1 /*
   2  * Copyright (c) 1994, 2017, 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
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 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.util.List;
  33 import java.util.ArrayList;
  34 import java.security.SecureRandom;
  35 import java.nio.file.Path;
  36 import java.nio.file.FileSystems;
  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  * <h3>Interoperability with {@code java.nio.file} package</h3>
 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.equals(""));
 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.equals("")) {
 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.equals("")) {
 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.equals(""))
 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      * <p> Where it is required to distinguish an I/O exception from the case
 920      * where {@code 0L} is returned, or where several attributes of the
 921      * same file are required at the same time, or where the time of last
 922      * access or the creation time are required, then the {@link
 923      * java.nio.file.Files#readAttributes(Path,Class,LinkOption[])
 924      * Files.readAttributes} method may be used.
 925      *
 926      * @apiNote
 927      * While the unit of time of the return value is milliseconds,
 928      * the granularity of the value depends on the underlying
 929      * file system and may be larger.  For example, some
 930      * file systems use time stamps in units of seconds.
 931      *
 932      * @return  A <code>long</code> value representing the time the file was
 933      *          last modified, measured in milliseconds since the epoch
 934      *          (00:00:00 GMT, January 1, 1970), or <code>0L</code> if the
 935      *          file does not exist or if an I/O error occurs
 936      *
 937      * @throws  SecurityException
 938      *          If a security manager exists and its {@link
 939      *          java.lang.SecurityManager#checkRead(java.lang.String)}
 940      *          method denies read access to the file
 941      */
 942     public long lastModified() {
 943         SecurityManager security = System.getSecurityManager();
 944         if (security != null) {
 945             security.checkRead(path);
 946         }
 947         if (isInvalid()) {
 948             return 0L;
 949         }
 950         return fs.getLastModifiedTime(this);
 951     }
 952 
 953     /**
 954      * Returns the length of the file denoted by this abstract pathname.
 955      * The return value is unspecified if this pathname denotes a directory.
 956      *
 957      * <p> Where it is required to distinguish an I/O exception from the case
 958      * that {@code 0L} is returned, or where several attributes of the same file
 959      * are required at the same time, then the {@link
 960      * java.nio.file.Files#readAttributes(Path,Class,LinkOption[])
 961      * Files.readAttributes} method may be used.
 962      *
 963      * @return  The length, in bytes, of the file denoted by this abstract
 964      *          pathname, or <code>0L</code> if the file does not exist.  Some
 965      *          operating systems may return <code>0L</code> for pathnames
 966      *          denoting system-dependent entities such as devices or pipes.
 967      *
 968      * @throws  SecurityException
 969      *          If a security manager exists and its {@link
 970      *          java.lang.SecurityManager#checkRead(java.lang.String)}
 971      *          method denies read access to the file
 972      */
 973     public long length() {
 974         SecurityManager security = System.getSecurityManager();
 975         if (security != null) {
 976             security.checkRead(path);
 977         }
 978         if (isInvalid()) {
 979             return 0L;
 980         }
 981         return fs.getLength(this);
 982     }
 983 
 984 
 985     /* -- File operations -- */
 986 
 987     /**
 988      * Atomically creates a new, empty file named by this abstract pathname if
 989      * and only if a file with this name does not yet exist.  The check for the
 990      * existence of the file and the creation of the file if it does not exist
 991      * are a single operation that is atomic with respect to all other
 992      * filesystem activities that might affect the file.
 993      * <P>
 994      * Note: this method should <i>not</i> be used for file-locking, as
 995      * the resulting protocol cannot be made to work reliably. The
 996      * {@link java.nio.channels.FileLock FileLock}
 997      * facility should be used instead.
 998      *
 999      * @return  <code>true</code> if the named file does not exist and was
1000      *          successfully created; <code>false</code> if the named file
1001      *          already exists
1002      *
1003      * @throws  IOException
1004      *          If an I/O error occurred
1005      *
1006      * @throws  SecurityException
1007      *          If a security manager exists and its {@link
1008      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1009      *          method denies write access to the file
1010      *
1011      * @since 1.2
1012      */
1013     public boolean createNewFile() throws IOException {
1014         SecurityManager security = System.getSecurityManager();
1015         if (security != null) security.checkWrite(path);
1016         if (isInvalid()) {
1017             throw new IOException("Invalid file path");
1018         }
1019         return fs.createFileExclusively(path);
1020     }
1021 
1022     /**
1023      * Deletes the file or directory denoted by this abstract pathname.  If
1024      * this pathname denotes a directory, then the directory must be empty in
1025      * order to be deleted.
1026      *
1027      * <p> Note that the {@link java.nio.file.Files} class defines the {@link
1028      * java.nio.file.Files#delete(Path) delete} method to throw an {@link IOException}
1029      * when a file cannot be deleted. This is useful for error reporting and to
1030      * diagnose why a file cannot be deleted.
