletion has been requested, it is not possible to cancel the
     * request.  This method should therefore be used with care.
     *
     * <P>
     * Note: this method should <i>not</i> be used for file-locking, as
     * the resulting protocol cannot be made to work reliably. The
     * {@link java.nio.channels.FileLock FileLock}
     * facility should be used instead.
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkDelete} method denies
     *          delete access to the file
     *
     * @see #delete
     *
     * @since 1.2
     */
    public void deleteOnExit() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkDelete(path);
        }
        if (isInvalid()) {
            return;
        }
        DeleteOnExitHook.add(path);
    }

    
Returns an array of strings naming the files and directories in the
directory denoted by this abstract pathname.
 If this abstract pathname does not denote a directory, then this method returns null. Otherwise an array of strings is returned, one for each file or directory in the directory. Names denoting the directory itself and the directory's parent directory are not included in the result. Each string is a file name rather than a complete path. 
 There is no guarantee that the name strings in the resulting array
will appear in any specific order; they are not, in particular,
guaranteed to appear in alphabetical order.
 Note that the Files class defines the newDirectoryStream method to open a directory and iterate over the names of the files in the directory. This may use less resources when working with very large directories, and may be more responsive when working with remote directories. 
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkRead(String) method denies read access to the directory
Returns:
 An array of strings naming the files and directories in the directory denoted by this abstract pathname. The array will be empty if the directory is empty. Returns null if this abstract pathname does not denote a directory, or if an I/O error occurs./**
     * Returns an array of strings naming the files and directories in the
     * directory denoted by this abstract pathname.
     *
     * <p> If this abstract pathname does not denote a directory, then this
     * method returns {@code null}.  Otherwise an array of strings is
     * returned, one for each file or directory in the directory.  Names
     * denoting the directory itself and the directory's parent directory are
     * not included in the result.  Each string is a file name rather than a
     * complete path.
     *
     * <p> There is no guarantee that the name strings in the resulting array
     * will appear in any specific order; they are not, in particular,
     * guaranteed to appear in alphabetical order.
     *
     * <p> Note that the {@link java.nio.file.Files} class defines the {@link
     * java.nio.file.Files#newDirectoryStream(Path) newDirectoryStream} method to
     * open a directory and iterate over the names of the files in the directory.
     * This may use less resources when working with very large directories, and
     * may be more responsive when working with remote directories.
     *
     * @return  An array of strings naming the files and directories in the
     *          directory denoted by this abstract pathname.  The array will be
     *          empty if the directory is empty.  Returns {@code null} if
     *          this abstract pathname does not denote a directory, or if an
     *          I/O error occurs.
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          SecurityManager#checkRead(String)} method denies read access to
     *          the directory
     */
    public String[] list() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkRead(path);
        }
        if (isInvalid()) {
            return null;
        }
        return fs.list(this);
    }

    
Returns an array of strings naming the files and directories in the directory denoted by this abstract pathname that satisfy the specified filter. The behavior of this method is the same as that of the list() method, except that the strings in the returned array must satisfy the filter. If the given filter is null then all names are accepted. Otherwise, a name satisfies the filter if and only if the value true results when the FilenameFilter.accept(File, String) method of the filter is invoked on this abstract pathname and the name of a file or directory in the directory that it denotes. 
Params:
filter – 
        A filename filter
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkRead(String) method denies read access to the directory
See Also:
Files.newDirectoryStream(Path, String)
Returns:
 An array of strings naming the files and directories in the directory denoted by this abstract pathname that were accepted by the given filter. The array will be empty if the directory is empty or if no names were accepted by the filter. Returns null if this abstract pathname does not denote a directory, or if an I/O error occurs./**
     * Returns an array of strings naming the files and directories in the
     * directory denoted by this abstract pathname that satisfy the specified
     * filter.  The behavior of this method is the same as that of the
     * {@link #list()} method, except that the strings in the returned array
     * must satisfy the filter.  If the given {@code filter} is {@code null}
     * then all names are accepted.  Otherwise, a name satisfies the filter if
     * and only if the value {@code true} results when the {@link
     * FilenameFilter#accept FilenameFilter.accept(File,&nbsp;String)} method
     * of the filter is invoked on this abstract pathname and the name of a
     * file or directory in the directory that it denotes.
     *
     * @param  filter
     *         A filename filter
     *
     * @return  An array of strings naming the files and directories in the
     *          directory denoted by this abstract pathname that were accepted
     *          by the given {@code filter}.  The array will be empty if the
     *          directory is empty or if no names were accepted by the filter.
     *          Returns {@code null} if this abstract pathname does not denote
     *          a directory, or if an I/O error occurs.
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          SecurityManager#checkRead(String)} method denies read access to
     *          the directory
     *
     * @see java.nio.file.Files#newDirectoryStream(Path,String)
     */
    public String[] list(FilenameFilter filter) {
        String names[] = list();
        if ((names == null) || (filter == null)) {
            return names;
        }
        List<String> v = new ArrayList<>();
        for (int i = 0 ; i < names.length ; i++) {
            if (filter.accept(this, names[i])) {
                v.add(names[i]);
            }
        }
        return v.toArray(new String[v.size()]);
    }

    
Returns an array of abstract pathnames denoting the files in the
directory denoted by this abstract pathname.
 If this abstract pathname does not denote a directory, then this method returns null. Otherwise an array of File objects is returned, one for each file or directory in the directory. Pathnames denoting the directory itself and the directory's parent directory are not included in the result. Each resulting abstract pathname is constructed from this abstract pathname using the File(File, String) constructor. Therefore if this pathname is absolute then each resulting pathname is absolute; if this pathname is relative then each resulting pathname will be relative to the same directory. 
 There is no guarantee that the name strings in the resulting array
will appear in any specific order; they are not, in particular,
guaranteed to appear in alphabetical order.
 Note that the Files class defines the newDirectoryStream method to open a directory and iterate over the names of the files in the directory. This may use less resources when working with very large directories. 
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkRead(String) method denies read access to the directory
Returns:
 An array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname. The array will be empty if the directory is empty. Returns null if this abstract pathname does not denote a directory, or if an I/O error occurs.
Since:
 1.2/**
     * Returns an array of abstract pathnames denoting the files in the
     * directory denoted by this abstract pathname.
     *
     * <p> If this abstract pathname does not denote a directory, then this
     * method returns {@code null}.  Otherwise an array of {@code File} objects
     * is returned, one for each file or directory in the directory.  Pathnames
     * denoting the directory itself and the directory's parent directory are
     * not included in the result.  Each resulting abstract pathname is
     * constructed from this abstract pathname using the {@link #File(File,
     * String) File(File,&nbsp;String)} constructor.  Therefore if this
     * pathname is absolute then each resulting pathname is absolute; if this
     * pathname is relative then each resulting pathname will be relative to
     * the same directory.
     *
     * <p> There is no guarantee that the name strings in the resulting array
     * will appear in any specific order; they are not, in particular,
     * guaranteed to appear in alphabetical order.
     *
     * <p> Note that the {@link java.nio.file.Files} class defines the {@link
     * java.nio.file.Files#newDirectoryStream(Path) newDirectoryStream} method
     * to open a directory and iterate over the names of the files in the
     * directory. This may use less resources when working with very large
     * directories.
     *
     * @return  An array of abstract pathnames denoting the files and
     *          directories in the directory denoted by this abstract pathname.
     *          The array will be empty if the directory is empty.  Returns
     *          {@code null} if this abstract pathname does not denote a
     *          directory, or if an I/O error occurs.
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          SecurityManager#checkRead(String)} method denies read access to
     *          the directory
     *
     * @since  1.2
     */
    public File[] listFiles() {
        String[] ss = list();
        if (ss == null) return null;
        int n = ss.length;
        File[] fs = new File[n];
        for (int i = 0; i < n; i++) {
            fs[i] = new File(ss[i], this);
        }
        return fs;
    }

