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