1 /*
   2  * Copyright (c) 1994, 2019, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
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  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
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  23  * questions.
  24  */
  25 
  26 package java.io;
  27 
  28 import java.net.URI;
  29 import java.net.URL;
  30 import java.net.MalformedURLException;
  31 import java.net.URISyntaxException;
  32 import java.nio.file.FileSystems;
  33 import java.nio.file.Path;
  34 import java.security.SecureRandom;
  35 import java.util.ArrayList;
  36 import java.util.List;
  37 import sun.security.action.GetPropertyAction;
  38 
  39 /**
  40  * An abstract representation of file and directory pathnames.
  41  *
  42  * <p> User interfaces and operating systems use system-dependent <em>pathname
  43  * strings</em> to name files and directories.  This class presents an
  44  * abstract, system-independent view of hierarchical pathnames.  An
  45  * <em>abstract pathname</em> has two components:
  46  *
  47  * <ol>
  48  * <li> An optional system-dependent <em>prefix</em> string,
  49  *      such as a disk-drive specifier, <code>"/"</code>&nbsp;for the UNIX root
  50  *      directory, or <code>"\\\\"</code>&nbsp;for a Microsoft Windows UNC pathname, and
  51  * <li> A sequence of zero or more string <em>names</em>.
  52  * </ol>
  53  *
  54  * The first name in an abstract pathname may be a directory name or, in the
  55  * case of Microsoft Windows UNC pathnames, a hostname.  Each subsequent name
  56  * in an abstract pathname denotes a directory; the last name may denote
  57  * either a directory or a file.  The <em>empty</em> abstract pathname has no
  58  * prefix and an empty name sequence.
  59  *
  60  * <p> The conversion of a pathname string to or from an abstract pathname is
  61  * inherently system-dependent.  When an abstract pathname is converted into a
  62  * pathname string, each name is separated from the next by a single copy of
  63  * the default <em>separator character</em>.  The default name-separator
  64  * character is defined by the system property <code>file.separator</code>, and
  65  * is made available in the public static fields {@link
  66  * #separator} and {@link #separatorChar} of this class.
  67  * When a pathname string is converted into an abstract pathname, the names
  68  * within it may be separated by the default name-separator character or by any
  69  * other name-separator character that is supported by the underlying system.
  70  *
  71  * <p> A pathname, whether abstract or in string form, may be either
  72  * <em>absolute</em> or <em>relative</em>.  An absolute pathname is complete in
  73  * that no other information is required in order to locate the file that it
  74  * denotes.  A relative pathname, in contrast, must be interpreted in terms of
  75  * information taken from some other pathname.  By default the classes in the
  76  * <code>java.io</code> package always resolve relative pathnames against the
  77  * current user directory.  This directory is named by the system property
  78  * <code>user.dir</code>, and is typically the directory in which the Java
  79  * virtual machine was invoked.
  80  *
  81  * <p> The <em>parent</em> of an abstract pathname may be obtained by invoking
  82  * the {@link #getParent} method of this class and consists of the pathname's
  83  * prefix and each name in the pathname's name sequence except for the last.
  84  * Each directory's absolute pathname is an ancestor of any {@code File}
  85  * object with an absolute abstract pathname which begins with the directory's
  86  * absolute pathname.  For example, the directory denoted by the abstract
  87  * pathname {@code "/usr"} is an ancestor of the directory denoted by the
  88  * pathname {@code "/usr/local/bin"}.
  89  *
  90  * <p> The prefix concept is used to handle root directories on UNIX platforms,
  91  * and drive specifiers, root directories and UNC pathnames on Microsoft Windows platforms,
  92  * as follows:
  93  *
  94  * <ul>
  95  *
  96  * <li> For UNIX platforms, the prefix of an absolute pathname is always
  97  * <code>"/"</code>.  Relative pathnames have no prefix.  The abstract pathname
  98  * denoting the root directory has the prefix <code>"/"</code> and an empty
  99  * name sequence.
 100  *
 101  * <li> For Microsoft Windows platforms, the prefix of a pathname that contains a drive
 102  * specifier consists of the drive letter followed by <code>":"</code> and
 103  * possibly followed by <code>"\\"</code> if the pathname is absolute.  The
 104  * prefix of a UNC pathname is <code>"\\\\"</code>; the hostname and the share
 105  * name are the first two names in the name sequence.  A relative pathname that
 106  * does not specify a drive has no prefix.
 107  *
 108  * </ul>
 109  *
 110  * <p> Instances of this class may or may not denote an actual file-system
 111  * object such as a file or a directory.  If it does denote such an object
 112  * then that object resides in a <i>partition</i>.  A partition is an
 113  * operating system-specific portion of storage for a file system.  A single
 114  * storage device (e.g. a physical disk-drive, flash memory, CD-ROM) may
 115  * contain multiple partitions.  The object, if any, will reside on the
 116  * partition <a id="partName">named</a> by some ancestor of the absolute
 117  * form of this pathname.
 118  *
 119  * <p> A file system may implement restrictions to certain operations on the
 120  * actual file-system object, such as reading, writing, and executing.  These
 121  * restrictions are collectively known as <i>access permissions</i>.  The file
 122  * system may have multiple sets of access permissions on a single object.
 123  * For example, one set may apply to the object's <i>owner</i>, and another
 124  * may apply to all other users.  The access permissions on an object may
 125  * cause some methods in this class to fail.
 126  *
 127  * <p> Instances of the <code>File</code> class are immutable; that is, once
 128  * created, the abstract pathname represented by a <code>File</code> object
 129  * will never change.
 130  *
 131  * <h2>Interoperability with {@code java.nio.file} package</h2>
 132  *
 133  * <p> The <a href="../../java/nio/file/package-summary.html">{@code java.nio.file}</a>
 134  * package defines interfaces and classes for the Java virtual machine to access
 135  * files, file attributes, and file systems. This API may be used to overcome
 136  * many of the limitations of the {@code java.io.File} class.
 137  * The {@link #toPath toPath} method may be used to obtain a {@link
 138  * Path} that uses the abstract path represented by a {@code File} object to
 139  * locate a file. The resulting {@code Path} may be used with the {@link
 140  * java.nio.file.Files} class to provide more efficient and extensive access to
 141  * additional file operations, file attributes, and I/O exceptions to help
 142  * diagnose errors when an operation on a file fails.
 143  *
 144  * @author  unascribed
 145  * @since   1.0
 146  */
 147 
 148 public class File
 149     implements Serializable, Comparable<File>
 150 {
 151 
 152     /**
 153      * The FileSystem object representing the platform's local file system.
 154      */
 155     private static final FileSystem fs = DefaultFileSystem.getFileSystem();
 156 
 157     /**
 158      * This abstract pathname's normalized pathname string. A normalized
 159      * pathname string uses the default name-separator character and does not
 160      * contain any duplicate or redundant separators.
 161      *
 162      * @serial
 163      */
 164     private final String path;
 165 
 166     /**
 167      * Enum type that indicates the status of a file path.
 168      */
 169     private static enum PathStatus { INVALID, CHECKED };
 170 
 171     /**
 172      * The flag indicating whether the file path is invalid.
 173      */
 174     private transient PathStatus status = null;
 175 
 176     /**
 177      * Check if the file has an invalid path. Currently, the inspection of
 178      * a file path is very limited, and it only covers Nul character check.
 179      * Returning true means the path is definitely invalid/garbage. But
 180      * returning false does not guarantee that the path is valid.
 181      *
 182      * @return true if the file path is invalid.
 183      */
 184     final boolean isInvalid() {
 185         PathStatus s = status;
 186         if (s == null) {
 187             s = (this.path.indexOf('\u0000') < 0) ? PathStatus.CHECKED
 188                                                   : PathStatus.INVALID;
 189             status = s;
 190         }
 191         return s == PathStatus.INVALID;
 192     }
 193 
 194     /**
 195      * The length of this abstract pathname's prefix, or zero if it has no
 196      * prefix.
 197      */
 198     private final transient int prefixLength;
 199 
 200     /**
 201      * Returns the length of this abstract pathname's prefix.
 202      * For use by FileSystem classes.
 203      */
 204     int getPrefixLength() {
 205         return prefixLength;
 206     }
 207 
 208     /**
 209      * The system-dependent default name-separator character.  This field is
 210      * initialized to contain the first character of the value of the system
 211      * property <code>file.separator</code>.  On UNIX systems the value of this
 212      * field is <code>'/'</code>; on Microsoft Windows systems it is <code>'\\'</code>.
 213      *
 214      * @see     java.lang.System#getProperty(java.lang.String)
 215      */
 216     public static final char separatorChar = fs.getSeparator();
 217 
 218     /**
 219      * The system-dependent default name-separator character, represented as a
 220      * string for convenience.  This string contains a single character, namely
 221      * {@link #separatorChar}.
 222      */
 223     public static final String separator = "" + separatorChar;
 224 
 225     /**
 226      * The system-dependent path-separator character.  This field is
 227      * initialized to contain the first character of the value of the system
 228      * property <code>path.separator</code>.  This character is used to
 229      * separate filenames in a sequence of files given as a <em>path list</em>.
 230      * On UNIX systems, this character is <code>':'</code>; on Microsoft Windows systems it
 231      * is <code>';'</code>.
 232      *
 233      * @see     java.lang.System#getProperty(java.lang.String)
 234      */
 235     public static final char pathSeparatorChar = fs.getPathSeparator();
 236 
 237     /**
 238      * The system-dependent path-separator character, represented as a string
 239      * for convenience.  This string contains a single character, namely
 240      * {@link #pathSeparatorChar}.
 241      */
 242     public static final String pathSeparator = "" + pathSeparatorChar;
 243 
 244 
 245     /* -- Constructors -- */
 246 
 247     /**
 248      * Internal constructor for already-normalized pathname strings.
 249      */
 250     private File(String pathname, int prefixLength) {
 251         this.path = pathname;
 252         this.prefixLength = prefixLength;
 253     }
 254 
 255     /**
 256      * Internal constructor for already-normalized pathname strings.
 257      * The parameter order is used to disambiguate this method from the
 258      * public(File, String) constructor.
 259      */
 260     private File(String child, File parent) {
 261         assert parent.path != null;
 262         assert (!parent.path.isEmpty());
 263         this.path = fs.resolve(parent.path, child);
 264         this.prefixLength = parent.prefixLength;
 265     }
 266 
 267     /**
 268      * Creates a new <code>File</code> instance by converting the given
 269      * pathname string into an abstract pathname.  If the given string is
 270      * the empty string, then the result is the empty abstract pathname.
 271      *
 272      * @param   pathname  A pathname string
 273      * @throws  NullPointerException
 274      *          If the <code>pathname</code> argument is <code>null</code>
 275      */
 276     public File(String pathname) {
 277         if (pathname == null) {
 278             throw new NullPointerException();
 279         }
 280         this.path = fs.normalize(pathname);
 281         this.prefixLength = fs.prefixLength(this.path);
 282     }
 283 
 284     /* Note: The two-argument File constructors do not interpret an empty
 285        parent abstract pathname as the current user directory.  An empty parent
 286        instead causes the child to be resolved against the system-dependent
 287        directory defined by the FileSystem.getDefaultParent method.  On Unix
 288        this default is "/", while on Microsoft Windows it is "\\".  This is required for
 289        compatibility with the original behavior of this class. */
 290 
 291     /**
 292      * Creates a new <code>File</code> instance from a parent pathname string
 293      * and a child pathname string.