    
Returns an array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname that satisfy the specified filter. The behavior of this method is the same as that of the listFiles() method, except that the pathnames in the returned array must satisfy the filter. If the given filter is null then all pathnames are accepted. Otherwise, a pathname satisfies the filter if and only if the value true results when the 
FilenameFilter.accept(File, String) method of the filter is invoked on this abstract pathname and the name of a file or directory in the directory that it denotes. 
Params:
filter – 
        A filename filter
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkRead(String) method denies read access to the directory
See Also:
Files.newDirectoryStream(Path, String)
Returns:
 An array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname. The array will be empty if the directory is empty. Returns null if this abstract pathname does not denote a directory, or if an I/O error occurs.
Since:
 1.2/**
     * Returns an array of abstract pathnames denoting the files and
     * directories in the directory denoted by this abstract pathname that
     * satisfy the specified filter.  The behavior of this method is the same
     * as that of the {@link #listFiles()} method, except that the pathnames in
     * the returned array must satisfy the filter.  If the given {@code filter}
     * is {@code null} then all pathnames are accepted.  Otherwise, a pathname
     * satisfies the filter if and only if the value {@code true} results when
     * the {@link FilenameFilter#accept
     * FilenameFilter.accept(File,&nbsp;String)} method of the filter is
     * invoked on this abstract pathname and the name of a file or directory in
     * the directory that it denotes.
     *
     * @param  filter
     *         A filename filter
     *
     * @return  An array of abstract pathnames denoting the files and
     *          directories in the directory denoted by this abstract pathname.
     *          The array will be empty if the directory is empty.  Returns
     *          {@code null} if this abstract pathname does not denote a
     *          directory, or if an I/O error occurs.
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          SecurityManager#checkRead(String)} method denies read access to
     *          the directory
     *
     * @since  1.2
     * @see java.nio.file.Files#newDirectoryStream(Path,String)
     */
    public File[] listFiles(FilenameFilter filter) {
        String ss[] = list();
        if (ss == null) return null;
        ArrayList<File> files = new ArrayList<>();
        for (String s : ss)
            if ((filter == null) || filter.accept(this, s))
                files.add(new File(s, this));
        return files.toArray(new File[files.size()]);
    }

    
Returns an array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname that satisfy the specified filter. The behavior of this method is the same as that of the listFiles() method, except that the pathnames in the returned array must satisfy the filter. If the given filter is null then all pathnames are accepted. Otherwise, a pathname satisfies the filter if and only if the value true results when the FileFilter.accept(File) method of the filter is invoked on the pathname. 
Params:
filter – 
        A file filter
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkRead(String) method denies read access to the directory
See Also:
Files.newDirectoryStream(Path, Filter<? super Path>)
Returns:
 An array of abstract pathnames denoting the files and directories in the directory denoted by this abstract pathname. The array will be empty if the directory is empty. Returns null if this abstract pathname does not denote a directory, or if an I/O error occurs.
Since:
 1.2/**
     * Returns an array of abstract pathnames denoting the files and
     * directories in the directory denoted by this abstract pathname that
     * satisfy the specified filter.  The behavior of this method is the same
     * as that of the {@link #listFiles()} method, except that the pathnames in
     * the returned array must satisfy the filter.  If the given {@code filter}
     * is {@code null} then all pathnames are accepted.  Otherwise, a pathname
     * satisfies the filter if and only if the value {@code true} results when
     * the {@link FileFilter#accept FileFilter.accept(File)} method of the
     * filter is invoked on the pathname.
     *
     * @param  filter
     *         A file filter
     *
     * @return  An array of abstract pathnames denoting the files and
     *          directories in the directory denoted by this abstract pathname.
     *          The array will be empty if the directory is empty.  Returns
     *          {@code null} if this abstract pathname does not denote a
     *          directory, or if an I/O error occurs.
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          SecurityManager#checkRead(String)} method denies read access to
     *          the directory
     *
     * @since  1.2
     * @see java.nio.file.Files#newDirectoryStream(Path,java.nio.file.DirectoryStream.Filter)
     */
    public File[] listFiles(FileFilter filter) {
        String ss[] = list();
        if (ss == null) return null;
        ArrayList<File> files = new ArrayList<>();
        for (String s : ss) {
            File f = new File(s, this);
            if ((filter == null) || filter.accept(f))
                files.add(f);
        }
        return files.toArray(new File[files.size()]);
    }

    
Creates the directory named by this abstract pathname.
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkWrite(String) method does not permit the named directory to be created
Returns:
 true if and only if the directory was
         created; false otherwise/**
     * Creates the directory named by this abstract pathname.
     *
     * @return  <code>true</code> if and only if the directory was
     *          created; <code>false</code> otherwise
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkWrite(java.lang.String)}
     *          method does not permit the named directory to be created
     */
    public boolean mkdir() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkWrite(path);
        }
        if (isInvalid()) {
            return false;
        }
        return fs.createDirectory(this);
    }

    
Creates the directory named by this abstract pathname, including any
necessary but nonexistent parent directories.  Note that if this
operation fails it may have succeeded in creating some of the necessary
parent directories.
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkRead(String) method does not permit verification of the existence of the named directory and all necessary parent directories; or if the SecurityManager.checkWrite(String) method does not permit the named directory and all necessary parent directories to be created
Returns:
 true if and only if the directory was created,
         along with all necessary parent directories; false
         otherwise/**
     * Creates the directory named by this abstract pathname, including any
     * necessary but nonexistent parent directories.  Note that if this
     * operation fails it may have succeeded in creating some of the necessary
     * parent directories.
     *
     * @return  <code>true</code> if and only if the directory was created,
     *          along with all necessary parent directories; <code>false</code>
     *          otherwise
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkRead(java.lang.String)}
     *          method does not permit verification of the existence of the
     *          named directory and all necessary parent directories; or if
     *          the {@link
     *          java.lang.SecurityManager#checkWrite(java.lang.String)}
     *          method does not permit the named directory and all necessary
     *          parent directories to be created
     */
    public boolean mkdirs() {
        if (exists()) {
            return false;
        }
        if (mkdir()) {
            return true;
        }
        File canonFile = null;
        try {
            canonFile = getCanonicalFile();
        } catch (IOException e) {
            return false;
        }

        File parent = canonFile.getParentFile();
        return (parent != null && (parent.mkdirs() || parent.exists()) &&
                canonFile.mkdir());
    }

    
Renames the file denoted by this abstract pathname.
 Many aspects of the behavior of this method are inherently
platform-dependent: The rename operation might not be able to move a
file from one filesystem to another, it might not be atomic, and it
might not succeed if a file with the destination abstract pathname
already exists.  The return value should always be checked to make sure
that the rename operation was successful.
 Note that the Files class defines the move method to move or rename a file in a platform independent manner. 
Params:
dest –  The new abstract pathname for the named file
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkWrite(String) method denies write access to either the old or new pathnames
NullPointerException – 
         If parameter dest is null
Returns:
 true if and only if the renaming succeeded;
         false otherwise/**
     * Renames the file denoted by this abstract pathname.
     *
     * <p> Many aspects of the behavior of this method are inherently
     * platform-dependent: The rename operation might not be able to move a
     * file from one filesystem to another, it might not be atomic, and it
     * might not succeed if a file with the destination abstract pathname
     * already exists.  The return value should always be checked to make sure
     * that the rename operation was successful.
     *
     * <p> Note that the {@link java.nio.file.Files} class defines the {@link
     * java.nio.file.Files#move move} method to move or rename a file in a
     * platform independent manner.
     *
     * @param  dest  The new abstract pathname for the named file
     *
     * @return  <code>true</code> if and only if the renaming succeeded;
     *          <code>false</code> otherwise
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkWrite(java.lang.String)}
     *          method denies write access to either the old or new pathnames
     *
     * @throws  NullPointerException
     *          If parameter <code>dest</code> is <code>null</code>
     */
    public boolean renameTo(File dest) {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkWrite(path);
            security.checkWrite(dest.path);
        }
        if (dest == null) {
            throw new NullPointerException();
        }
        if (this.isInvalid() || dest.isInvalid()) {
            return false;
        }
        return fs.rename(this, dest);
    }

