/*
 * @(#)File.java	1.98 01/03/22
 *
 * Copyright 1994-2001 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the proprietary information of Sun Microsystems, Inc.  
 * Use is subject to license terms.
 * 
 */

package java.io;

import java.net.URL;
import java.net.MalformedURLException;
import java.util.ArrayList;
import java.util.Map;
import java.util.Hashtable;
import java.util.Random;
import java.security.AccessController;
import java.security.AccessControlException;
import sun.security.action.GetPropertyAction;

/**
 * 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,<br>
 *      such as a disk-drive specifier, <code>"/"</code> for the UNIX root
 *      directory, or <code>"\\"</code> for a Win32 UNC pathname, and
 * <li> A sequence of zero or more string <em>names</em>.
 * </ol>
 *
 * Each name in an abstract pathname except for the last 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 <code>{@link
 * #separator}</code> and <code>{@link #separatorChar}</code> 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 prefix concept is used to handle root directories on UNIX platforms,
 * and drive specifiers, root directories and UNC pathnames on Win32 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 Win32 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 the <code>File</code> class are immutable; that is, once
 * created, the abstract pathname represented by a <code>File</code> object
 * will never change.
 *
 * @version 1.98, 03/22/01
 * @author  unascribed
 * @since   JDK1.0
 */

public class File implements java.io.Serializable, Comparable {

    /**
     * The FileSystem object representing the platform's local file system.
     */
    static private FileSystem fs = FileSystem.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
     */
    private String path;

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

    /**
     * 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 <code>file.separator</code>.  On UNIX systems the value of this
     * field is <code>'/'</code> on Win32 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
     * <code>{@link #separatorChar}</code>.
     */
    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 <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 Win32 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
     * <code>{@link #pathSeparatorChar}</code>.
     */
    public static final String pathSeparator = "" + pathSeparatorChar;


    /* -- Constructors -- */

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

    /**
     * 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 Win32 it is "\\".  This is required for
       compatibility with the original behavior of this class. */

    /**
     * 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 <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);
    }


    /* -- 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.
     *
     * @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
     * <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 <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 {@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 <code>"/"</code>.  On Win32 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.
     *
     * <p> If this abstract pathname is already absolute, then the pathname
     * string is simply returned as if by the <code>{@link #getPath}</code>
     * 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 Win32 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
     *
     * @see     java.io.File#isAbsolute()
     */
    public String getAbsolutePath() {
	return fs.resolve(this);
    }

    /**
     * Returns the absolute form of this abstract pathname.  Equivalent to
     * <code>new File(this.{@link #getAbsolutePath}())</code>.
     *
     * @return  The absolute abstract pathname denoting the same file or
     *          directory as this abstract pathname
     *
     * @since 1.2
     */
    public File getAbsoluteFile() {
	return new File(getAbsolutePath());
    }

    /**
     * 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 <tt>"."</tt> and <tt>".."</tt> from the pathname, resolving
     * symbolic links (on UNIX platforms), and converting drive letters to a
     * standard case (on Win32 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
     *
     * @since   JDK1.1
     */
    public String getCanonicalPath() throws IOException {
	return fs.canonicalize(fs.resolve(this));
    }

    /**
     * Returns the canonical form of this abstract pathname.  Equivalent to
     * <code>new 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
     *
     * @since 1.2
     */
    public File getCanonicalFile() throws IOException {
	return new File(getCanonicalPath());
    }

    /**
     * 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     java.net.URL
     * @since   1.2
     */
    public URL toURL() throws MalformedURLException {
	String path = getAbsolutePath();
        if (File.separatorChar != '/') {
            path = path.replace(File.separatorChar, '/');
        }
        if (!path.startsWith("/")) {
            path = "/" + path;
        }
        if (!path.endsWith("/") && isDirectory()) {
            path = path + "/";
        }
	return new URL("file", "", path);
    }


    /* -- Attribute accessors -- */

    /**
     * Tests whether the application can read the file denoted by this
     * abstract pathname.
     *
     * @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 <code>{@link
     *          java.lang.SecurityManager#checkRead}</code> method denies
     *          read access to the file
     */
    public boolean canRead() {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkRead(path);
	}
	return fs.checkAccess(this, false);
    }