 294      *
 295      * <p> If <code>parent</code> is <code>null</code> then the new
 296      * <code>File</code> instance is created as if by invoking the
 297      * single-argument <code>File</code> constructor on the given
 298      * <code>child</code> pathname string.
 299      *
 300      * <p> Otherwise the <code>parent</code> pathname string is taken to denote
 301      * a directory, and the <code>child</code> pathname string is taken to
 302      * denote either a directory or a file.  If the <code>child</code> pathname
 303      * string is absolute then it is converted into a relative pathname in a
 304      * system-dependent way.  If <code>parent</code> is the empty string then
 305      * the new <code>File</code> instance is created by converting
 306      * <code>child</code> into an abstract pathname and resolving the result
 307      * against a system-dependent default directory.  Otherwise each pathname
 308      * string is converted into an abstract pathname and the child abstract
 309      * pathname is resolved against the parent.
 310      *
 311      * @param   parent  The parent pathname string
 312      * @param   child   The child pathname string
 313      * @throws  NullPointerException
 314      *          If <code>child</code> is <code>null</code>
 315      */
 316     public File(String parent, String child) {
 317         if (child == null) {
 318             throw new NullPointerException();
 319         }
 320         if (parent != null) {
 321             if (parent.isEmpty()) {
 322                 this.path = fs.resolve(fs.getDefaultParent(),
 323                                        fs.normalize(child));
 324             } else {
 325                 this.path = fs.resolve(fs.normalize(parent),
 326                                        fs.normalize(child));
 327             }
 328         } else {
 329             this.path = fs.normalize(child);
 330         }
 331         this.prefixLength = fs.prefixLength(this.path);
 332     }
 333 
 334     /**
 335      * Creates a new <code>File</code> instance from a parent abstract
 336      * pathname and a child pathname string.
 337      *
 338      * <p> If <code>parent</code> is <code>null</code> then the new
 339      * <code>File</code> instance is created as if by invoking the
 340      * single-argument <code>File</code> constructor on the given
 341      * <code>child</code> pathname string.
 342      *
 343      * <p> Otherwise the <code>parent</code> abstract pathname is taken to
 344      * denote a directory, and the <code>child</code> pathname string is taken
 345      * to denote either a directory or a file.  If the <code>child</code>
 346      * pathname string is absolute then it is converted into a relative
 347      * pathname in a system-dependent way.  If <code>parent</code> is the empty
 348      * abstract pathname then the new <code>File</code> instance is created by
 349      * converting <code>child</code> into an abstract pathname and resolving
 350      * the result against a system-dependent default directory.  Otherwise each
 351      * pathname string is converted into an abstract pathname and the child
 352      * abstract pathname is resolved against the parent.
 353      *
 354      * @param   parent  The parent abstract pathname
 355      * @param   child   The child pathname string
 356      * @throws  NullPointerException
 357      *          If <code>child</code> is <code>null</code>
 358      */
 359     public File(File parent, String child) {
 360         if (child == null) {
 361             throw new NullPointerException();
 362         }
 363         if (parent != null) {
 364             if (parent.path.isEmpty()) {
 365                 this.path = fs.resolve(fs.getDefaultParent(),
 366                                        fs.normalize(child));
 367             } else {
 368                 this.path = fs.resolve(parent.path,
 369                                        fs.normalize(child));
 370             }
 371         } else {
 372             this.path = fs.normalize(child);
 373         }
 374         this.prefixLength = fs.prefixLength(this.path);
 375     }
 376 
 377     /**
 378      * Creates a new {@code File} instance by converting the given
 379      * {@code file:} URI into an abstract pathname.
 380      *
 381      * <p> The exact form of a {@code file:} URI is system-dependent, hence
 382      * the transformation performed by this constructor is also
 383      * system-dependent.
 384      *
 385      * <p> For a given abstract pathname <i>f</i> it is guaranteed that
 386      *
 387      * <blockquote><code>
 388      * new File(</code><i>&nbsp;f</i><code>.{@link #toURI()
 389      * toURI}()).equals(</code><i>&nbsp;f</i><code>.{@link #getAbsoluteFile() getAbsoluteFile}())
 390      * </code></blockquote>
 391      *
 392      * so long as the original abstract pathname, the URI, and the new abstract
 393      * pathname are all created in (possibly different invocations of) the same
 394      * Java virtual machine.  This relationship typically does not hold,
 395      * however, when a {@code file:} URI that is created in a virtual machine
 396      * on one operating system is converted into an abstract pathname in a
 397      * virtual machine on a different operating system.
 398      *
 399      * @param  uri
 400      *         An absolute, hierarchical URI with a scheme equal to
 401      *         {@code "file"}, a non-empty path component, and undefined
 402      *         authority, query, and fragment components
 403      *
 404      * @throws  NullPointerException
 405      *          If {@code uri} is {@code null}
 406      *
 407      * @throws  IllegalArgumentException
 408      *          If the preconditions on the parameter do not hold
 409      *
 410      * @see #toURI()
 411      * @see java.net.URI
 412      * @since 1.4
 413      */
 414     public File(URI uri) {
 415 
 416         // Check our many preconditions
 417         if (!uri.isAbsolute())
 418             throw new IllegalArgumentException("URI is not absolute");
 419         if (uri.isOpaque())
 420             throw new IllegalArgumentException("URI is not hierarchical");
 421         String scheme = uri.getScheme();
 422         if ((scheme == null) || !scheme.equalsIgnoreCase("file"))
 423             throw new IllegalArgumentException("URI scheme is not \"file\"");
 424         if (uri.getRawAuthority() != null)
 425             throw new IllegalArgumentException("URI has an authority component");
 426         if (uri.getRawFragment() != null)
 427             throw new IllegalArgumentException("URI has a fragment component");
 428         if (uri.getRawQuery() != null)
 429             throw new IllegalArgumentException("URI has a query component");
 430         String p = uri.getPath();
 431         if (p.isEmpty())
 432             throw new IllegalArgumentException("URI path component is empty");
 433 
 434         // Okay, now initialize
 435         p = fs.fromURIPath(p);
 436         if (File.separatorChar != '/')
 437             p = p.replace('/', File.separatorChar);
 438         this.path = fs.normalize(p);
 439         this.prefixLength = fs.prefixLength(this.path);
 440     }
 441 
 442 
 443     /* -- Path-component accessors -- */
 444 
 445     /**
 446      * Returns the name of the file or directory denoted by this abstract
 447      * pathname.  This is just the last name in the pathname's name
 448      * sequence.  If the pathname's name sequence is empty, then the empty
 449      * string is returned.
 450      *
 451      * @return  The name of the file or directory denoted by this abstract
 452      *          pathname, or the empty string if this pathname's name sequence
 453      *          is empty
 454      */
 455     public String getName() {
 456         int index = path.lastIndexOf(separatorChar);
 457         if (index < prefixLength) return path.substring(prefixLength);
 458         return path.substring(index + 1);
 459     }
 460 
 461     /**
 462      * Returns the pathname string of this abstract pathname's parent, or
 463      * <code>null</code> if this pathname does not name a parent directory.
 464      *
 465      * <p> The <em>parent</em> of an abstract pathname consists of the
 466      * pathname's prefix, if any, and each name in the pathname's name
 467      * sequence except for the last.  If the name sequence is empty then
 468      * the pathname does not name a parent directory.
 469      *
 470      * @return  The pathname string of the parent directory named by this
 471      *          abstract pathname, or <code>null</code> if this pathname
 472      *          does not name a parent
 473      */
 474     public String getParent() {
 475         int index = path.lastIndexOf(separatorChar);
 476         if (index < prefixLength) {
 477             if ((prefixLength > 0) && (path.length() > prefixLength))
 478                 return path.substring(0, prefixLength);
 479             return null;
 480         }
 481         return path.substring(0, index);
 482     }
 483 
 484     /**
 485      * Returns the abstract pathname of this abstract pathname's parent,
 486      * or <code>null</code> if this pathname does not name a parent
 487      * directory.
 488      *
 489      * <p> The <em>parent</em> of an abstract pathname consists of the
 490      * pathname's prefix, if any, and each name in the pathname's name
 491      * sequence except for the last.  If the name sequence is empty then
 492      * the pathname does not name a parent directory.
 493      *
 494      * @return  The abstract pathname of the parent directory named by this
 495      *          abstract pathname, or <code>null</code> if this pathname
 496      *          does not name a parent
 497      *
 498      * @since 1.2
 499      */
 500     public File getParentFile() {
 501         String p = this.getParent();
 502         if (p == null) return null;
 503         return new File(p, this.prefixLength);
 504     }
 505 
 506     /**
 507      * Converts this abstract pathname into a pathname string.  The resulting
 508      * string uses the {@link #separator default name-separator character} to
 509      * separate the names in the name sequence.
 510      *
 511      * @return  The string form of this abstract pathname
 512      */
 513     public String getPath() {
 514         return path;
 515     }
 516 
 517 
 518     /* -- Path operations -- */
 519 
 520     /**
 521      * Tests whether this abstract pathname is absolute.  The definition of
 522      * absolute pathname is system dependent.  On UNIX systems, a pathname is
 523      * absolute if its prefix is <code>"/"</code>.  On Microsoft Windows systems, a
 524      * pathname is absolute if its prefix is a drive specifier followed by
 525      * <code>"\\"</code>, or if its prefix is <code>"\\\\"</code>.
 526      *
 527      * @return  <code>true</code> if this abstract pathname is absolute,
 528      *          <code>false</code> otherwise
 529      */
 530     public boolean isAbsolute() {
 531         return fs.isAbsolute(this);
 532     }
 533 
 534     /**
 535      * Returns the absolute pathname string of this abstract pathname.
 536      *
 537      * <p> If this abstract pathname is already absolute, then the pathname
 538      * string is simply returned as if by the {@link #getPath}
 539      * method.  If this abstract pathname is the empty abstract pathname then
 540      * the pathname string of the current user directory, which is named by the
 541      * system property <code>user.dir</code>, is returned.  Otherwise this
 542      * pathname is resolved in a system-dependent way.  On UNIX systems, a
 543      * relative pathname is made absolute by resolving it against the current
 544      * user directory.  On Microsoft Windows systems, a relative pathname is made absolute
 545      * by resolving it against the current directory of the drive named by the
 546      * pathname, if any; if not, it is resolved against the current user
 547      * directory.
 548      *
 549      * @return  The absolute pathname string denoting the same file or
 550      *          directory as this abstract pathname
 551      *
 552      * @throws  SecurityException
 553      *          If a required system property value cannot be accessed.
 554      *
 555      * @see     java.io.File#isAbsolute()
 556      */
 557     public String getAbsolutePath() {
 558         return fs.resolve(this);
 559     }
 560 
 561     /**
 562      * Returns the absolute form of this abstract pathname.  Equivalent to
 563      * <code>new&nbsp;File(this.{@link #getAbsolutePath})</code>.
 564      *
 565      * @return  The absolute abstract pathname denoting the same file or
 566      *          directory as this abstract pathname
 567      *
 568      * @throws  SecurityException
 569      *          If a required system property value cannot be accessed.