    
Sets the last-modified time of the file or directory named by this
abstract pathname.
 All platforms support file-modification times to the nearest second, but some provide more precision. The argument will be truncated to fit the supported precision. If the operation succeeds and no intervening operations on the file take place, then the next invocation of the lastModified method will return the (possibly truncated) time argument that was passed to this method.
Params:
time –  The new last-modified time, measured in milliseconds since
              the epoch (00:00:00 GMT, January 1, 1970)
Throws:
IllegalArgumentException –  If the argument is negative
SecurityException –  If a security manager exists and its SecurityManager.checkWrite(String) method denies write access to the named file
Returns:
true if and only if the operation succeeded;
         false otherwise
Since:
1.2/**
     * Sets the last-modified time of the file or directory named by this
     * abstract pathname.
     *
     * <p> All platforms support file-modification times to the nearest second,
     * but some provide more precision.  The argument will be truncated to fit
     * the supported precision.  If the operation succeeds and no intervening
     * operations on the file take place, then the next invocation of the
     * {@link #lastModified} method will return the (possibly
     * truncated) <code>time</code> argument that was passed to this method.
     *
     * @param  time  The new last-modified time, measured in milliseconds since
     *               the epoch (00:00:00 GMT, January 1, 1970)
     *
     * @return <code>true</code> if and only if the operation succeeded;
     *          <code>false</code> otherwise
     *
     * @throws  IllegalArgumentException  If the argument is negative
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkWrite(java.lang.String)}
     *          method denies write access to the named file
     *
     * @since 1.2
     */
    public boolean setLastModified(long time) {
        if (time < 0) throw new IllegalArgumentException("Negative time");
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkWrite(path);
        }
        if (isInvalid()) {
            return false;
        }
        return fs.setLastModifiedTime(this, time);
    }

    
Marks the file or directory named by this abstract pathname so that
only read operations are allowed. After invoking this method the file
or directory will not change until it is either deleted or marked
to allow write access. On some platforms it may be possible to start the
Java virtual machine with special privileges that allow it to modify
files that are marked read-only. Whether or not a read-only file or
directory may be deleted depends upon the underlying system.
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkWrite(String) method denies write access to the named file
Returns:
true if and only if the operation succeeded;
         false otherwise
Since:
1.2/**
     * Marks the file or directory named by this abstract pathname so that
     * only read operations are allowed. After invoking this method the file
     * or directory will not change until it is either deleted or marked
     * to allow write access. On some platforms it may be possible to start the
     * Java virtual machine with special privileges that allow it to modify
     * files that are marked read-only. Whether or not a read-only file or
     * directory may be deleted depends upon the underlying system.
     *
     * @return <code>true</code> if and only if the operation succeeded;
     *          <code>false</code> otherwise
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkWrite(java.lang.String)}
     *          method denies write access to the named file
     *
     * @since 1.2
     */
    public boolean setReadOnly() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkWrite(path);
        }
        if (isInvalid()) {
            return false;
        }
        return fs.setReadOnly(this);
    }

    
Sets the owner's or everybody's write permission for this abstract
pathname. On some platforms it may be possible to start the Java virtual
machine with special privileges that allow it to modify files that
disallow write operations.
 The Files class defines methods that operate on file attributes including file permissions. This may be used when finer manipulation of file permissions is required. 
Params:
writable – 
         If true, sets the access permission to allow write
         operations; if false to disallow write operations
ownerOnly – 
         If true, the write permission applies only to the
         owner's write permission; otherwise, it applies to everybody.  If
         the underlying file system can not distinguish the owner's write
         permission from that of others, then the permission will apply to
         everybody, regardless of this value.
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkWrite(String) method denies write access to the named file
Returns:
 true if and only if the operation succeeded. The
         operation will fail if the user does not have permission to change
         the access permissions of this abstract pathname.
Since:
1.6/**
     * Sets the owner's or everybody's write permission for this abstract
     * pathname. On some platforms it may be possible to start the Java virtual
     * machine with special privileges that allow it to modify files that
     * disallow write operations.
     *
     * <p> The {@link java.nio.file.Files} class defines methods that operate on
     * file attributes including file permissions. This may be used when finer
     * manipulation of file permissions is required.
     *
     * @param   writable
     *          If <code>true</code>, sets the access permission to allow write
     *          operations; if <code>false</code> to disallow write operations
     *
     * @param   ownerOnly
     *          If <code>true</code>, the write permission applies only to the
     *          owner's write permission; otherwise, it applies to everybody.  If
     *          the underlying file system can not distinguish the owner's write
     *          permission from that of others, then the permission will apply to
     *          everybody, regardless of this value.
     *
     * @return  <code>true</code> if and only if the operation succeeded. The
     *          operation will fail if the user does not have permission to change
     *          the access permissions of this abstract pathname.
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkWrite(java.lang.String)}
     *          method denies write access to the named file
     *
     * @since 1.6
     */
    public boolean setWritable(boolean writable, boolean ownerOnly) {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkWrite(path);
        }
        if (isInvalid()) {
            return false;
        }
        return fs.setPermission(this, FileSystem.ACCESS_WRITE, writable, ownerOnly);
    }

    
A convenience method to set the owner's write permission for this abstract
pathname. On some platforms it may be possible to start the Java virtual
machine with special privileges that allow it to modify files that
disallow write operations.
 An invocation of this method of the form file.setWritable(arg) behaves in exactly the same way as the invocation 

    file.setWritable(arg, true)

Params:
writable – 
         If true, sets the access permission to allow write
         operations; if false to disallow write operations
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkWrite(String) method denies write access to the file
Returns:
 true if and only if the operation succeeded.  The
         operation will fail if the user does not have permission to
         change the access permissions of this abstract pathname.
Since:
1.6/**
     * A convenience method to set the owner's write permission for this abstract
     * pathname. On some platforms it may be possible to start the Java virtual
     * machine with special privileges that allow it to modify files that
     * disallow write operations.
     *
     * <p> An invocation of this method of the form {@code file.setWritable(arg)}
     * behaves in exactly the same way as the invocation
     *
     * <pre>{@code
     *     file.setWritable(arg, true)
     * }</pre>
     *
     * @param   writable
     *          If <code>true</code>, sets the access permission to allow write
     *          operations; if <code>false</code> to disallow write operations
     *
     * @return  <code>true</code> if and only if the operation succeeded.  The
     *          operation will fail if the user does not have permission to
     *          change the access permissions of this abstract pathname.
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkWrite(java.lang.String)}
     *          method denies write access to the file
     *
     * @since 1.6
     */
    public boolean setWritable(boolean writable) {
        return setWritable(writable, true);
    }