    /**
     * Tests whether the application can modify to the file denoted by this
     * abstract pathname.
     *
     * @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 <code>{@link
     *          java.lang.SecurityManager#checkWrite}</code> method denies
     *          write access to the file
     */
    public boolean canWrite() {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkWrite(path);
	}
	return fs.checkAccess(this, true);
    }

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

    /**
     * Tests whether the file denoted by this abstract pathname is a
     * directory.
     *
     * @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 <code>{@link
     *          java.lang.SecurityManager#checkRead}</code> method denies
     *          read access to the file
     */
    public boolean isDirectory() {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkRead(path);
	}
	return ((fs.getBooleanAttributes(this) & FileSystem.BA_DIRECTORY)
		!= 0);
    }

    /**
     * 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.
     *
     * @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 <code>{@link
     *          java.lang.SecurityManager#checkRead}</code> method denies
     *          read access to the file
     */
    public boolean isFile() {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkRead(path);
	}
	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 <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 Win32 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 <code>{@link
     *          java.lang.SecurityManager#checkRead}</code> method denies
     *          read access to the file
     *
     * @since 1.2
     */
    public boolean isHidden() {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkRead(path);
	}
	return ((fs.getBooleanAttributes(this) & FileSystem.BA_HIDDEN) != 0);
    }

    /**
     * Returns the time that the file denoted by this abstract pathname was
     * last modified.
     *
     * @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
     *
     * @throws  SecurityException
     *          If a security manager exists and its <code>{@link
     *          java.lang.SecurityManager#checkRead}</code> method denies
     *          read access to the file
     */
    public long lastModified() {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkRead(path);
	}
	return fs.getLastModifiedTime(this);
    }

    /**
     * Returns the length of the file denoted by this abstract pathname.
     *
     * @return  The length, in bytes, of the file denoted by this abstract
     *          pathname, or <code>0L</code> if the file does not exist
     *
     * @throws  SecurityException
     *          If a security manager exists and its <code>{@link
     *          java.lang.SecurityManager#checkRead}</code> method denies
     *          read access to the file
     */
    public long length() {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkRead(path);
	}
	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.  This method, in
     * combination with the <code>{@link #deleteOnExit}</code> method, can
     * therefore serve as the basis for a simple but reliable cooperative
     * file-locking protocol.
     *
     * @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 <code>{@link
     *          java.lang.SecurityManager#checkWrite}</code> 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);
	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.
     *
     * @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 <code>{@link
     *          java.lang.SecurityManager#checkDelete}</code> method denies
     *          delete access to the file
     */
    public boolean delete() {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkDelete(path);
	}
	return fs.delete(this);
    }

    /**
     * Requests that the file or directory denoted by this abstract pathname
     * be deleted when the virtual machine terminates.  Deletion will be
     * attempted only for normal termination of the virtual machine, as defined
     * by the Java Language Specification (12.9).
     *
     * <p> Once deletion has been requested, it is not possible to cancel the
     * request.  This method should therefore be used with care.
     *
     * @throws  SecurityException
     *          If a security manager exists and its <code>{@link
     *          java.lang.SecurityManager#checkDelete}</code> 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);
	}
	fs.deleteOnExit(this);
    }

    /**
     * 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</code>.  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.
     *
     * @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</code> 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 <code>{@link
     *          java.lang.SecurityManager#checkRead}</code> method denies
     *          read access to the directory
     */
    public String[] list() {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkRead(path);
	}
	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
     * <code>{@link #list()}</code> method, except that the strings in the
     * returned array must satisfy the filter.  If the given
     * <code>filter</code> is <code>null</code> then all names are accepted.
     * Otherwise, a name satisfies the filter if and only if the value
     * <code>true</code> results when the <code>{@link
     * FilenameFilter#accept}</code> 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</code>.  The array will be empty if
     *          the directory is empty or if no names were accepted by the
     *          filter.  Returns <code>null</code> 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 <code>{@link
     *          java.lang.SecurityManager#checkRead}</code> method denies
     *          read access to the directory
     */
    public String[] list(FilenameFilter filter) {
	String names[] = list();
	if ((names == null) || (filter == null)) {
	    return names;
	}
	ArrayList v = new ArrayList();
	for (int i = 0 ; i < names.length ; i++) {
	    if (filter.accept(this, names[i])) {
		v.add(names[i]);
	    }
	}
	return (String[])(v.toArray(new String[0]));
    }