 570      *
 571      * @since 1.2
 572      */
 573     public File getAbsoluteFile() {
 574         String absPath = getAbsolutePath();
 575         return new File(absPath, fs.prefixLength(absPath));
 576     }
 577 
 578     /**
 579      * Returns the canonical pathname string of this abstract pathname.
 580      *
 581      * <p> A canonical pathname is both absolute and unique.  The precise
 582      * definition of canonical form is system-dependent.  This method first
 583      * converts this pathname to absolute form if necessary, as if by invoking the
 584      * {@link #getAbsolutePath} method, and then maps it to its unique form in a
 585      * system-dependent way.  This typically involves removing redundant names
 586      * such as {@code "."} and {@code ".."} from the pathname, resolving
 587      * symbolic links (on UNIX platforms), and converting drive letters to a
 588      * standard case (on Microsoft Windows platforms).
 589      *
 590      * <p> Every pathname that denotes an existing file or directory has a
 591      * unique canonical form.  Every pathname that denotes a nonexistent file
 592      * or directory also has a unique canonical form.  The canonical form of
 593      * the pathname of a nonexistent file or directory may be different from
 594      * the canonical form of the same pathname after the file or directory is
 595      * created.  Similarly, the canonical form of the pathname of an existing
 596      * file or directory may be different from the canonical form of the same
 597      * pathname after the file or directory is deleted.
 598      *
 599      * @return  The canonical pathname string denoting the same file or
 600      *          directory as this abstract pathname
 601      *
 602      * @throws  IOException
 603      *          If an I/O error occurs, which is possible because the
 604      *          construction of the canonical pathname may require
 605      *          filesystem queries
 606      *
 607      * @throws  SecurityException
 608      *          If a required system property value cannot be accessed, or
 609      *          if a security manager exists and its {@link
 610      *          java.lang.SecurityManager#checkRead} method denies
 611      *          read access to the file
 612      *
 613      * @since   1.1
 614      * @see     Path#toRealPath
 615      */
 616     public String getCanonicalPath() throws IOException {
 617         if (isInvalid()) {
 618             throw new IOException("Invalid file path");
 619         }
 620         return fs.canonicalize(fs.resolve(this));
 621     }
 622 
 623     /**
 624      * Returns the canonical form of this abstract pathname.  Equivalent to
 625      * <code>new&nbsp;File(this.{@link #getCanonicalPath})</code>.
 626      *
 627      * @return  The canonical pathname string denoting the same file or
 628      *          directory as this abstract pathname
 629      *
 630      * @throws  IOException
 631      *          If an I/O error occurs, which is possible because the
 632      *          construction of the canonical pathname may require
 633      *          filesystem queries
 634      *
 635      * @throws  SecurityException
 636      *          If a required system property value cannot be accessed, or
 637      *          if a security manager exists and its {@link
 638      *          java.lang.SecurityManager#checkRead} method denies
 639      *          read access to the file
 640      *
 641      * @since 1.2
 642      * @see     Path#toRealPath
 643      */
 644     public File getCanonicalFile() throws IOException {
 645         String canonPath = getCanonicalPath();
 646         return new File(canonPath, fs.prefixLength(canonPath));
 647     }
 648 
 649     private static String slashify(String path, boolean isDirectory) {
 650         String p = path;
 651         if (File.separatorChar != '/')
 652             p = p.replace(File.separatorChar, '/');
 653         if (!p.startsWith("/"))
 654             p = "/" + p;
 655         if (!p.endsWith("/") && isDirectory)
 656             p = p + "/";
 657         return p;
 658     }
 659 
 660     /**
 661      * Converts this abstract pathname into a <code>file:</code> URL.  The
 662      * exact form of the URL is system-dependent.  If it can be determined that
 663      * the file denoted by this abstract pathname is a directory, then the
 664      * resulting URL will end with a slash.
 665      *
 666      * @return  A URL object representing the equivalent file URL
 667      *
 668      * @throws  MalformedURLException
 669      *          If the path cannot be parsed as a URL
 670      *
 671      * @see     #toURI()
 672      * @see     java.net.URI
 673      * @see     java.net.URI#toURL()
 674      * @see     java.net.URL
 675      * @since   1.2
 676      *
 677      * @deprecated This method does not automatically escape characters that
 678      * are illegal in URLs.  It is recommended that new code convert an
 679      * abstract pathname into a URL by first converting it into a URI, via the
 680      * {@link #toURI() toURI} method, and then converting the URI into a URL
 681      * via the {@link java.net.URI#toURL() URI.toURL} method.
 682      */
 683     @Deprecated
 684     public URL toURL() throws MalformedURLException {
 685         if (isInvalid()) {
 686             throw new MalformedURLException("Invalid file path");
 687         }
 688         return new URL("file", "", slashify(getAbsolutePath(), isDirectory()));
 689     }
 690 
 691     /**
 692      * Constructs a {@code file:} URI that represents this abstract pathname.
 693      *
 694      * <p> The exact form of the URI is system-dependent.  If it can be
 695      * determined that the file denoted by this abstract pathname is a
 696      * directory, then the resulting URI will end with a slash.
 697      *
 698      * <p> For a given abstract pathname <i>f</i>, it is guaranteed that
 699      *
 700      * <blockquote><code>
 701      * new {@link #File(java.net.URI) File}(</code><i>&nbsp;f</i><code>.toURI()).equals(
 702      * </code><i>&nbsp;f</i><code>.{@link #getAbsoluteFile() getAbsoluteFile}())
 703      * </code></blockquote>
 704      *
 705      * so long as the original abstract pathname, the URI, and the new abstract
 706      * pathname are all created in (possibly different invocations of) the same
 707      * Java virtual machine.  Due to the system-dependent nature of abstract
 708      * pathnames, however, this relationship typically does not hold when a
 709      * {@code file:} URI that is created in a virtual machine on one operating
 710      * system is converted into an abstract pathname in a virtual machine on a
 711      * different operating system.
 712      *
 713      * <p> Note that when this abstract pathname represents a UNC pathname then
 714      * all components of the UNC (including the server name component) are encoded
 715      * in the {@code URI} path. The authority component is undefined, meaning
 716      * that it is represented as {@code null}. The {@link Path} class defines the
 717      * {@link Path#toUri toUri} method to encode the server name in the authority
 718      * component of the resulting {@code URI}. The {@link #toPath toPath} method
 719      * may be used to obtain a {@code Path} representing this abstract pathname.
 720      *
 721      * @return  An absolute, hierarchical URI with a scheme equal to
 722      *          {@code "file"}, a path representing this abstract pathname,
 723      *          and undefined authority, query, and fragment components
 724      * @throws SecurityException If a required system property value cannot
 725      * be accessed.
 726      *
 727      * @see #File(java.net.URI)
 728      * @see java.net.URI
 729      * @see java.net.URI#toURL()
 730      * @since 1.4
 731      */
 732     public URI toURI() {
 733         try {
 734             File f = getAbsoluteFile();
 735             String sp = slashify(f.getPath(), f.isDirectory());
 736             if (sp.startsWith("//"))
 737                 sp = "//" + sp;
 738             return new URI("file", null, sp, null);
 739         } catch (URISyntaxException x) {
 740             throw new Error(x);         // Can't happen
 741         }
 742     }
 743 
 744 
 745     /* -- Attribute accessors -- */
 746 
 747     /**
 748      * Tests whether the application can read the file denoted by this
 749      * abstract pathname. On some platforms it may be possible to start the
 750      * Java virtual machine with special privileges that allow it to read
 751      * files that are marked as unreadable. Consequently this method may return
 752      * {@code true} even though the file does not have read permissions.
 753      *
 754      * @return  <code>true</code> if and only if the file specified by this
 755      *          abstract pathname exists <em>and</em> can be read by the
 756      *          application; <code>false</code> otherwise
 757      *
 758      * @throws  SecurityException
 759      *          If a security manager exists and its {@link
 760      *          java.lang.SecurityManager#checkRead(java.lang.String)}
 761      *          method denies read access to the file
 762      */
 763     public boolean canRead() {
 764         SecurityManager security = System.getSecurityManager();
 765         if (security != null) {
 766             security.checkRead(path);
 767         }
 768         if (isInvalid()) {
 769             return false;
 770         }
 771         return fs.checkAccess(this, FileSystem.ACCESS_READ);
 772     }
 773 
 774     /**
 775      * Tests whether the application can modify the file denoted by this
 776      * abstract pathname. On some platforms it may be possible to start the
 777      * Java virtual machine with special privileges that allow it to modify
 778      * files that are marked read-only. Consequently this method may return
 779      * {@code true} even though the file is marked read-only.
 780      *
 781      * @return  <code>true</code> if and only if the file system actually
 782      *          contains a file denoted by this abstract pathname <em>and</em>
 783      *          the application is allowed to write to the file;
 784      *          <code>false</code> otherwise.
 785      *
 786      * @throws  SecurityException
 787      *          If a security manager exists and its {@link
 788      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
 789      *          method denies write access to the file
 790      */
 791     public boolean canWrite() {
 792         SecurityManager security = System.getSecurityManager();
 793         if (security != null) {
 794             security.checkWrite(path);
 795         }
 796         if (isInvalid()) {
 797             return false;
 798         }
 799         return fs.checkAccess(this, FileSystem.ACCESS_WRITE);
 800     }
 801 
 802     /**
 803      * Tests whether the file or directory denoted by this abstract pathname
 804      * exists.
 805      *
 806      * @return  <code>true</code> if and only if the file or directory denoted
 807      *          by this abstract pathname exists; <code>false</code> otherwise
 808      *
 809      * @throws  SecurityException
 810      *          If a security manager exists and its {@link
 811      *          java.lang.SecurityManager#checkRead(java.lang.String)}
 812      *          method denies read access to the file or directory
 813      */
 814     public boolean exists() {
 815         SecurityManager security = System.getSecurityManager();
 816         if (security != null) {
 817             security.checkRead(path);
 818         }
 819         if (isInvalid()) {
 820             return false;
 821         }
 822         return ((fs.getBooleanAttributes(this) & FileSystem.BA_EXISTS) != 0);
 823     }
 824 
 825     /**
 826      * Tests whether the file denoted by this abstract pathname is a
 827      * directory.
 828      *
 829      * <p> Where it is required to distinguish an I/O exception from the case
 830      * that the file is not a directory, or where several attributes of the
 831      * same file are required at the same time, then the {@link
 832      * java.nio.file.Files#readAttributes(Path,Class,LinkOption[])
 833      * Files.readAttributes} method may be used.
 834      *
 835      * @return <code>true</code> if and only if the file denoted by this
 836      *          abstract pathname exists <em>and</em> is a directory;
 837      *          <code>false</code> otherwise
 838      *
 839      * @throws  SecurityException
 840      *          If a security manager exists and its {@link
 841      *          java.lang.SecurityManager#checkRead(java.lang.String)}
 842      *          method denies read access to the file
 843      */
 844     public boolean isDirectory() {
 845         SecurityManager security = System.getSecurityManager();
 846         if (security != null) {
 847             security.checkRead(path);
 848         }
 849         if (isInvalid()) {
 850             return false;
 851         }
 852         return ((fs.getBooleanAttributes(this) & FileSystem.BA_DIRECTORY)
 853                 != 0);
 854     }
 855 
 856     /**
 857      * Tests whether the file denoted by this abstract pathname is a normal
 858      * file.  A file is <em>normal</em> if it is not a directory and, in
 859      * addition, satisfies other system-dependent criteria.  Any non-directory
 860      * file created by a Java application is guaranteed to be a normal file.