    
Sets the owner's or everybody's read permission for this abstract
pathname. On some platforms it may be possible to start the Java virtual
machine with special privileges that allow it to read files that are
marked as unreadable.
 The Files class defines methods that operate on file attributes including file permissions. This may be used when finer manipulation of file permissions is required. 
Params:
readable – 
         If true, sets the access permission to allow read
         operations; if false to disallow read operations
ownerOnly – 
         If true, the read permission applies only to the
         owner's read permission; otherwise, it applies to everybody.  If
         the underlying file system can not distinguish the owner's read
         permission from that of others, then the permission will apply to
         everybody, regardless of this value.
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkWrite(String) method denies write access to the file
Returns:
 true if and only if the operation succeeded.  The
         operation will fail if the user does not have permission to
         change the access permissions of this abstract pathname.  If
         readable is false and the underlying
         file system does not implement a read permission, then the
         operation will fail.
Since:
1.6/**
     * Sets the owner's or everybody's read permission for this abstract
     * pathname. On some platforms it may be possible to start the Java virtual
     * machine with special privileges that allow it to read files that are
     * marked as unreadable.
     *
     * <p> The {@link java.nio.file.Files} class defines methods that operate on
     * file attributes including file permissions. This may be used when finer
     * manipulation of file permissions is required.
     *
     * @param   readable
     *          If <code>true</code>, sets the access permission to allow read
     *          operations; if <code>false</code> to disallow read operations
     *
     * @param   ownerOnly
     *          If <code>true</code>, the read permission applies only to the
     *          owner's read permission; otherwise, it applies to everybody.  If
     *          the underlying file system can not distinguish the owner's read
     *          permission from that of others, then the permission will apply to
     *          everybody, regardless of this value.
     *
     * @return  <code>true</code> if and only if the operation succeeded.  The
     *          operation will fail if the user does not have permission to
     *          change the access permissions of this abstract pathname.  If
     *          <code>readable</code> is <code>false</code> and the underlying
     *          file system does not implement a read permission, then the
     *          operation will fail.
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkWrite(java.lang.String)}
     *          method denies write access to the file
     *
     * @since 1.6
     */
    public boolean setReadable(boolean readable, boolean ownerOnly) {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkWrite(path);
        }
        if (isInvalid()) {
            return false;
        }
        return fs.setPermission(this, FileSystem.ACCESS_READ, readable, ownerOnly);
    }

    
A convenience method to set the owner's read permission for this abstract
pathname. On some platforms it may be possible to start the Java virtual
machine with special privileges that allow it to read files that are
marked as unreadable.
An invocation of this method of the form file.setReadable(arg) behaves in exactly the same way as the invocation 

    file.setReadable(arg, true)

Params:
readable – 
         If true, sets the access permission to allow read
         operations; if false to disallow read operations
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkWrite(String) method denies write access to the file
Returns:
 true if and only if the operation succeeded.  The
         operation will fail if the user does not have permission to
         change the access permissions of this abstract pathname.  If
         readable is false and the underlying
         file system does not implement a read permission, then the
         operation will fail.
Since:
1.6/**
     * A convenience method to set the owner's read permission for this abstract
     * pathname. On some platforms it may be possible to start the Java virtual
     * machine with special privileges that allow it to read files that are
     * marked as unreadable.
     *
     * <p>An invocation of this method of the form {@code file.setReadable(arg)}
     * behaves in exactly the same way as the invocation
     *
     * <pre>{@code
     *     file.setReadable(arg, true)
     * }</pre>
     *
     * @param  readable
     *          If <code>true</code>, sets the access permission to allow read
     *          operations; if <code>false</code> to disallow read operations
     *
     * @return  <code>true</code> if and only if the operation succeeded.  The
     *          operation will fail if the user does not have permission to
     *          change the access permissions of this abstract pathname.  If
     *          <code>readable</code> is <code>false</code> and the underlying
     *          file system does not implement a read permission, then the
     *          operation will fail.
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkWrite(java.lang.String)}
     *          method denies write access to the file
     *
     * @since 1.6
     */
    public boolean setReadable(boolean readable) {
        return setReadable(readable, true);
    }

    
Sets the owner's or everybody's execute permission for this abstract
pathname. On some platforms it may be possible to start the Java virtual
machine with special privileges that allow it to execute files that are
not marked executable.
 The Files class defines methods that operate on file attributes including file permissions. This may be used when finer manipulation of file permissions is required. 
Params:
executable – 
         If true, sets the access permission to allow execute
         operations; if false to disallow execute operations
ownerOnly – 
         If true, the execute permission applies only to the
         owner's execute permission; otherwise, it applies to everybody.
         If the underlying file system can not distinguish the owner's
         execute permission from that of others, then the permission will
         apply to everybody, regardless of this value.
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkWrite(String) method denies write access to the file
Returns:
 true if and only if the operation succeeded.  The
         operation will fail if the user does not have permission to
         change the access permissions of this abstract pathname.  If
         executable is false and the underlying
         file system does not implement an execute permission, then the
         operation will fail.
Since:
1.6/**
     * Sets the owner's or everybody's execute permission for this abstract
     * pathname. On some platforms it may be possible to start the Java virtual
     * machine with special privileges that allow it to execute files that are
     * not marked executable.
     *
     * <p> The {@link java.nio.file.Files} class defines methods that operate on
     * file attributes including file permissions. This may be used when finer
     * manipulation of file permissions is required.
     *
     * @param   executable
     *          If <code>true</code>, sets the access permission to allow execute
     *          operations; if <code>false</code> to disallow execute operations
     *
     * @param   ownerOnly
     *          If <code>true</code>, the execute permission applies only to the
     *          owner's execute permission; otherwise, it applies to everybody.
     *          If the underlying file system can not distinguish the owner's
     *          execute permission from that of others, then the permission will
     *          apply to everybody, regardless of this value.
     *
     * @return  <code>true</code> if and only if the operation succeeded.  The
     *          operation will fail if the user does not have permission to
     *          change the access permissions of this abstract pathname.  If
     *          <code>executable</code> is <code>false</code> and the underlying
     *          file system does not implement an execute permission, then the
     *          operation will fail.
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkWrite(java.lang.String)}
     *          method denies write access to the file
     *
     * @since 1.6
     */
    public boolean setExecutable(boolean executable, boolean ownerOnly) {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkWrite(path);
        }
        if (isInvalid()) {
            return false;
        }
        return fs.setPermission(this, FileSystem.ACCESS_EXECUTE, executable, ownerOnly);
    }

    
A convenience method to set the owner's execute permission for this
abstract pathname. On some platforms it may be possible to start the Java
virtual machine with special privileges that allow it to execute files
that are not marked executable.
An invocation of this method of the form file.setExcutable(arg) behaves in exactly the same way as the invocation 

    file.setExecutable(arg, true)

Params:
executable – 
         If true, sets the access permission to allow execute
         operations; if false to disallow execute operations
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkWrite(String) method denies write access to the file
Returns:
  true if and only if the operation succeeded.  The
          operation will fail if the user does not have permission to
          change the access permissions of this abstract pathname.  If
          executable is false and the underlying
          file system does not implement an execute permission, then the
          operation will fail.
Since:
1.6/**
     * A convenience method to set the owner's execute permission for this
     * abstract pathname. On some platforms it may be possible to start the Java
     * virtual machine with special privileges that allow it to execute files
     * that are not marked executable.
     *
     * <p>An invocation of this method of the form {@code file.setExcutable(arg)}
     * behaves in exactly the same way as the invocation
     *
     * <pre>{@code
     *     file.setExecutable(arg, true)
     * }</pre>
     *
     * @param   executable
     *          If <code>true</code>, sets the access permission to allow execute
     *          operations; if <code>false</code> to disallow execute operations
     *
     * @return   <code>true</code> if and only if the operation succeeded.  The
     *           operation will fail if the user does not have permission to
     *           change the access permissions of this abstract pathname.  If
     *           <code>executable</code> is <code>false</code> and the underlying
     *           file system does not implement an execute permission, then the
     *           operation will fail.
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkWrite(java.lang.String)}
     *          method denies write access to the file
     *
     * @since 1.6
     */
    public boolean setExecutable(boolean executable) {
        return setExecutable(executable, true);
    }