    /**
     * 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</code>.  Otherwise an array of
     * <code>File</code> 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 <code>{@link #File(java.io.File, java.lang.String)
     * File(File, String)}</code> 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.
     *
     * @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</code> 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 <code>{@link
     *          java.lang.SecurityManager#checkRead}</code> 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(this.path, ss[i]);
	}
	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 <code>{@link #listFiles()}</code> method, except
     * that the pathnames in the returned array must satisfy the filter.
     * If the given <code>filter</code> is <code>null</code> then all
     * pathnames are accepted.  Otherwise, a pathname satisfies the filter
     * if and only if the value <code>true</code> results when the
     * <code>{@link FilenameFilter#accept}</code> 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</code> 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 <code>{@link
     *          java.lang.SecurityManager#checkRead}</code> method denies
     *          read access to the directory
     *
     * @since 1.2
     */
    public File[] listFiles(FilenameFilter filter) {
	String ss[] = list();
	if (ss == null) return null;
	ArrayList v = new ArrayList();
	for (int i = 0 ; i < ss.length ; i++) {
	    if ((filter == null) || filter.accept(this, ss[i])) {
		v.add(new File(this.path, ss[i]));
	    }
	}
	return (File[])(v.toArray(new File[0]));
    }

    /**
     * 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 <code>{@link #listFiles()}</code> method, except
     * that the pathnames in the returned array must satisfy the filter.
     * If the given <code>filter</code> is <code>null</code> then all
     * pathnames are accepted.  Otherwise, a pathname satisfies the filter
     * if and only if the value <code>true</code> results when the
     * <code>{@link FilenameFilter#accept}</code> method of the filter is
     * invoked on the pathname.
     *
     * @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</code> 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 <code>{@link
     *          java.lang.SecurityManager#checkRead}</code> method denies
     *          read access to the directory
     *
     * @since 1.2
     */
    public File[] listFiles(FileFilter filter) {
	String ss[] = list();
	if (ss == null) return null;
	ArrayList v = new ArrayList();
	for (int i = 0 ; i < ss.length ; i++) {
	    File f = new File(this.path, ss[i]);
	    if ((filter == null) || filter.accept(f)) {
		v.add(f);
	    }
	}
	return (File[])(v.toArray(new File[0]));
    }

    /**
     * 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 <code>{@link
     *          java.lang.SecurityManager#checkWrite}</code> method does not
     *          permit the named directory to be created
     */
    public boolean mkdir() {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkWrite(path);
	}
	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.
     *
     * @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 <code>{@link
     *          java.lang.SecurityManager#checkWrite}</code> method does not
     *          permit the named directory and all necessary parent directories
     *          and to be created
     */
    public boolean mkdirs() {
	if (exists()) {
	    return false;
	}
	if (mkdir()) {
 	    return true;
 	}
	String parent = getParent();
	return (parent != null) && (new File(parent).mkdirs() && mkdir());
    }

    /**
     * Renames the file denoted by this abstract pathname.
     *
     * @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 <code>{@link
     *          java.lang.SecurityManager#checkWrite}</code> 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);
	}
	return fs.rename(this, dest);
    }

    /**
     * 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
     * <code>{@link #lastModified}</code> 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 <code>{@link
     *          java.lang.SecurityManager#checkWrite}</code> 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);
	}
	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 is guaranteed not to change until it is either deleted or
     * marked to allow write access.  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 <code>{@link
     *          java.lang.SecurityManager#checkWrite}</code> method denies
     *          write access to the named file
     *
     * @since 1.2
     */
    public boolean setReadOnly() {
	SecurityManager security = System.getSecurityManager();
	if (security != null) {
	    security.checkWrite(path);
	}
	return fs.setReadOnly(this);
    }


    /* -- Filesystem interface -- */

    /**
     * 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</code> 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>"/"</code>.  The set of available filesystem
     * roots is affected by various system-level operations such 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</code> 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</code> objects
     * denoting the root directories of the mapped network drives of a Windows
     * platform will be returned by this method, while <code>File</code>
     * 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 <code>{@link
     * java.lang.SecurityManager#checkRead}</code> method denies read access to
     * a particular root directory, then that directory will not appear in the
     * result.
     *
     * @return  An array of <code>File</code> objects denoting the available
     *          filesystem roots, or <code>null</code> if the set of roots
     *          could not be determined.  The array will be empty if there are
     *          no filesystem roots.
     *
     * @since 1.2
     */
    public static File[] listRoots() {
	return fs.listRoots();
    }