 861      *
 862      * <p> Where it is required to distinguish an I/O exception from the case
 863      * that the file is not a normal file, or where several attributes of the
 864      * same file are required at the same time, then the {@link
 865      * java.nio.file.Files#readAttributes(Path,Class,LinkOption[])
 866      * Files.readAttributes} method may be used.
 867      *
 868      * @return  <code>true</code> if and only if the file denoted by this
 869      *          abstract pathname exists <em>and</em> is a normal file;
 870      *          <code>false</code> otherwise
 871      *
 872      * @throws  SecurityException
 873      *          If a security manager exists and its {@link
 874      *          java.lang.SecurityManager#checkRead(java.lang.String)}
 875      *          method denies read access to the file
 876      */
 877     public boolean isFile() {
 878         SecurityManager security = System.getSecurityManager();
 879         if (security != null) {
 880             security.checkRead(path);
 881         }
 882         if (isInvalid()) {
 883             return false;
 884         }
 885         return ((fs.getBooleanAttributes(this) & FileSystem.BA_REGULAR) != 0);
 886     }
 887 
 888     /**
 889      * Tests whether the file named by this abstract pathname is a hidden
 890      * file.  The exact definition of <em>hidden</em> is system-dependent.  On
 891      * UNIX systems, a file is considered to be hidden if its name begins with
 892      * a period character (<code>'.'</code>).  On Microsoft Windows systems, a file is
 893      * considered to be hidden if it has been marked as such in the filesystem.
 894      *
 895      * @return  <code>true</code> if and only if the file denoted by this
 896      *          abstract pathname is hidden according to the conventions of the
 897      *          underlying platform
 898      *
 899      * @throws  SecurityException
 900      *          If a security manager exists and its {@link
 901      *          java.lang.SecurityManager#checkRead(java.lang.String)}
 902      *          method denies read access to the file
 903      *
 904      * @since 1.2
 905      */
 906     public boolean isHidden() {
 907         SecurityManager security = System.getSecurityManager();
 908         if (security != null) {
 909             security.checkRead(path);
 910         }
 911         if (isInvalid()) {
 912             return false;
 913         }
 914         return ((fs.getBooleanAttributes(this) & FileSystem.BA_HIDDEN) != 0);
 915     }
 916 
 917     /**
 918      * Returns the time that the file denoted by this abstract pathname was
 919      * last modified.
 920      *
 921      * @apiNote
 922      * While the unit of time of the return value is milliseconds, the
 923      * granularity of the value depends on the underlying file system and may
 924      * be larger.  For example, some file systems use time stamps in units of
 925      * seconds.
 926      *
 927      * <p> Where it is required to distinguish an I/O exception from the case
 928      * where {@code 0L} is returned, or where several attributes of the
 929      * same file are required at the same time, or where the time of last
 930      * access or the creation time are required, then the {@link
 931      * java.nio.file.Files#readAttributes(Path,Class,LinkOption[])
 932      * Files.readAttributes} method may be used.  If however only the
 933      * time of last modification is required, then the
 934      * {@link java.nio.file.Files#getLastModifiedTime(Path,LinkOption[])
 935      * Files.getLastModifiedTime} method may be used instead.
 936      *
 937      * @return  A <code>long</code> value representing the time the file was
 938      *          last modified, measured in milliseconds since the epoch
 939      *          (00:00:00 GMT, January 1, 1970), or <code>0L</code> if the
 940      *          file does not exist or if an I/O error occurs.  The value may
 941      *          be negative indicating the number of milliseconds before the
 942      *          epoch
 943      *
 944      * @throws  SecurityException
 945      *          If a security manager exists and its {@link
 946      *          java.lang.SecurityManager#checkRead(java.lang.String)}
 947      *          method denies read access to the file
 948      */
 949     public long lastModified() {
 950         SecurityManager security = System.getSecurityManager();
 951         if (security != null) {
 952             security.checkRead(path);
 953         }
 954         if (isInvalid()) {
 955             return 0L;
 956         }
 957         return fs.getLastModifiedTime(this);
 958     }
 959 
 960     /**
 961      * Returns the length of the file denoted by this abstract pathname.
 962      * The return value is unspecified if this pathname denotes a directory.
 963      *
 964      * <p> Where it is required to distinguish an I/O exception from the case
 965      * that {@code 0L} is returned, or where several attributes of the same file
 966      * are required at the same time, then the {@link
 967      * java.nio.file.Files#readAttributes(Path,Class,LinkOption[])
 968      * Files.readAttributes} method may be used.
 969      *
 970      * @return  The length, in bytes, of the file denoted by this abstract
 971      *          pathname, or <code>0L</code> if the file does not exist.  Some
 972      *          operating systems may return <code>0L</code> for pathnames
 973      *          denoting system-dependent entities such as devices or pipes.
 974      *
 975      * @throws  SecurityException
 976      *          If a security manager exists and its {@link
 977      *          java.lang.SecurityManager#checkRead(java.lang.String)}
 978      *          method denies read access to the file
 979      */
 980     public long length() {
 981         SecurityManager security = System.getSecurityManager();
 982         if (security != null) {
 983             security.checkRead(path);
 984         }
 985         if (isInvalid()) {
 986             return 0L;
 987         }
 988         return fs.getLength(this);
 989     }
 990 
 991 
 992     /* -- File operations -- */
 993 
 994     /**
 995      * Atomically creates a new, empty file named by this abstract pathname if
 996      * and only if a file with this name does not yet exist.  The check for the
 997      * existence of the file and the creation of the file if it does not exist
 998      * are a single operation that is atomic with respect to all other
 999      * filesystem activities that might affect the file.
1000      * <P>
1001      * Note: this method should <i>not</i> be used for file-locking, as
1002      * the resulting protocol cannot be made to work reliably. The
1003      * {@link java.nio.channels.FileLock FileLock}
1004      * facility should be used instead.
1005      *
1006      * @return  <code>true</code> if the named file does not exist and was
1007      *          successfully created; <code>false</code> if the named file
1008      *          already exists
1009      *
1010      * @throws  IOException
1011      *          If an I/O error occurred
1012      *
1013      * @throws  SecurityException
1014      *          If a security manager exists and its {@link
1015      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1016      *          method denies write access to the file
1017      *
1018      * @since 1.2
1019      */
1020     public boolean createNewFile() throws IOException {
1021         SecurityManager security = System.getSecurityManager();
1022         if (security != null) security.checkWrite(path);
1023         if (isInvalid()) {
1024             throw new IOException("Invalid file path");
1025         }
1026         return fs.createFileExclusively(path);
1027     }
1028 
1029     /**
1030      * Deletes the file or directory denoted by this abstract pathname.  If
1031      * this pathname denotes a directory, then the directory must be empty in
1032      * order to be deleted.
1033      *
1034      * <p> Note that the {@link java.nio.file.Files} class defines the {@link
1035      * java.nio.file.Files#delete(Path) delete} method to throw an {@link IOException}
1036      * when a file cannot be deleted. This is useful for error reporting and to
1037      * diagnose why a file cannot be deleted.
1038      *
1039      * @return  <code>true</code> if and only if the file or directory is
1040      *          successfully deleted; <code>false</code> otherwise
1041      *
1042      * @throws  SecurityException
1043      *          If a security manager exists and its {@link
1044      *          java.lang.SecurityManager#checkDelete} method denies
1045      *          delete access to the file
1046      */
1047     public boolean delete() {
1048         SecurityManager security = System.getSecurityManager();
1049         if (security != null) {
1050             security.checkDelete(path);
1051         }
1052         if (isInvalid()) {
1053             return false;
1054         }
1055         return fs.delete(this);
1056     }
1057 
1058     /**
1059      * Requests that the file or directory denoted by this abstract
1060      * pathname be deleted when the virtual machine terminates.
1061      * Files (or directories) are deleted in the reverse order that
1062      * they are registered. Invoking this method to delete a file or
1063      * directory that is already registered for deletion has no effect.
1064      * Deletion will be attempted only for normal termination of the
1065      * virtual machine, as defined by the Java Language Specification.
1066      *
1067      * <p> Once deletion has been requested, it is not possible to cancel the
1068      * request.  This method should therefore be used with care.
1069      *
1070      * <P>
1071      * Note: this method should <i>not</i> be used for file-locking, as
1072      * the resulting protocol cannot be made to work reliably. The
1073      * {@link java.nio.channels.FileLock FileLock}
1074      * facility should be used instead.
1075      *
1076      * @throws  SecurityException
1077      *          If a security manager exists and its {@link
1078      *          java.lang.SecurityManager#checkDelete} method denies
1079      *          delete access to the file
1080      *
1081      * @see #delete
1082      *
1083      * @since 1.2
1084      */
1085     public void deleteOnExit() {
1086         SecurityManager security = System.getSecurityManager();
1087         if (security != null) {
1088             security.checkDelete(path);
1089         }
1090         if (isInvalid()) {
1091             return;
1092         }
1093         DeleteOnExitHook.add(path);
1094     }
1095 
1096     /**
1097      * Returns an array of strings naming the files and directories in the
1098      * directory denoted by this abstract pathname.
1099      *
1100      * <p> If this abstract pathname does not denote a directory, then this
1101      * method returns {@code null}.  Otherwise an array of strings is
1102      * returned, one for each file or directory in the directory.  Names
1103      * denoting the directory itself and the directory's parent directory are
1104      * not included in the result.  Each string is a file name rather than a
1105      * complete path.
1106      *
1107      * <p> There is no guarantee that the name strings in the resulting array
1108      * will appear in any specific order; they are not, in particular,
1109      * guaranteed to appear in alphabetical order.
1110      *
1111      * <p> Note that the {@link java.nio.file.Files} class defines the {@link
1112      * java.nio.file.Files#newDirectoryStream(Path) newDirectoryStream} method to
1113      * open a directory and iterate over the names of the files in the directory.
1114      * This may use less resources when working with very large directories, and
1115      * may be more responsive when working with remote directories.
1116      *
1117      * @return  An array of strings naming the files and directories in the
1118      *          directory denoted by this abstract pathname.  The array will be
1119      *          empty if the directory is empty.  Returns {@code null} if
1120      *          this abstract pathname does not denote a directory, or if an
1121      *          I/O error occurs.
1122      *
1123      * @throws  SecurityException
1124      *          If a security manager exists and its {@link
1125      *          SecurityManager#checkRead(String)} method denies read access to
1126      *          the directory
1127      */
1128     public String[] list() {
1129         SecurityManager security = System.getSecurityManager();
1130         if (security != null) {
1131             security.checkRead(path);
1132         }
1133         if (isInvalid()) {
1134             return null;
1135         }
1136         return fs.list(this);
1137     }
1138 
1139     /**
1140      * Returns an array of strings naming the files and directories in the
1141      * directory denoted by this abstract pathname that satisfy the specified
1142      * filter.  The behavior of this method is the same as that of the
1143      * {@link #list()} method, except that the strings in the returned array
1144      * must satisfy the filter.  If the given {@code filter} is {@code null}
1145      * then all names are accepted.  Otherwise, a name satisfies the filter if
1146      * and only if the value {@code true} results when the {@link
1147      * FilenameFilter#accept FilenameFilter.accept(File,&nbsp;String)} method
1148      * of the filter is invoked on this abstract pathname and the name of a
1149      * file or directory in the directory that it denotes.