    
Tests whether the application can execute the file denoted by this abstract pathname. On some platforms it may be possible to start the Java virtual machine with special privileges that allow it to execute files that are not marked executable. Consequently this method may return true even though the file does not have execute permissions. 
Throws:
SecurityException –  If a security manager exists and its SecurityManager.checkExec(String) method denies execute access to the file
Returns:
 true if and only if the abstract pathname exists
         and the application is allowed to execute the file
Since:
1.6/**
     * Tests whether the application can execute the file denoted by this
     * abstract pathname. On some platforms it may be possible to start the
     * Java virtual machine with special privileges that allow it to execute
     * files that are not marked executable. Consequently this method may return
     * {@code true} even though the file does not have execute permissions.
     *
     * @return  <code>true</code> if and only if the abstract pathname exists
     *          <em>and</em> the application is allowed to execute the file
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkExec(java.lang.String)}
     *          method denies execute access to the file
     *
     * @since 1.6
     */
    public boolean canExecute() {
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkExec(path);
        }
        if (isInvalid()) {
            return false;
        }
        return fs.checkAccess(this, FileSystem.ACCESS_EXECUTE);
    }


    /* -- Filesystem interface -- */

    
List the available filesystem roots.
 A particular Java platform may support zero or more hierarchically-organized file systems. Each file system has a root directory from which all other files in that file system can be reached. Windows platforms, for example, have a root directory for each active drive; UNIX platforms have a single root directory, namely "/". The set of available filesystem roots is affected by various system-level operations such as the insertion or ejection of removable media and the disconnecting or unmounting of physical or virtual disk drives. 
 This method returns an array of File objects that denote the root directories of the available filesystem roots. It is guaranteed that the canonical pathname of any file physically present on the local machine will begin with one of the roots returned by this method. 
 The canonical pathname of a file that resides on some other machine and is accessed via a remote-filesystem protocol such as SMB or NFS may or may not begin with one of the roots returned by this method. If the pathname of a remote file is syntactically indistinguishable from the pathname of a local file then it will begin with one of the roots returned by this method. Thus, for example, File objects denoting the root directories of the mapped network drives of a Windows platform will be returned by this method, while File objects containing UNC pathnames will not be returned by this method. 
 Unlike most methods in this class, this method does not throw security exceptions. If a security manager exists and its SecurityManager.checkRead(String) method denies read access to a particular root directory, then that directory will not appear in the result. 
See Also:
FileStore
Returns:
 An array of File objects denoting the available filesystem roots, or null if the set of roots could not be determined. The array will be empty if there are no filesystem roots.
Since:
 1.2/**
     * List the available filesystem roots.
     *
     * <p> A particular Java platform may support zero or more
     * hierarchically-organized file systems.  Each file system has a
     * {@code root} directory from which all other files in that file system
     * can be reached.  Windows platforms, for example, have a root directory
     * for each active drive; UNIX platforms have a single root directory,
     * namely {@code "/"}.  The set of available filesystem roots is affected
     * by various system-level operations such as the insertion or ejection of
     * removable media and the disconnecting or unmounting of physical or
     * virtual disk drives.
     *
     * <p> This method returns an array of {@code File} objects that denote the
     * root directories of the available filesystem roots.  It is guaranteed
     * that the canonical pathname of any file physically present on the local
     * machine will begin with one of the roots returned by this method.
     *
     * <p> The canonical pathname of a file that resides on some other machine
     * and is accessed via a remote-filesystem protocol such as SMB or NFS may
     * or may not begin with one of the roots returned by this method.  If the
     * pathname of a remote file is syntactically indistinguishable from the
     * pathname of a local file then it will begin with one of the roots
     * returned by this method.  Thus, for example, {@code File} objects
     * denoting the root directories of the mapped network drives of a Windows
     * platform will be returned by this method, while {@code File} objects
     * containing UNC pathnames will not be returned by this method.
     *
     * <p> Unlike most methods in this class, this method does not throw
     * security exceptions.  If a security manager exists and its {@link
     * SecurityManager#checkRead(String)} method denies read access to a
     * particular root directory, then that directory will not appear in the
     * result.
     *
     * @return  An array of {@code File} objects denoting the available
     *          filesystem roots, or {@code null} if the set of roots could not
     *          be determined.  The array will be empty if there are no
     *          filesystem roots.
     *
     * @since  1.2
     * @see java.nio.file.FileStore
     */
    public static File[] listRoots() {
        return fs.listRoots();
    }


    /* -- Disk usage -- */

    
Returns the size of the partition named by this
abstract pathname.
Throws:
SecurityException –  If a security manager has been installed and it denies RuntimePermission("getFileSystemAttributes") or its SecurityManager.checkRead(String) method denies read access to the file named by this abstract pathname
Returns:
 The size, in bytes, of the partition or 0L if this abstract pathname does not name a partition
Since:
 1.6/**
     * Returns the size of the partition <a href="#partName">named</a> by this
     * abstract pathname.
     *
     * @return  The size, in bytes, of the partition or {@code 0L} if this
     *          abstract pathname does not name a partition
     *
     * @throws  SecurityException
     *          If a security manager has been installed and it denies
     *          {@link RuntimePermission}{@code ("getFileSystemAttributes")}
     *          or its {@link SecurityManager#checkRead(String)} method denies
     *          read access to the file named by this abstract pathname
     *
     * @since  1.6
     */
    public long getTotalSpace() {
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(new RuntimePermission("getFileSystemAttributes"));
            sm.checkRead(path);
        }
        if (isInvalid()) {
            return 0L;
        }
        return fs.getSpace(this, FileSystem.SPACE_TOTAL);
    }

    
Returns the number of unallocated bytes in the partition named by this abstract path name.
 The returned number of unallocated bytes is a hint, but not
a guarantee, that it is possible to use most or any of these
bytes.  The number of unallocated bytes is most likely to be
accurate immediately after this call.  It is likely to be made
inaccurate by any external I/O operations including those made
on the system outside of this virtual machine.  This method
makes no guarantee that write operations to this file system
will succeed.
Throws:
SecurityException –  If a security manager has been installed and it denies RuntimePermission("getFileSystemAttributes") or its SecurityManager.checkRead(String) method denies read access to the file named by this abstract pathname
Returns:
 The number of unallocated bytes on the partition or 0L if the abstract pathname does not name a partition. This value will be less than or equal to the total file system size returned by getTotalSpace.
Since:
 1.6/**
     * Returns the number of unallocated bytes in the partition <a
     * href="#partName">named</a> by this abstract path name.
     *
     * <p> The returned number of unallocated bytes is a hint, but not
     * a guarantee, that it is possible to use most or any of these
     * bytes.  The number of unallocated bytes is most likely to be
     * accurate immediately after this call.  It is likely to be made
     * inaccurate by any external I/O operations including those made
     * on the system outside of this virtual machine.  This method
     * makes no guarantee that write operations to this file system
     * will succeed.
     *
     * @return  The number of unallocated bytes on the partition or {@code 0L}
     *          if the abstract pathname does not name a partition.  This
     *          value will be less than or equal to the total file system size
     *          returned by {@link #getTotalSpace}.
     *
     * @throws  SecurityException
     *          If a security manager has been installed and it denies
     *          {@link RuntimePermission}{@code ("getFileSystemAttributes")}
     *          or its {@link SecurityManager#checkRead(String)} method denies
     *          read access to the file named by this abstract pathname
     *
     * @since  1.6
     */
    public long getFreeSpace() {
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(new RuntimePermission("getFileSystemAttributes"));
            sm.checkRead(path);
        }
        if (isInvalid()) {
            return 0L;
        }
        return fs.getSpace(this, FileSystem.SPACE_FREE);
    }