    /* -- Temporary files -- */

    private static final Object tmpFileLock = new Object();

    private static int counter = -1; /* Protected by tmpFileLock */

    private static File generateFile(String prefix, String suffix, File dir)
	throws IOException
    {
	if (counter == -1) {
	    counter = new Random().nextInt() & 0xffff;
	}
	counter++;
	return new File(dir, prefix + Integer.toString(counter) + suffix);
    }

    private static String tmpdir; /* Protected by tmpFileLock */

    private static String getTempDir() {
	if (tmpdir == null) {
	    GetPropertyAction a = new GetPropertyAction("java.io.tmpdir");
	    tmpdir = ((String) AccessController.doPrivileged(a));
	}
	return tmpdir;
    }

    private static boolean checkAndCreate(String filename, SecurityManager sm)
	throws IOException
    {
	if (sm != null) {
	    try {
		sm.checkWrite(filename);
	    } catch (AccessControlException x) {
		/* Throwing the original AccessControlException could disclose
		   the location of the default temporary directory, so we
		   re-throw a more innocuous SecurityException */
		throw new SecurityException("Unable to create temporary file");
	    }
	}
	return fs.createFileExclusively(filename);
    }

    /**
     * <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
     * <code>{@link #deleteOnExit}</code> 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
     * Win32 systems it is typically <code>"c:\\temp"</code>.
     *
     * @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 <code>{@link
     *          java.lang.SecurityManager#checkWrite}</code> 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 == null) throw new NullPointerException();
	if (prefix.length() < 3)
	    throw new IllegalArgumentException("Prefix string too short");
	String s = (suffix == null) ? ".tmp" : suffix;
	synchronized (tmpFileLock) {
	    if (directory == null) {
		directory = new File(getTempDir());
	    }
	    SecurityManager sm = System.getSecurityManager();
	    File f;
	    do {
		f = generateFile(prefix, s, directory);
	    } while (!checkAndCreate(f.getPath(), sm));
	    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 <code>{@link #createTempFile(java.lang.String,
     * java.lang.String, java.io.File)
     * createTempFile(prefix, suffix, null)}</code>.
     *
     * @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 <code>{@link
     *          java.lang.SecurityManager#checkWrite}</code> method does not
     *          allow a file to be created
     *
     * @since 1.2
     */
    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 Win32
     * 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);
    }

    /**
     * Compares this abstract pathname to another object.  If the other object
     * is an abstract pathname, then this function behaves like <code>{@link
     * #compareTo(File)}</code>.  Otherwise, it throws a
     * <code>ClassCastException</code>, since abstract pathnames can only be
     * compared to abstract pathnames.
     *
     * @param   o  The <code>Object</code> to be compared to this abstract
     *             pathname
     *
     * @return  If the argument is an 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
     *
     * @throws  <code>ClassCastException</code> if the argument is not an
     *		abstract pathname
     *
     * @see     java.lang.Comparable
     * @since   1.2
     */
    public int compareTo(Object o) {
	return compareTo((File)o);
    }

    /**
     * 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 Win32
     * 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 <em>or</em> of its pathname string
     * and the decimal value <code>1234321</code>.  On Win32 systems, the hash
     * code is equal to the exclusive <em>or</em> of its pathname string,
     * convered to lower case, and the decimal value <code>1234321</code>.
     *
     * @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 <code>{@link #getPath}</code> 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.
     */
    private synchronized void writeObject(java.io.ObjectOutputStream s)
        throws IOException
    {
	s.defaultWriteObject();
	s.writeChar(this.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 seperator
     * is replaced by the local separator.
     */
    private synchronized void readObject(java.io.ObjectInputStream s)
         throws IOException, ClassNotFoundException
    {
	s.defaultReadObject();
	char sep = s.readChar(); // read the previous seperator char
	if (sep != separatorChar)
	    this.path = this.path.replace(sep, separatorChar);
	this.path = fs.normalize(this.path);
	this.prefixLength = fs.prefixLength(this.path);
    }

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

}