1150      *
1151      * @param  filter
1152      *         A filename filter
1153      *
1154      * @return  An array of strings naming the files and directories in the
1155      *          directory denoted by this abstract pathname that were accepted
1156      *          by the given {@code filter}.  The array will be empty if the
1157      *          directory is empty or if no names were accepted by the filter.
1158      *          Returns {@code null} if this abstract pathname does not denote
1159      *          a directory, or if an I/O error occurs.
1160      *
1161      * @throws  SecurityException
1162      *          If a security manager exists and its {@link
1163      *          SecurityManager#checkRead(String)} method denies read access to
1164      *          the directory
1165      *
1166      * @see java.nio.file.Files#newDirectoryStream(Path,String)
1167      */
1168     public String[] list(FilenameFilter filter) {
1169         String names[] = list();
1170         if ((names == null) || (filter == null)) {
1171             return names;
1172         }
1173         List<String> v = new ArrayList<>();
1174         for (int i = 0 ; i < names.length ; i++) {
1175             if (filter.accept(this, names[i])) {
1176                 v.add(names[i]);
1177             }
1178         }
1179         return v.toArray(new String[v.size()]);
1180     }
1181 
1182     /**
1183      * Returns an array of abstract pathnames denoting the files in the
1184      * directory denoted by this abstract pathname.
1185      *
1186      * <p> If this abstract pathname does not denote a directory, then this
1187      * method returns {@code null}.  Otherwise an array of {@code File} objects
1188      * is returned, one for each file or directory in the directory.  Pathnames
1189      * denoting the directory itself and the directory's parent directory are
1190      * not included in the result.  Each resulting abstract pathname is
1191      * constructed from this abstract pathname using the {@link #File(File,
1192      * String) File(File,&nbsp;String)} constructor.  Therefore if this
1193      * pathname is absolute then each resulting pathname is absolute; if this
1194      * pathname is relative then each resulting pathname will be relative to
1195      * the same directory.
1196      *
1197      * <p> There is no guarantee that the name strings in the resulting array
1198      * will appear in any specific order; they are not, in particular,
1199      * guaranteed to appear in alphabetical order.
1200      *
1201      * <p> Note that the {@link java.nio.file.Files} class defines the {@link
1202      * java.nio.file.Files#newDirectoryStream(Path) newDirectoryStream} method
1203      * to open a directory and iterate over the names of the files in the
1204      * directory. This may use less resources when working with very large
1205      * directories.
1206      *
1207      * @return  An array of abstract pathnames denoting the files and
1208      *          directories in the directory denoted by this abstract pathname.
1209      *          The array will be empty if the directory is empty.  Returns
1210      *          {@code null} if this abstract pathname does not denote a
1211      *          directory, or if an I/O error occurs.
1212      *
1213      * @throws  SecurityException
1214      *          If a security manager exists and its {@link
1215      *          SecurityManager#checkRead(String)} method denies read access to
1216      *          the directory
1217      *
1218      * @since  1.2
1219      */
1220     public File[] listFiles() {
1221         String[] ss = list();
1222         if (ss == null) return null;
1223         int n = ss.length;
1224         File[] fs = new File[n];
1225         for (int i = 0; i < n; i++) {
1226             fs[i] = new File(ss[i], this);
1227         }
1228         return fs;
1229     }
1230 
1231     /**
1232      * Returns an array of abstract pathnames denoting the files and
1233      * directories in the directory denoted by this abstract pathname that
1234      * satisfy the specified filter.  The behavior of this method is the same
1235      * as that of the {@link #listFiles()} method, except that the pathnames in
1236      * the returned array must satisfy the filter.  If the given {@code filter}
1237      * is {@code null} then all pathnames are accepted.  Otherwise, a pathname
1238      * satisfies the filter if and only if the value {@code true} results when
1239      * the {@link FilenameFilter#accept
1240      * FilenameFilter.accept(File,&nbsp;String)} method of the filter is
1241      * invoked on this abstract pathname and the name of a file or directory in
1242      * the directory that it denotes.
1243      *
1244      * @param  filter
1245      *         A filename filter
1246      *
1247      * @return  An array of abstract pathnames denoting the files and
1248      *          directories in the directory denoted by this abstract pathname.
1249      *          The array will be empty if the directory is empty.  Returns
1250      *          {@code null} if this abstract pathname does not denote a
1251      *          directory, or if an I/O error occurs.
1252      *
1253      * @throws  SecurityException
1254      *          If a security manager exists and its {@link
1255      *          SecurityManager#checkRead(String)} method denies read access to
1256      *          the directory
1257      *
1258      * @since  1.2
1259      * @see java.nio.file.Files#newDirectoryStream(Path,String)
1260      */
1261     public File[] listFiles(FilenameFilter filter) {
1262         String ss[] = list();
1263         if (ss == null) return null;
1264         ArrayList<File> files = new ArrayList<>();
1265         for (String s : ss)
1266             if ((filter == null) || filter.accept(this, s))
1267                 files.add(new File(s, this));
1268         return files.toArray(new File[files.size()]);
1269     }
1270 
1271     /**
1272      * Returns an array of abstract pathnames denoting the files and
1273      * directories in the directory denoted by this abstract pathname that
1274      * satisfy the specified filter.  The behavior of this method is the same
1275      * as that of the {@link #listFiles()} method, except that the pathnames in
1276      * the returned array must satisfy the filter.  If the given {@code filter}
1277      * is {@code null} then all pathnames are accepted.  Otherwise, a pathname
1278      * satisfies the filter if and only if the value {@code true} results when
1279      * the {@link FileFilter#accept FileFilter.accept(File)} method of the
1280      * filter is invoked on the pathname.
1281      *
1282      * @param  filter
1283      *         A file filter
1284      *
1285      * @return  An array of abstract pathnames denoting the files and
1286      *          directories in the directory denoted by this abstract pathname.
1287      *          The array will be empty if the directory is empty.  Returns
1288      *          {@code null} if this abstract pathname does not denote a
1289      *          directory, or if an I/O error occurs.
1290      *
1291      * @throws  SecurityException
1292      *          If a security manager exists and its {@link
1293      *          SecurityManager#checkRead(String)} method denies read access to
1294      *          the directory
1295      *
1296      * @since  1.2
1297      * @see java.nio.file.Files#newDirectoryStream(Path,java.nio.file.DirectoryStream.Filter)
1298      */
1299     public File[] listFiles(FileFilter filter) {
1300         String ss[] = list();
1301         if (ss == null) return null;
1302         ArrayList<File> files = new ArrayList<>();
1303         for (String s : ss) {
1304             File f = new File(s, this);
1305             if ((filter == null) || filter.accept(f))
1306                 files.add(f);
1307         }
1308         return files.toArray(new File[files.size()]);
1309     }
1310 
1311     /**
1312      * Creates the directory named by this abstract pathname.
1313      *
1314      * @return  <code>true</code> if and only if the directory was
1315      *          created; <code>false</code> otherwise
1316      *
1317      * @throws  SecurityException
1318      *          If a security manager exists and its {@link
1319      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1320      *          method does not permit the named directory to be created
1321      */
1322     public boolean mkdir() {
1323         SecurityManager security = System.getSecurityManager();
1324         if (security != null) {
1325             security.checkWrite(path);
1326         }
1327         if (isInvalid()) {
1328             return false;
1329         }
1330         return fs.createDirectory(this);
1331     }
1332 
1333     /**
1334      * Creates the directory named by this abstract pathname, including any
1335      * necessary but nonexistent parent directories.  Note that if this
1336      * operation fails it may have succeeded in creating some of the necessary
1337      * parent directories.
1338      *
1339      * @return  <code>true</code> if and only if the directory was created,
1340      *          along with all necessary parent directories; <code>false</code>
1341      *          otherwise
1342      *
1343      * @throws  SecurityException
1344      *          If a security manager exists and its {@link
1345      *          java.lang.SecurityManager#checkRead(java.lang.String)}
1346      *          method does not permit verification of the existence of the
1347      *          named directory and all necessary parent directories; or if
1348      *          the {@link
1349      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1350      *          method does not permit the named directory and all necessary
1351      *          parent directories to be created
1352      */
1353     public boolean mkdirs() {
1354         if (exists()) {
1355             return false;
1356         }
1357         if (mkdir()) {
1358             return true;
1359         }
1360         File canonFile = null;
1361         try {
1362             canonFile = getCanonicalFile();
1363         } catch (IOException e) {
1364             return false;
1365         }
1366 
1367         File parent = canonFile.getParentFile();
1368         return (parent != null && (parent.mkdirs() || parent.exists()) &&
1369                 canonFile.mkdir());
1370     }
1371 
1372     /**
1373      * Renames the file denoted by this abstract pathname.
1374      *
1375      * <p> Many aspects of the behavior of this method are inherently
1376      * platform-dependent: The rename operation might not be able to move a
1377      * file from one filesystem to another, it might not be atomic, and it
1378      * might not succeed if a file with the destination abstract pathname
1379      * already exists.  The return value should always be checked to make sure
1380      * that the rename operation was successful.
1381      *
1382      * <p> Note that the {@link java.nio.file.Files} class defines the {@link
1383      * java.nio.file.Files#move move} method to move or rename a file in a
1384      * platform independent manner.
1385      *
1386      * @param  dest  The new abstract pathname for the named file
1387      *
1388      * @return  <code>true</code> if and only if the renaming succeeded;
1389      *          <code>false</code> otherwise
1390      *
1391      * @throws  SecurityException
1392      *          If a security manager exists and its {@link
1393      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1394      *          method denies write access to either the old or new pathnames
1395      *
1396      * @throws  NullPointerException
1397      *          If parameter <code>dest</code> is <code>null</code>
1398      */
1399     public boolean renameTo(File dest) {
1400         if (dest == null) {
1401             throw new NullPointerException();
1402         }
1403         SecurityManager security = System.getSecurityManager();
1404         if (security != null) {
1405             security.checkWrite(path);
1406             security.checkWrite(dest.path);
1407         }
1408         if (this.isInvalid() || dest.isInvalid()) {
1409             return false;
1410         }
1411         return fs.rename(this, dest);
1412     }
1413 
1414     /**
1415      * Sets the last-modified time of the file or directory named by this
1416      * abstract pathname.
1417      *
1418      * <p> All platforms support file-modification times to the nearest second,
1419      * but some provide more precision.  The argument will be truncated to fit
1420      * the supported precision.  If the operation succeeds and no intervening
1421      * operations on the file take place, then the next invocation of the
1422      * {@link #lastModified} method will return the (possibly
1423      * truncated) <code>time</code> argument that was passed to this method.