    
Returns the number of bytes available to this virtual machine on the
partition named by this abstract pathname. When possible, this method checks for write permissions and other operating system restrictions and will therefore usually provide a more accurate estimate of how much new data can actually be written than getFreeSpace. 
 The returned number of available bytes is a hint, but not a
guarantee, that it is possible to use most or any of these bytes.  The
number of unallocated bytes is most likely to be accurate immediately
after this call.  It is likely to be made inaccurate by any external
I/O operations including those made on the system outside of this
virtual machine.  This method makes no guarantee that write operations
to this file system will succeed.
Throws:
SecurityException –  If a security manager has been installed and it denies RuntimePermission("getFileSystemAttributes") or its SecurityManager.checkRead(String) method denies read access to the file named by this abstract pathname
Returns:
 The number of available bytes on the partition or 0L if the abstract pathname does not name a partition. On systems where this information is not available, this method will be equivalent to a call to getFreeSpace.
Since:
 1.6/**
     * Returns the number of bytes available to this virtual machine on the
     * partition <a href="#partName">named</a> by this abstract pathname.  When
     * possible, this method checks for write permissions and other operating
     * system restrictions and will therefore usually provide a more accurate
     * estimate of how much new data can actually be written than {@link
     * #getFreeSpace}.
     *
     * <p> The returned number of available bytes is a hint, but not a
     * guarantee, that it is possible to use most or any of these bytes.  The
     * number of unallocated bytes is most likely to be accurate immediately
     * after this call.  It is likely to be made inaccurate by any external
     * I/O operations including those made on the system outside of this
     * virtual machine.  This method makes no guarantee that write operations
     * to this file system will succeed.
     *
     * @return  The number of available bytes on the partition or {@code 0L}
     *          if the abstract pathname does not name a partition.  On
     *          systems where this information is not available, this method
     *          will be equivalent to a call to {@link #getFreeSpace}.
     *
     * @throws  SecurityException
     *          If a security manager has been installed and it denies
     *          {@link RuntimePermission}{@code ("getFileSystemAttributes")}
     *          or its {@link SecurityManager#checkRead(String)} method denies
     *          read access to the file named by this abstract pathname
     *
     * @since  1.6
     */
    public long getUsableSpace() {
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(new RuntimePermission("getFileSystemAttributes"));
            sm.checkRead(path);
        }
        if (isInvalid()) {
            return 0L;
        }
        return fs.getSpace(this, FileSystem.SPACE_USABLE);
    }

    /* -- Temporary files -- */

    private static class TempDirectory {
        private TempDirectory() { }

        // temporary directory location
        private static final File tmpdir = new File(
                GetPropertyAction.privilegedGetProperty("java.io.tmpdir"));
        static File location() {
            return tmpdir;
        }

        // file name generation
        private static final SecureRandom random = new SecureRandom();
        private static int shortenSubName(int subNameLength, int excess,
            int nameMin) {
            int newLength = Math.max(nameMin, subNameLength - excess);
            if (newLength < subNameLength) {
                return newLength;
            }
            return subNameLength;
        }
        static File generateFile(String prefix, String suffix, File dir)
            throws IOException
        {
            long n = random.nextLong();
            String nus = Long.toUnsignedString(n);

            // Use only the file name from the supplied prefix
            prefix = (new File(prefix)).getName();

            int prefixLength = prefix.length();
            int nusLength = nus.length();
            int suffixLength = suffix.length();;

            String name;
            int nameMax = fs.getNameMax(dir.getPath());
            int excess = prefixLength + nusLength + suffixLength - nameMax;
            if (excess <= 0) {
                name = prefix + nus + suffix;
            } else {
                // Name exceeds the maximum path component length: shorten it

                // Attempt to shorten the prefix length to no less then 3
                prefixLength = shortenSubName(prefixLength, excess, 3);
                excess = prefixLength + nusLength + suffixLength - nameMax;

                if (excess > 0) {
                    // Attempt to shorten the suffix length to no less than
                    // 0 or 4 depending on whether it begins with a dot ('.')
                    suffixLength = shortenSubName(suffixLength, excess,
                        suffix.indexOf(".") == 0 ? 4 : 0);
                    suffixLength = shortenSubName(suffixLength, excess, 3);
                    excess = prefixLength + nusLength + suffixLength - nameMax;
                }

                if (excess > 0 && excess <= nusLength - 5) {
                    // Attempt to shorten the random character string length
                    // to no less than 5
                    nusLength = shortenSubName(nusLength, excess, 5);
                }

                StringBuilder sb =
                    new StringBuilder(prefixLength + nusLength + suffixLength);
                sb.append(prefixLength < prefix.length() ?
                    prefix.substring(0, prefixLength) : prefix);
                sb.append(nusLength < nus.length() ?
                    nus.substring(0, nusLength) : nus);
                sb.append(suffixLength < suffix.length() ?
                    suffix.substring(0, suffixLength) : suffix);
                name = sb.toString();
            }

            // Normalize the path component
            name = fs.normalize(name);

            File f = new File(dir, name);
            if (!name.equals(f.getName()) || f.isInvalid()) {
                if (System.getSecurityManager() != null)
                    throw new IOException("Unable to create temporary file");
                else
                    throw new IOException("Unable to create temporary file, "
                        + name);
            }
            return f;
        }
    }

    
 Creates a new empty file in the specified directory, using the
given prefix and suffix strings to generate its name.  If this method
returns successfully then it is guaranteed that:

 The file denoted by the returned abstract pathname did not exist
     before this method was invoked, and
 Neither this method nor any of its variants will return the same
     abstract pathname again in the current invocation of the virtual
     machine.
 This method provides only part of a temporary-file facility. To arrange for a file created by this method to be deleted automatically, use the deleteOnExit method. 
 The prefix argument must be at least three characters
long.  It is recommended that the prefix be a short, meaningful string
such as "hjb" or "mail".  The
suffix argument may be null, in which case the
suffix ".tmp" will be used.
 To create the new file, the prefix and the suffix may first be
adjusted to fit the limitations of the underlying platform.  If the
prefix is too long then it will be truncated, but its first three
characters will always be preserved.  If the suffix is too long then it
too will be truncated, but if it begins with a period character
('.') then the period and the first three characters
following it will always be preserved.  Once these adjustments have been
made the name of the new file will be generated by concatenating the
prefix, five or more internally-generated characters, and the suffix.
 If the directory argument is null then the
system-dependent default temporary-file directory will be used.  The
default temporary-file directory is specified by the system property
java.io.tmpdir.  On UNIX systems the default value of this
property is typically "/tmp" or "/var/tmp"; on
Microsoft Windows systems it is typically "C:\\WINNT\\TEMP".  A different
value may be given to this system property when the Java virtual machine
is invoked, but programmatic changes to this property are not guaranteed
to have any effect upon the temporary directory used by this method.
Params:
prefix –     The prefix string to be used in generating the file's
                   name; must be at least three characters long
suffix –     The suffix string to be used in generating the file's
                   name; may be null, in which case the
                   suffix ".tmp" will be used
directory –  The directory in which the file is to be created, or
                   null if the default temporary-file
                   directory is to be used
Throws:
IllegalArgumentException – 
         If the prefix argument contains fewer than three
         characters
IOException –  If a file could not be created
SecurityException –  If a security manager exists and its SecurityManager.checkWrite(String) method does not allow a file to be created
Returns:
 An abstract pathname denoting a newly-created empty file
Since:
1.2/**
     * <p> Creates a new empty file in the specified directory, using the
     * given prefix and suffix strings to generate its name.  If this method
     * returns successfully then it is guaranteed that:
     *
     * <ol>
     * <li> The file denoted by the returned abstract pathname did not exist
     *      before this method was invoked, and
     * <li> Neither this method nor any of its variants will return the same
     *      abstract pathname again in the current invocation of the virtual
     *      machine.
     * </ol>
     *
     * This method provides only part of a temporary-file facility.  To arrange
     * for a file created by this method to be deleted automatically, use the
     * {@link #deleteOnExit} method.
     *
     * <p> The <code>prefix</code> argument must be at least three characters
     * long.  It is recommended that the prefix be a short, meaningful string
     * such as <code>"hjb"</code> or <code>"mail"</code>.  The
     * <code>suffix</code> argument may be <code>null</code>, in which case the
     * suffix <code>".tmp"</code> will be used.
     *
     * <p> To create the new file, the prefix and the suffix may first be
     * adjusted to fit the limitations of the underlying platform.  If the
     * prefix is too long then it will be truncated, but its first three
     * characters will always be preserved.  If the suffix is too long then it
     * too will be truncated, but if it begins with a period character
     * (<code>'.'</code>) then the period and the first three characters
     * following it will always be preserved.  Once these adjustments have been
     * made the name of the new file will be generated by concatenating the
     * prefix, five or more internally-generated characters, and the suffix.
     *
     * <p> If the <code>directory</code> argument is <code>null</code> then the
     * system-dependent default temporary-file directory will be used.  The
     * default temporary-file directory is specified by the system property
     * <code>java.io.tmpdir</code>.  On UNIX systems the default value of this
     * property is typically <code>"/tmp"</code> or <code>"/var/tmp"</code>; on
     * Microsoft Windows systems it is typically <code>"C:\\WINNT\\TEMP"</code>.  A different
     * value may be given to this system property when the Java virtual machine
     * is invoked, but programmatic changes to this property are not guaranteed
     * to have any effect upon the temporary directory used by this method.
     *
     * @param  prefix     The prefix string to be used in generating the file's
     *                    name; must be at least three characters long
     *
     * @param  suffix     The suffix string to be used in generating the file's
     *                    name; may be <code>null</code>, in which case the
     *                    suffix <code>".tmp"</code> will be used
     *
     * @param  directory  The directory in which the file is to be created, or
     *                    <code>null</code> if the default temporary-file
     *                    directory is to be used
     *
     * @return  An abstract pathname denoting a newly-created empty file
     *
     * @throws  IllegalArgumentException
     *          If the <code>prefix</code> argument contains fewer than three
     *          characters
     *
     * @throws  IOException  If a file could not be created
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkWrite(java.lang.String)}
     *          method does not allow a file to be created
     *
     * @since 1.2
     */
    public static File createTempFile(String prefix, String suffix,
                                      File directory)
        throws IOException
    {
        if (prefix.length() < 3) {
            throw new IllegalArgumentException("Prefix string \"" + prefix +
                "\" too short: length must be at least 3");
        }
        if (suffix == null)
            suffix = ".tmp";

        File tmpdir = (directory != null) ? directory
                                          : TempDirectory.location();
        SecurityManager sm = System.getSecurityManager();
        File f;
        do {
            f = TempDirectory.generateFile(prefix, suffix, tmpdir);

            if (sm != null) {
                try {
                    sm.checkWrite(f.getPath());
                } catch (SecurityException se) {
                    // don't reveal temporary directory location
                    if (directory == null)
                        throw new SecurityException("Unable to create temporary file");
                    throw se;
                }
            }
        } while ((fs.getBooleanAttributes(f) & FileSystem.BA_EXISTS) != 0);

        if (!fs.createFileExclusively(f.getPath()))
            throw new IOException("Unable to create temporary file");

        return f;
    }

    
Creates an empty file in the default temporary-file directory, using the given prefix and suffix to generate its name. Invoking this method is equivalent to invoking 
createTempFile(prefix, suffix, null). 
 The 
Files.createTempFile method provides an alternative method to create an empty file in the temporary-file directory. Files created by that method may have more restrictive access permissions to files created by this method and so may be more suited to security-sensitive applications. 
Params:
prefix –     The prefix string to be used in generating the file's
                   name; must be at least three characters long
suffix –     The suffix string to be used in generating the file's
                   name; may be null, in which case the
                   suffix ".tmp" will be used
Throws:
IllegalArgumentException – 
         If the prefix argument contains fewer than three
         characters
IOException –  If a file could not be created
SecurityException –  If a security manager exists and its SecurityManager.checkWrite(String) method does not allow a file to be created
See Also:
Files.createTempDirectory(String, FileAttribute[])
Returns:
 An abstract pathname denoting a newly-created empty file
Since:
1.2/**
     * Creates an empty file in the default temporary-file directory, using
     * the given prefix and suffix to generate its name. Invoking this method
     * is equivalent to invoking {@link #createTempFile(java.lang.String,
     * java.lang.String, java.io.File)
     * createTempFile(prefix,&nbsp;suffix,&nbsp;null)}.
     *
     * <p> The {@link
     * java.nio.file.Files#createTempFile(String,String,java.nio.file.attribute.FileAttribute[])
     * Files.createTempFile} method provides an alternative method to create an
     * empty file in the temporary-file directory. Files created by that method
     * may have more restrictive access permissions to files created by this
     * method and so may be more suited to security-sensitive applications.
     *
     * @param  prefix     The prefix string to be used in generating the file's
     *                    name; must be at least three characters long
     *
     * @param  suffix     The suffix string to be used in generating the file's
     *                    name; may be <code>null</code>, in which case the
     *                    suffix <code>".tmp"</code> will be used
     *
     * @return  An abstract pathname denoting a newly-created empty file
     *
     * @throws  IllegalArgumentException
     *          If the <code>prefix</code> argument contains fewer than three
     *          characters
     *
     * @throws  IOException  If a file could not be created
     *
     * @throws  SecurityException
     *          If a security manager exists and its {@link
     *          java.lang.SecurityManager#checkWrite(java.lang.String)}
     *          method does not allow a file to be created
     *
     * @since 1.2
     * @see java.nio.file.Files#createTempDirectory(String,FileAttribute[])
     */
    public static File createTempFile(String prefix, String suffix)
        throws IOException
    {
        return createTempFile(prefix, suffix, null);
    }

    /* -- Basic infrastructure -- */

    
Compares two abstract pathnames lexicographically.  The ordering
defined by this method depends upon the underlying system.  On UNIX
systems, alphabetic case is significant in comparing pathnames; on Microsoft Windows
systems it is not.
Params:
pathname –  The abstract pathname to be compared to this abstract
                   pathname
Returns:
 Zero if the argument is equal to this abstract pathname, a
         value less than zero if this abstract pathname is
         lexicographically less than the argument, or a value greater
         than zero if this abstract pathname is lexicographically
         greater than the argument
Since:
  1.2/**
     * Compares two abstract pathnames lexicographically.  The ordering
     * defined by this method depends upon the underlying system.  On UNIX
     * systems, alphabetic case is significant in comparing pathnames; on Microsoft Windows
     * systems it is not.
     *
     * @param   pathname  The abstract pathname to be compared to this abstract
     *                    pathname
     *
     * @return  Zero if the argument is equal to this abstract pathname, a
     *          value less than zero if this abstract pathname is
     *          lexicographically less than the argument, or a value greater
     *          than zero if this abstract pathname is lexicographically
     *          greater than the argument
     *
     * @since   1.2
     */
    public int compareTo(File pathname) {
        return fs.compare(this, pathname);
    }