1424      *
1425      * @param  time  The new last-modified time, measured in milliseconds since
1426      *               the epoch (00:00:00 GMT, January 1, 1970)
1427      *
1428      * @return <code>true</code> if and only if the operation succeeded;
1429      *          <code>false</code> otherwise
1430      *
1431      * @throws  IllegalArgumentException  If the argument is negative
1432      *
1433      * @throws  SecurityException
1434      *          If a security manager exists and its {@link
1435      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1436      *          method denies write access to the named file
1437      *
1438      * @since 1.2
1439      */
1440     public boolean setLastModified(long time) {
1441         if (time < 0) throw new IllegalArgumentException("Negative time");
1442         SecurityManager security = System.getSecurityManager();
1443         if (security != null) {
1444             security.checkWrite(path);
1445         }
1446         if (isInvalid()) {
1447             return false;
1448         }
1449         return fs.setLastModifiedTime(this, time);
1450     }
1451 
1452     /**
1453      * Marks the file or directory named by this abstract pathname so that
1454      * only read operations are allowed. After invoking this method the file
1455      * or directory will not change until it is either deleted or marked
1456      * to allow write access. On some platforms it may be possible to start the
1457      * Java virtual machine with special privileges that allow it to modify
1458      * files that are marked read-only. Whether or not a read-only file or
1459      * directory may be deleted depends upon the underlying system.
1460      *
1461      * @return <code>true</code> if and only if the operation succeeded;
1462      *          <code>false</code> otherwise
1463      *
1464      * @throws  SecurityException
1465      *          If a security manager exists and its {@link
1466      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1467      *          method denies write access to the named file
1468      *
1469      * @since 1.2
1470      */
1471     public boolean setReadOnly() {
1472         SecurityManager security = System.getSecurityManager();
1473         if (security != null) {
1474             security.checkWrite(path);
1475         }
1476         if (isInvalid()) {
1477             return false;
1478         }
1479         return fs.setReadOnly(this);
1480     }
1481 
1482     /**
1483      * Sets the owner's or everybody's write permission for this abstract
1484      * pathname. On some platforms it may be possible to start the Java virtual
1485      * machine with special privileges that allow it to modify files that
1486      * disallow write operations.
1487      *
1488      * <p> The {@link java.nio.file.Files} class defines methods that operate on
1489      * file attributes including file permissions. This may be used when finer
1490      * manipulation of file permissions is required.
1491      *
1492      * @param   writable
1493      *          If <code>true</code>, sets the access permission to allow write
1494      *          operations; if <code>false</code> to disallow write operations
1495      *
1496      * @param   ownerOnly
1497      *          If <code>true</code>, the write permission applies only to the
1498      *          owner's write permission; otherwise, it applies to everybody.  If
1499      *          the underlying file system can not distinguish the owner's write
1500      *          permission from that of others, then the permission will apply to
1501      *          everybody, regardless of this value.
1502      *
1503      * @return  <code>true</code> if and only if the operation succeeded. The
1504      *          operation will fail if the user does not have permission to change
1505      *          the access permissions of this abstract pathname.
1506      *
1507      * @throws  SecurityException
1508      *          If a security manager exists and its {@link
1509      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1510      *          method denies write access to the named file
1511      *
1512      * @since 1.6
1513      */
1514     public boolean setWritable(boolean writable, boolean ownerOnly) {
1515         SecurityManager security = System.getSecurityManager();
1516         if (security != null) {
1517             security.checkWrite(path);
1518         }
1519         if (isInvalid()) {
1520             return false;
1521         }
1522         return fs.setPermission(this, FileSystem.ACCESS_WRITE, writable, ownerOnly);
1523     }
1524 
1525     /**
1526      * A convenience method to set the owner's write permission for this abstract
1527      * pathname. On some platforms it may be possible to start the Java virtual
1528      * machine with special privileges that allow it to modify files that
1529      * disallow write operations.
1530      *
1531      * <p> An invocation of this method of the form {@code file.setWritable(arg)}
1532      * behaves in exactly the same way as the invocation
1533      *
1534      * <pre>{@code
1535      *     file.setWritable(arg, true)
1536      * }</pre>
1537      *
1538      * @param   writable
1539      *          If <code>true</code>, sets the access permission to allow write
1540      *          operations; if <code>false</code> to disallow write operations
1541      *
1542      * @return  <code>true</code> if and only if the operation succeeded.  The
1543      *          operation will fail if the user does not have permission to
1544      *          change the access permissions of this abstract pathname.
1545      *
1546      * @throws  SecurityException
1547      *          If a security manager exists and its {@link
1548      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1549      *          method denies write access to the file
1550      *
1551      * @since 1.6
1552      */
1553     public boolean setWritable(boolean writable) {
1554         return setWritable(writable, true);
1555     }
1556 
1557     /**
1558      * Sets the owner's or everybody's read permission for this abstract
1559      * pathname. On some platforms it may be possible to start the Java virtual
1560      * machine with special privileges that allow it to read files that are
1561      * marked as unreadable.
1562      *
1563      * <p> The {@link java.nio.file.Files} class defines methods that operate on
1564      * file attributes including file permissions. This may be used when finer
1565      * manipulation of file permissions is required.
1566      *
1567      * @param   readable
1568      *          If <code>true</code>, sets the access permission to allow read
1569      *          operations; if <code>false</code> to disallow read operations
1570      *
1571      * @param   ownerOnly
1572      *          If <code>true</code>, the read permission applies only to the
1573      *          owner's read permission; otherwise, it applies to everybody.  If
1574      *          the underlying file system can not distinguish the owner's read
1575      *          permission from that of others, then the permission will apply to
1576      *          everybody, regardless of this value.
1577      *
1578      * @return  <code>true</code> if and only if the operation succeeded.  The
1579      *          operation will fail if the user does not have permission to
1580      *          change the access permissions of this abstract pathname.  If
1581      *          <code>readable</code> is <code>false</code> and the underlying
1582      *          file system does not implement a read permission, then the
1583      *          operation will fail.
1584      *
1585      * @throws  SecurityException
1586      *          If a security manager exists and its {@link
1587      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1588      *          method denies write access to the file
1589      *
1590      * @since 1.6
1591      */
1592     public boolean setReadable(boolean readable, boolean ownerOnly) {
1593         SecurityManager security = System.getSecurityManager();
1594         if (security != null) {
1595             security.checkWrite(path);
1596         }
1597         if (isInvalid()) {
1598             return false;
1599         }
1600         return fs.setPermission(this, FileSystem.ACCESS_READ, readable, ownerOnly);
1601     }
1602 
1603     /**
1604      * A convenience method to set the owner's read permission for this abstract
1605      * pathname. On some platforms it may be possible to start the Java virtual
1606      * machine with special privileges that allow it to read files that are
1607      * marked as unreadable.
1608      *
1609      * <p>An invocation of this method of the form {@code file.setReadable(arg)}
1610      * behaves in exactly the same way as the invocation
1611      *
1612      * <pre>{@code
1613      *     file.setReadable(arg, true)
1614      * }</pre>
1615      *
1616      * @param  readable
1617      *          If <code>true</code>, sets the access permission to allow read
1618      *          operations; if <code>false</code> to disallow read operations
1619      *
1620      * @return  <code>true</code> if and only if the operation succeeded.  The
1621      *          operation will fail if the user does not have permission to
1622      *          change the access permissions of this abstract pathname.  If
1623      *          <code>readable</code> is <code>false</code> and the underlying
1624      *          file system does not implement a read permission, then the
1625      *          operation will fail.
1626      *
1627      * @throws  SecurityException
1628      *          If a security manager exists and its {@link
1629      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1630      *          method denies write access to the file
1631      *
1632      * @since 1.6
1633      */
1634     public boolean setReadable(boolean readable) {
1635         return setReadable(readable, true);
1636     }
1637 
1638     /**
1639      * Sets the owner's or everybody's execute permission for this abstract
1640      * pathname. On some platforms it may be possible to start the Java virtual
1641      * machine with special privileges that allow it to execute files that are
1642      * not marked executable.
1643      *
1644      * <p> The {@link java.nio.file.Files} class defines methods that operate on
1645      * file attributes including file permissions. This may be used when finer
1646      * manipulation of file permissions is required.
1647      *
1648      * @param   executable
1649      *          If <code>true</code>, sets the access permission to allow execute
1650      *          operations; if <code>false</code> to disallow execute operations
1651      *
1652      * @param   ownerOnly
1653      *          If <code>true</code>, the execute permission applies only to the
1654      *          owner's execute permission; otherwise, it applies to everybody.
1655      *          If the underlying file system can not distinguish the owner's
1656      *          execute permission from that of others, then the permission will
1657      *          apply to everybody, regardless of this value.
1658      *
1659      * @return  <code>true</code> if and only if the operation succeeded.  The
1660      *          operation will fail if the user does not have permission to
1661      *          change the access permissions of this abstract pathname.  If
1662      *          <code>executable</code> is <code>false</code> and the underlying
1663      *          file system does not implement an execute permission, then the
1664      *          operation will fail.
1665      *
1666      * @throws  SecurityException
1667      *          If a security manager exists and its {@link
1668      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1669      *          method denies write access to the file
1670      *
1671      * @since 1.6
1672      */
1673     public boolean setExecutable(boolean executable, boolean ownerOnly) {
1674         SecurityManager security = System.getSecurityManager();
1675         if (security != null) {
1676             security.checkWrite(path);
1677         }
1678         if (isInvalid()) {
1679             return false;
1680         }
1681         return fs.setPermission(this, FileSystem.ACCESS_EXECUTE, executable, ownerOnly);
1682     }
1683 
1684     /**
1685      * A convenience method to set the owner's execute permission for this
1686      * abstract pathname. On some platforms it may be possible to start the Java
1687      * virtual machine with special privileges that allow it to execute files
1688      * that are not marked executable.
1689      *
1690      * <p>An invocation of this method of the form {@code file.setExcutable(arg)}
1691      * behaves in exactly the same way as the invocation
1692      *
1693      * <pre>{@code
1694      *     file.setExecutable(arg, true)
1695      * }</pre>
1696      *
1697      * @param   executable
1698      *          If <code>true</code>, sets the access permission to allow execute
1699      *          operations; if <code>false</code> to disallow execute operations
1700      *
1701      * @return   <code>true</code> if and only if the operation succeeded.  The
1702      *           operation will fail if the user does not have permission to
1703      *           change the access permissions of this abstract pathname.  If
1704      *           <code>executable</code> is <code>false</code> and the underlying
1705      *           file system does not implement an execute permission, then the
1706      *           operation will fail.
1707      *
1708      * @throws  SecurityException
1709      *          If a security manager exists and its {@link
1710      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1711      *          method denies write access to the file
1712      *
1713      * @since 1.6
1714      */
1715     public boolean setExecutable(boolean executable) {
1716         return setExecutable(executable, true);
1717     }
1718 
1719     /**
1720      * Tests whether the application can execute the file denoted by this
1721      * abstract pathname. On some platforms it may be possible to start the
1722      * Java virtual machine with special privileges that allow it to execute
1723      * files that are not marked executable. Consequently this method may return
1724      * {@code true} even though the file does not have execute permissions.
1725      *
1726      * @return  <code>true</code> if and only if the abstract pathname exists
1727      *          <em>and</em> the application is allowed to execute the file
1728      *
1729      * @throws  SecurityException
1730      *          If a security manager exists and its {@link
1731      *          java.lang.SecurityManager#checkExec(java.lang.String)}
1732      *          method denies execute access to the file
1733      *
1734      * @since 1.6
1735      */
1736     public boolean canExecute() {
1737         SecurityManager security = System.getSecurityManager();
1738         if (security != null) {
1739             security.checkExec(path);
1740         }
1741         if (isInvalid()) {
1742             return false;
1743         }
1744         return fs.checkAccess(this, FileSystem.ACCESS_EXECUTE);
1745     }
1746 
1747 
1748     /* -- Filesystem interface -- */
1749 
1750     /**
1751      * List the available filesystem roots.
1752      *
1753      * <p> A particular Java platform may support zero or more
1754      * hierarchically-organized file systems.  Each file system has a
1755      * {@code root} directory from which all other files in that file system
1756      * can be reached.  Windows platforms, for example, have a root directory
1757      * for each active drive; UNIX platforms have a single root directory,
1758      * namely {@code "/"}.  The set of available filesystem roots is affected
1759      * by various system-level operations such as the insertion or ejection of
1760      * removable media and the disconnecting or unmounting of physical or
1761      * virtual disk drives.
1762      *
1763      * <p> This method returns an array of {@code File} objects that denote the
1764      * root directories of the available filesystem roots.  It is guaranteed
1765      * that the canonical pathname of any file physically present on the local
1766      * machine will begin with one of the roots returned by this method.
1767      *
1768      * <p> The canonical pathname of a file that resides on some other machine
1769      * and is accessed via a remote-filesystem protocol such as SMB or NFS may
1770      * or may not begin with one of the roots returned by this method.  If the
1771      * pathname of a remote file is syntactically indistinguishable from the
1772      * pathname of a local file then it will begin with one of the roots
1773      * returned by this method.  Thus, for example, {@code File} objects
1774      * denoting the root directories of the mapped network drives of a Windows
1775      * platform will be returned by this method, while {@code File} objects
1776      * containing UNC pathnames will not be returned by this method.
1777      *
1778      * <p> Unlike most methods in this class, this method does not throw
1779      * security exceptions.  If a security manager exists and its {@link
1780      * SecurityManager#checkRead(String)} method denies read access to a
1781      * particular root directory, then that directory will not appear in the
1782      * result.
1783      *
1784      * @return  An array of {@code File} objects denoting the available
1785      *          filesystem roots, or {@code null} if the set of roots could not
1786      *          be determined.  The array will be empty if there are no
1787      *          filesystem roots.
1788      *
1789      * @since  1.2
1790      * @see java.nio.file.FileStore
1791      */
1792     public static File[] listRoots() {
1793         return fs.listRoots();
1794     }
1795 
1796 
1797     /* -- Disk usage -- */
1798 
1799     /**
1800      * Returns the size of the partition <a href="#partName">named</a> by this
1801      * abstract pathname.
1802      *
1803      * @return  The size, in bytes, of the partition or {@code 0L} if this
1804      *          abstract pathname does not name a partition
1805      *
1806      * @throws  SecurityException
1807      *          If a security manager has been installed and it denies
1808      *          {@link RuntimePermission}{@code ("getFileSystemAttributes")}
1809      *          or its {@link SecurityManager#checkRead(String)} method denies
1810      *          read access to the file named by this abstract pathname
1811      *
1812      * @since  1.6
1813      */
1814     public long getTotalSpace() {
1815         SecurityManager sm = System.getSecurityManager();
1816         if (sm != null) {
1817             sm.checkPermission(new RuntimePermission("getFileSystemAttributes"));
1818             sm.checkRead(path);
1819         }
1820         if (isInvalid()) {
1821             return 0L;
1822         }
1823         return fs.getSpace(this, FileSystem.SPACE_TOTAL);
1824     }
1825 
1826     /**
1827      * Returns the number of unallocated bytes in the partition <a
1828      * href="#partName">named</a> by this abstract path name.
1829      *
1830      * <p> The returned number of unallocated bytes is a hint, but not
1831      * a guarantee, that it is possible to use most or any of these
1832      * bytes.  The number of unallocated bytes is most likely to be
1833      * accurate immediately after this call.  It is likely to be made
1834      * inaccurate by any external I/O operations including those made
1835      * on the system outside of this virtual machine.  This method
1836      * makes no guarantee that write operations to this file system
1837      * will succeed.
1838      *
1839      * @return  The number of unallocated bytes on the partition or {@code 0L}
1840      *          if the abstract pathname does not name a partition.  This
1841      *          value will be less than or equal to the total file system size
1842      *          returned by {@link #getTotalSpace}.
1843      *
1844      * @throws  SecurityException
1845      *          If a security manager has been installed and it denies
1846      *          {@link RuntimePermission}{@code ("getFileSystemAttributes")}
1847      *          or its {@link SecurityManager#checkRead(String)} method denies
1848      *          read access to the file named by this abstract pathname
1849      *
1850      * @since  1.6
1851      */
1852     public long getFreeSpace() {
1853         SecurityManager sm = System.getSecurityManager();
1854         if (sm != null) {
1855             sm.checkPermission(new RuntimePermission("getFileSystemAttributes"));
1856             sm.checkRead(path);
1857         }
1858         if (isInvalid()) {
1859             return 0L;
1860         }
1861         return fs.getSpace(this, FileSystem.SPACE_FREE);
1862     }
1863 
1864     /**
1865      * Returns the number of bytes available to this virtual machine on the
1866      * partition <a href="#partName">named</a> by this abstract pathname.  When
1867      * possible, this method checks for write permissions and other operating
1868      * system restrictions and will therefore usually provide a more accurate
1869      * estimate of how much new data can actually be written than {@link
1870      * #getFreeSpace}.
1871      *
1872      * <p> The returned number of available bytes is a hint, but not a
1873      * guarantee, that it is possible to use most or any of these bytes.  The
1874      * number of available bytes is most likely to be accurate immediately
1875      * after this call.  It is likely to be made inaccurate by any external
1876      * I/O operations including those made on the system outside of this
1877      * virtual machine.  This method makes no guarantee that write operations
1878      * to this file system will succeed.
1879      *
1880      * @return  The number of available bytes on the partition or {@code 0L}
1881      *          if the abstract pathname does not name a partition.  On
1882      *          systems where this information is not available, this method
1883      *          will be equivalent to a call to {@link #getFreeSpace}.
1884      *
1885      * @throws  SecurityException
1886      *          If a security manager has been installed and it denies
1887      *          {@link RuntimePermission}{@code ("getFileSystemAttributes")}
1888      *          or its {@link SecurityManager#checkRead(String)} method denies
1889      *          read access to the file named by this abstract pathname
1890      *
1891      * @since  1.6
1892      */
1893     public long getUsableSpace() {
1894         SecurityManager sm = System.getSecurityManager();
1895         if (sm != null) {
1896             sm.checkPermission(new RuntimePermission("getFileSystemAttributes"));
1897             sm.checkRead(path);
1898         }
1899         if (isInvalid()) {
1900             return 0L;
1901         }
1902         return fs.getSpace(this, FileSystem.SPACE_USABLE);
1903     }
1904 
1905     /* -- Temporary files -- */
1906 
1907     private static class TempDirectory {
1908         private TempDirectory() { }
1909 
1910         // temporary directory location
1911         private static final File tmpdir = new File(
1912                 GetPropertyAction.privilegedGetProperty("java.io.tmpdir"));
1913         static File location() {
1914             return tmpdir;
1915         }
1916 
1917         // file name generation
1918         private static final SecureRandom random = new SecureRandom();
1919         private static int shortenSubName(int subNameLength, int excess,
1920             int nameMin) {
1921             int newLength = Math.max(nameMin, subNameLength - excess);
1922             if (newLength < subNameLength) {
1923                 return newLength;
1924             }
1925             return subNameLength;
1926         }
1927         static File generateFile(String prefix, String suffix, File dir)
1928             throws IOException
1929         {
1930             long n = random.nextLong();
1931             String nus = Long.toUnsignedString(n);
1932 
1933             // Use only the file name from the supplied prefix
1934             prefix = (new File(prefix)).getName();
1935 
1936             int prefixLength = prefix.length();
1937             int nusLength = nus.length();
1938             int suffixLength = suffix.length();;
1939 
1940             String name;
1941             int nameMax = fs.getNameMax(dir.getPath());
1942             int excess = prefixLength + nusLength + suffixLength - nameMax;
1943             if (excess <= 0) {
1944                 name = prefix + nus + suffix;
1945             } else {
1946                 // Name exceeds the maximum path component length: shorten it
1947 
1948                 // Attempt to shorten the prefix length to no less then 3
1949                 prefixLength = shortenSubName(prefixLength, excess, 3);
1950                 excess = prefixLength + nusLength + suffixLength - nameMax;
1951 
1952                 if (excess > 0) {
1953                     // Attempt to shorten the suffix length to no less than
1954                     // 0 or 4 depending on whether it begins with a dot ('.')
1955                     suffixLength = shortenSubName(suffixLength, excess,
1956                         suffix.indexOf(".") == 0 ? 4 : 0);
1957                     suffixLength = shortenSubName(suffixLength, excess, 3);
1958                     excess = prefixLength + nusLength + suffixLength - nameMax;
1959                 }
1960 
1961                 if (excess > 0 && excess <= nusLength - 5) {
1962                     // Attempt to shorten the random character string length
1963                     // to no less than 5
1964                     nusLength = shortenSubName(nusLength, excess, 5);
1965                 }
1966 
1967                 StringBuilder sb =
1968                     new StringBuilder(prefixLength + nusLength + suffixLength);
1969                 sb.append(prefixLength < prefix.length() ?
1970                     prefix.substring(0, prefixLength) : prefix);
1971                 sb.append(nusLength < nus.length() ?
1972                     nus.substring(0, nusLength) : nus);
1973                 sb.append(suffixLength < suffix.length() ?
1974                     suffix.substring(0, suffixLength) : suffix);
1975                 name = sb.toString();
1976             }
1977 
1978             // Normalize the path component
1979             name = fs.normalize(name);
1980 
1981             File f = new File(dir, name);
1982             if (!name.equals(f.getName()) || f.isInvalid()) {
1983                 if (System.getSecurityManager() != null)
1984                     throw new IOException("Unable to create temporary file");
1985                 else
1986                     throw new IOException("Unable to create temporary file, "
1987                         + name);
1988             }
1989             return f;
1990         }
1991     }
1992 
1993     /**
1994      * <p> Creates a new empty file in the specified directory, using the
1995      * given prefix and suffix strings to generate its name.  If this method
1996      * returns successfully then it is guaranteed that:
1997      *
1998      * <ol>
1999      * <li> The file denoted by the returned abstract pathname did not exist
2000      *      before this method was invoked, and
2001      * <li> Neither this method nor any of its variants will return the same
2002      *      abstract pathname again in the current invocation of the virtual
2003      *      machine.
2004      * </ol>
2005      *
2006      * This method provides only part of a temporary-file facility.  To arrange
2007      * for a file created by this method to be deleted automatically, use the
2008      * {@link #deleteOnExit} method.
2009      *
2010      * <p> The <code>prefix</code> argument must be at least three characters
2011      * long.  It is recommended that the prefix be a short, meaningful string
2012      * such as <code>"hjb"</code> or <code>"mail"</code>.  The
2013      * <code>suffix</code> argument may be <code>null</code>, in which case the
2014      * suffix <code>".tmp"</code> will be used.