    
Tests this abstract pathname for equality with the given object.
Returns true if and only if the argument is not
null and is an abstract pathname that denotes the same file
or directory as this abstract pathname.  Whether or not two abstract
pathnames are equal depends upon the underlying system.  On UNIX
systems, alphabetic case is significant in comparing pathnames; on Microsoft Windows
systems it is not.
Params:
obj –   The object to be compared with this abstract pathname
Returns:
 true if and only if the objects are the same;
         false otherwise/**
     * Tests this abstract pathname for equality with the given object.
     * Returns <code>true</code> if and only if the argument is not
     * <code>null</code> and is an abstract pathname that denotes the same file
     * or directory as this abstract pathname.  Whether or not two abstract
     * pathnames are equal depends upon the underlying system.  On UNIX
     * systems, alphabetic case is significant in comparing pathnames; on Microsoft Windows
     * systems it is not.
     *
     * @param   obj   The object to be compared with this abstract pathname
     *
     * @return  <code>true</code> if and only if the objects are the same;
     *          <code>false</code> otherwise
     */
    public boolean equals(Object obj) {
        if ((obj != null) && (obj instanceof File)) {
            return compareTo((File)obj) == 0;
        }
        return false;
    }

    
Computes a hash code for this abstract pathname.  Because equality of
abstract pathnames is inherently system-dependent, so is the computation
of their hash codes.  On UNIX systems, the hash code of an abstract
pathname is equal to the exclusive or of the hash code
of its pathname string and the decimal value
1234321.  On Microsoft Windows systems, the hash
code is equal to the exclusive or of the hash code of
its pathname string converted to lower case and the decimal
value 1234321.  Locale is not taken into account on
lowercasing the pathname string.
Returns:
 A hash code for this abstract pathname/**
     * Computes a hash code for this abstract pathname.  Because equality of
     * abstract pathnames is inherently system-dependent, so is the computation
     * of their hash codes.  On UNIX systems, the hash code of an abstract
     * pathname is equal to the exclusive <em>or</em> of the hash code
     * of its pathname string and the decimal value
     * <code>1234321</code>.  On Microsoft Windows systems, the hash
     * code is equal to the exclusive <em>or</em> of the hash code of
     * its pathname string converted to lower case and the decimal
     * value <code>1234321</code>.  Locale is not taken into account on
     * lowercasing the pathname string.
     *
     * @return  A hash code for this abstract pathname
     */
    public int hashCode() {
        return fs.hashCode(this);
    }

    
Returns the pathname string of this abstract pathname. This is just the string returned by the getPath method. 
Returns:
 The string form of this abstract pathname/**
     * Returns the pathname string of this abstract pathname.  This is just the
     * string returned by the {@link #getPath} method.
     *
     * @return  The string form of this abstract pathname
     */
    public String toString() {
        return getPath();
    }

    
WriteObject is called to save this filename.
The separator character is saved also so it can be replaced
in case the path is reconstituted on a different host type.
@serialData
 Default fields followed by separator character./**
     * WriteObject is called to save this filename.
     * The separator character is saved also so it can be replaced
     * in case the path is reconstituted on a different host type.
     *
     * @serialData  Default fields followed by separator character.
     */
    private synchronized void writeObject(java.io.ObjectOutputStream s)
        throws IOException
    {
        s.defaultWriteObject();
        s.writeChar(separatorChar); // Add the separator character
    }

    
readObject is called to restore this filename.
The original separator character is read.  If it is different
than the separator character on this system, then the old separator
is replaced by the local separator.
/**
     * readObject is called to restore this filename.
     * The original separator character is read.  If it is different
     * than the separator character on this system, then the old separator
     * is replaced by the local separator.
     */
    private synchronized void readObject(java.io.ObjectInputStream s)
         throws IOException, ClassNotFoundException
    {
        ObjectInputStream.GetField fields = s.readFields();
        String pathField = (String)fields.get("path", null);
        char sep = s.readChar(); // read the previous separator char
        if (sep != separatorChar)
            pathField = pathField.replace(sep, separatorChar);
        String path = fs.normalize(pathField);
        UNSAFE.putObject(this, PATH_OFFSET, path);
        UNSAFE.putIntVolatile(this, PREFIX_LENGTH_OFFSET, fs.prefixLength(path));
    }

    private static final long PATH_OFFSET;
    private static final long PREFIX_LENGTH_OFFSET;
    private static final jdk.internal.misc.Unsafe UNSAFE;
    static {
        try {
            jdk.internal.misc.Unsafe unsafe = jdk.internal.misc.Unsafe.getUnsafe();
            PATH_OFFSET = unsafe.objectFieldOffset(
                    File.class.getDeclaredField("path"));
            PREFIX_LENGTH_OFFSET = unsafe.objectFieldOffset(
                    File.class.getDeclaredField("prefixLength"));
            UNSAFE = unsafe;
        } catch (ReflectiveOperationException e) {
            throw new Error(e);
        }
    }


    
use serialVersionUID from JDK 1.0.2 for interoperability /** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = 301077366599181567L;

    // -- Integration with java.nio.file --

    private transient volatile Path filePath;

    
Returns a java.nio.file.Path object constructed from the this abstract path. The resulting Path is associated with the default-filesystem. 
 The first invocation of this method works as if invoking it were
equivalent to evaluating the expression:
FileSystems.getDefault().getPath(this.getPath()); 
 Subsequent invocations of this method return the same Path. 
 If this abstract pathname is the empty abstract pathname then this method returns a Path that may be used to access the current user directory. 
Throws:
InvalidPathException –  if a Path object cannot be constructed from the abstract path (see FileSystem.getPath)
See Also:
Path.toFile
Returns:
 a Path constructed from this abstract path
Since:
  1.7/**
     * Returns a {@link Path java.nio.file.Path} object constructed from the
     * this abstract path. The resulting {@code Path} is associated with the
     * {@link java.nio.file.FileSystems#getDefault default-filesystem}.
     *
     * <p> The first invocation of this method works as if invoking it were
     * equivalent to evaluating the expression:
     * <blockquote><pre>
     * {@link java.nio.file.FileSystems#getDefault FileSystems.getDefault}().{@link
     * java.nio.file.FileSystem#getPath getPath}(this.{@link #getPath getPath}());
     * </pre></blockquote>
     * Subsequent invocations of this method return the same {@code Path}.
     *
     * <p> If this abstract pathname is the empty abstract pathname then this
     * method returns a {@code Path} that may be used to access the current
     * user directory.
     *
     * @return  a {@code Path} constructed from this abstract path
     *
     * @throws  java.nio.file.InvalidPathException
     *          if a {@code Path} object cannot be constructed from the abstract
     *          path (see {@link java.nio.file.FileSystem#getPath FileSystem.getPath})
     *
     * @since   1.7
     * @see Path#toFile
     */
    public Path toPath() {
        Path result = filePath;
        if (result == null) {
            synchronized (this) {
                result = filePath;
                if (result == null) {
                    result = FileSystems.getDefault().getPath(path);
                    filePath = result;
                }
            }
        }
        return result;
    }
}