2015      *
2016      * <p> To create the new file, the prefix and the suffix may first be
2017      * adjusted to fit the limitations of the underlying platform.  If the
2018      * prefix is too long then it will be truncated, but its first three
2019      * characters will always be preserved.  If the suffix is too long then it
2020      * too will be truncated, but if it begins with a period character
2021      * (<code>'.'</code>) then the period and the first three characters
2022      * following it will always be preserved.  Once these adjustments have been
2023      * made the name of the new file will be generated by concatenating the
2024      * prefix, five or more internally-generated characters, and the suffix.
2025      *
2026      * <p> If the <code>directory</code> argument is <code>null</code> then the
2027      * system-dependent default temporary-file directory will be used.  The
2028      * default temporary-file directory is specified by the system property
2029      * <code>java.io.tmpdir</code>.  On UNIX systems the default value of this
2030      * property is typically <code>"/tmp"</code> or <code>"/var/tmp"</code>; on
2031      * Microsoft Windows systems it is typically <code>"C:\\WINNT\\TEMP"</code>.  A different
2032      * value may be given to this system property when the Java virtual machine
2033      * is invoked, but programmatic changes to this property are not guaranteed
2034      * to have any effect upon the temporary directory used by this method.
2035      *
2036      * @param  prefix     The prefix string to be used in generating the file's
2037      *                    name; must be at least three characters long
2038      *
2039      * @param  suffix     The suffix string to be used in generating the file's
2040      *                    name; may be <code>null</code>, in which case the
2041      *                    suffix <code>".tmp"</code> will be used
2042      *
2043      * @param  directory  The directory in which the file is to be created, or
2044      *                    <code>null</code> if the default temporary-file
2045      *                    directory is to be used
2046      *
2047      * @return  An abstract pathname denoting a newly-created empty file
2048      *
2049      * @throws  IllegalArgumentException
2050      *          If the <code>prefix</code> argument contains fewer than three
2051      *          characters
2052      *
2053      * @throws  IOException  If a file could not be created
2054      *
2055      * @throws  SecurityException
2056      *          If a security manager exists and its {@link
2057      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
2058      *          method does not allow a file to be created
2059      *
2060      * @since 1.2
2061      */
2062     public static File createTempFile(String prefix, String suffix,
2063                                       File directory)
2064         throws IOException
2065     {
2066         if (prefix.length() < 3) {
2067             throw new IllegalArgumentException("Prefix string \"" + prefix +
2068                 "\" too short: length must be at least 3");
2069         }
2070         if (suffix == null)
2071             suffix = ".tmp";
2072 
2073         File tmpdir = (directory != null) ? directory
2074                                           : TempDirectory.location();
2075         SecurityManager sm = System.getSecurityManager();
2076         File f;
2077         do {
2078             f = TempDirectory.generateFile(prefix, suffix, tmpdir);
2079 
2080             if (sm != null) {
2081                 try {
2082                     sm.checkWrite(f.getPath());
2083                 } catch (SecurityException se) {
2084                     // don't reveal temporary directory location
2085                     if (directory == null)
2086                         throw new SecurityException("Unable to create temporary file");
2087                     throw se;
2088                 }
2089             }
2090         } while ((fs.getBooleanAttributes(f) & FileSystem.BA_EXISTS) != 0);
2091 
2092         if (!fs.createFileExclusively(f.getPath()))
2093             throw new IOException("Unable to create temporary file");
2094 
2095         return f;
2096     }
2097 
2098     /**
2099      * Creates an empty file in the default temporary-file directory, using
2100      * the given prefix and suffix to generate its name. Invoking this method
2101      * is equivalent to invoking {@link #createTempFile(java.lang.String,
2102      * java.lang.String, java.io.File)
2103      * createTempFile(prefix,&nbsp;suffix,&nbsp;null)}.
2104      *
2105      * <p> The {@link
2106      * java.nio.file.Files#createTempFile(String,String,java.nio.file.attribute.FileAttribute[])
2107      * Files.createTempFile} method provides an alternative method to create an
2108      * empty file in the temporary-file directory. Files created by that method
2109      * may have more restrictive access permissions to files created by this
2110      * method and so may be more suited to security-sensitive applications.
2111      *
2112      * @param  prefix     The prefix string to be used in generating the file's
2113      *                    name; must be at least three characters long
2114      *
2115      * @param  suffix     The suffix string to be used in generating the file's
2116      *                    name; may be <code>null</code>, in which case the
2117      *                    suffix <code>".tmp"</code> will be used
2118      *
2119      * @return  An abstract pathname denoting a newly-created empty file
2120      *
2121      * @throws  IllegalArgumentException
2122      *          If the <code>prefix</code> argument contains fewer than three
2123      *          characters
2124      *
2125      * @throws  IOException  If a file could not be created
2126      *
2127      * @throws  SecurityException
2128      *          If a security manager exists and its {@link
2129      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
2130      *          method does not allow a file to be created
2131      *
2132      * @since 1.2
2133      * @see java.nio.file.Files#createTempDirectory(String,FileAttribute[])
2134      */
2135     public static File createTempFile(String prefix, String suffix)
2136         throws IOException
2137     {
2138         return createTempFile(prefix, suffix, null);
2139     }
2140 
2141     /* -- Basic infrastructure -- */
2142 
2143     /**
2144      * Compares two abstract pathnames lexicographically.  The ordering
2145      * defined by this method depends upon the underlying system.  On UNIX
2146      * systems, alphabetic case is significant in comparing pathnames; on Microsoft Windows
2147      * systems it is not.
2148      *
2149      * @param   pathname  The abstract pathname to be compared to this abstract
2150      *                    pathname
2151      *
2152      * @return  Zero if the argument is equal to this abstract pathname, a
2153      *          value less than zero if this abstract pathname is
2154      *          lexicographically less than the argument, or a value greater
2155      *          than zero if this abstract pathname is lexicographically
2156      *          greater than the argument
2157      *
2158      * @since   1.2
2159      */
2160     public int compareTo(File pathname) {
2161         return fs.compare(this, pathname);
2162     }
2163 
2164     /**
2165      * Tests this abstract pathname for equality with the given object.
2166      * Returns <code>true</code> if and only if the argument is not
2167      * <code>null</code> and is an abstract pathname that denotes the same file
2168      * or directory as this abstract pathname.  Whether or not two abstract
2169      * pathnames are equal depends upon the underlying system.  On UNIX
2170      * systems, alphabetic case is significant in comparing pathnames; on Microsoft Windows
2171      * systems it is not.
2172      *
2173      * @param   obj   The object to be compared with this abstract pathname
2174      *
2175      * @return  <code>true</code> if and only if the objects are the same;
2176      *          <code>false</code> otherwise
2177      */
2178     public boolean equals(Object obj) {
2179         if ((obj != null) && (obj instanceof File)) {
2180             return compareTo((File)obj) == 0;
2181         }
2182         return false;
2183     }
2184 
2185     /**
2186      * Computes a hash code for this abstract pathname.  Because equality of
2187      * abstract pathnames is inherently system-dependent, so is the computation
2188      * of their hash codes.  On UNIX systems, the hash code of an abstract
2189      * pathname is equal to the exclusive <em>or</em> of the hash code
2190      * of its pathname string and the decimal value
2191      * <code>1234321</code>.  On Microsoft Windows systems, the hash
2192      * code is equal to the exclusive <em>or</em> of the hash code of
2193      * its pathname string converted to lower case and the decimal
2194      * value <code>1234321</code>.  Locale is not taken into account on
2195      * lowercasing the pathname string.
2196      *
2197      * @return  A hash code for this abstract pathname
2198      */
2199     public int hashCode() {
2200         return fs.hashCode(this);
2201     }
2202 
2203     /**
2204      * Returns the pathname string of this abstract pathname.  This is just the
2205      * string returned by the {@link #getPath} method.
2206      *
2207      * @return  The string form of this abstract pathname
2208      */
2209     public String toString() {
2210         return getPath();
2211     }
2212 
2213     /**
2214      * WriteObject is called to save this filename.
2215      * The separator character is saved also so it can be replaced
2216      * in case the path is reconstituted on a different host type.
2217      *
2218      * @serialData  Default fields followed by separator character.
2219      */
2220     private synchronized void writeObject(java.io.ObjectOutputStream s)
2221         throws IOException
2222     {
2223         s.defaultWriteObject();
2224         s.writeChar(separatorChar); // Add the separator character
2225     }
2226 
2227     /**
2228      * readObject is called to restore this filename.
2229      * The original separator character is read.  If it is different
2230      * than the separator character on this system, then the old separator
2231      * is replaced by the local separator.
2232      */
2233     private synchronized void readObject(java.io.ObjectInputStream s)
2234          throws IOException, ClassNotFoundException
2235     {
2236         ObjectInputStream.GetField fields = s.readFields();
2237         String pathField = (String)fields.get("path", null);
2238         char sep = s.readChar(); // read the previous separator char
2239         if (sep != separatorChar)
2240             pathField = pathField.replace(sep, separatorChar);
2241         String path = fs.normalize(pathField);
2242         UNSAFE.putReference(this, PATH_OFFSET, path);
2243         UNSAFE.putIntVolatile(this, PREFIX_LENGTH_OFFSET, fs.prefixLength(path));
2244     }
2245 
2246     private static final jdk.internal.misc.Unsafe UNSAFE
2247             = jdk.internal.misc.Unsafe.getUnsafe();
2248     private static final long PATH_OFFSET
2249             = UNSAFE.objectFieldOffset(File.class, "path");
2250     private static final long PREFIX_LENGTH_OFFSET
2251             = UNSAFE.objectFieldOffset(File.class, "prefixLength");
2252 
2253     /** use serialVersionUID from JDK 1.0.2 for interoperability */
2254     private static final long serialVersionUID = 301077366599181567L;
2255 
2256     // -- Integration with java.nio.file --
2257 
2258     private transient volatile Path filePath;
2259 
2260     /**
2261      * Returns a {@link Path java.nio.file.Path} object constructed from
2262      * this abstract path. The resulting {@code Path} is associated with the
2263      * {@link java.nio.file.FileSystems#getDefault default-filesystem}.
2264      *
2265      * <p> The first invocation of this method works as if invoking it were
2266      * equivalent to evaluating the expression:
2267      * <blockquote><pre>
2268      * {@link java.nio.file.FileSystems#getDefault FileSystems.getDefault}().{@link
2269      * java.nio.file.FileSystem#getPath getPath}(this.{@link #getPath getPath}());
2270      * </pre></blockquote>
2271      * Subsequent invocations of this method return the same {@code Path}.
2272      *
2273      * <p> If this abstract pathname is the empty abstract pathname then this
2274      * method returns a {@code Path} that may be used to access the current
2275      * user directory.
2276      *
2277      * @return  a {@code Path} constructed from this abstract path
2278      *
2279      * @throws  java.nio.file.InvalidPathException
2280      *          if a {@code Path} object cannot be constructed from the abstract
2281      *          path (see {@link java.nio.file.FileSystem#getPath FileSystem.getPath})
2282      *
2283      * @since   1.7
2284      * @see Path#toFile
2285      */
2286     public Path toPath() {
2287         Path result = filePath;
2288         if (result == null) {
2289             synchronized (this) {
2290                 result = filePath;
2291                 if (result == null) {
2292                     result = FileSystems.getDefault().getPath(path);
2293                     filePath = result;
2294                 }
2295             }
2296         }
2297         return result;
2298     }
2299 }