1031      *
1032      * @return  <code>true</code> if and only if the file or directory is
1033      *          successfully deleted; <code>false</code> otherwise
1034      *
1035      * @throws  SecurityException
1036      *          If a security manager exists and its {@link
1037      *          java.lang.SecurityManager#checkDelete} method denies
1038      *          delete access to the file
1039      */
1040     public boolean delete() {
1041         SecurityManager security = System.getSecurityManager();
1042         if (security != null) {
1043             security.checkDelete(path);
1044         }
1045         if (isInvalid()) {
1046             return false;
1047         }
1048         return fs.delete(this);
1049     }
1050 
1051     /**
1052      * Requests that the file or directory denoted by this abstract
1053      * pathname be deleted when the virtual machine terminates.
1054      * Files (or directories) are deleted in the reverse order that
1055      * they are registered. Invoking this method to delete a file or
1056      * directory that is already registered for deletion has no effect.
1057      * Deletion will be attempted only for normal termination of the
1058      * virtual machine, as defined by the Java Language Specification.
1059      *
1060      * <p> Once deletion has been requested, it is not possible to cancel the
1061      * request.  This method should therefore be used with care.
1062      *
1063      * <P>
1064      * Note: this method should <i>not</i> be used for file-locking, as
1065      * the resulting protocol cannot be made to work reliably. The
1066      * {@link java.nio.channels.FileLock FileLock}
1067      * facility should be used instead.
1068      *
1069      * @throws  SecurityException
1070      *          If a security manager exists and its {@link
1071      *          java.lang.SecurityManager#checkDelete} method denies
1072      *          delete access to the file
1073      *
1074      * @see #delete
1075      *
1076      * @since 1.2
1077      */
1078     public void deleteOnExit() {
1079         SecurityManager security = System.getSecurityManager();
1080         if (security != null) {
1081             security.checkDelete(path);
1082         }
1083         if (isInvalid()) {
1084             return;
1085         }
1086         DeleteOnExitHook.add(path);
1087     }
1088 
1089     /**
1090      * Returns an array of strings naming the files and directories in the
1091      * directory denoted by this abstract pathname.
1092      *
1093      * <p> If this abstract pathname does not denote a directory, then this
1094      * method returns {@code null}.  Otherwise an array of strings is
1095      * returned, one for each file or directory in the directory.  Names
1096      * denoting the directory itself and the directory's parent directory are
1097      * not included in the result.  Each string is a file name rather than a
1098      * complete path.
1099      *
1100      * <p> There is no guarantee that the name strings in the resulting array
1101      * will appear in any specific order; they are not, in particular,
1102      * guaranteed to appear in alphabetical order.
1103      *
1104      * <p> Note that the {@link java.nio.file.Files} class defines the {@link
1105      * java.nio.file.Files#newDirectoryStream(Path) newDirectoryStream} method to
1106      * open a directory and iterate over the names of the files in the directory.
1107      * This may use less resources when working with very large directories, and
1108      * may be more responsive when working with remote directories.
1109      *
1110      * @return  An array of strings naming the files and directories in the
1111      *          directory denoted by this abstract pathname.  The array will be
1112      *          empty if the directory is empty.  Returns {@code null} if
1113      *          this abstract pathname does not denote a directory, or if an
1114      *          I/O error occurs.
1115      *
1116      * @throws  SecurityException
1117      *          If a security manager exists and its {@link
1118      *          SecurityManager#checkRead(String)} method denies read access to
1119      *          the directory
1120      */
1121     public String[] list() {
1122         SecurityManager security = System.getSecurityManager();
1123         if (security != null) {
1124             security.checkRead(path);
1125         }
1126         if (isInvalid()) {
1127             return null;
1128         }
1129         return fs.list(this);
1130     }
1131 
1132     /**
1133      * Returns an array of strings naming the files and directories in the
1134      * directory denoted by this abstract pathname that satisfy the specified
1135      * filter.  The behavior of this method is the same as that of the
1136      * {@link #list()} method, except that the strings in the returned array
1137      * must satisfy the filter.  If the given {@code filter} is {@code null}
1138      * then all names are accepted.  Otherwise, a name satisfies the filter if
1139      * and only if the value {@code true} results when the {@link
1140      * FilenameFilter#accept FilenameFilter.accept(File,&nbsp;String)} method
1141      * of the filter is invoked on this abstract pathname and the name of a
1142      * file or directory in the directory that it denotes.
1143      *
1144      * @param  filter
1145      *         A filename filter
1146      *
1147      * @return  An array of strings naming the files and directories in the
1148      *          directory denoted by this abstract pathname that were accepted
1149      *          by the given {@code filter}.  The array will be empty if the
1150      *          directory is empty or if no names were accepted by the filter.
1151      *          Returns {@code null} if this abstract pathname does not denote
1152      *          a directory, or if an I/O error occurs.
1153      *
1154      * @throws  SecurityException
1155      *          If a security manager exists and its {@link
1156      *          SecurityManager#checkRead(String)} method denies read access to
1157      *          the directory
1158      *
1159      * @see java.nio.file.Files#newDirectoryStream(Path,String)
1160      */
1161     public String[] list(FilenameFilter filter) {
1162         String names[] = list();
1163         if ((names == null) || (filter == null)) {
1164             return names;
1165         }
1166         List<String> v = new ArrayList<>();
1167         for (int i = 0 ; i < names.length ; i++) {
1168             if (filter.accept(this, names[i])) {
1169                 v.add(names[i]);
1170             }
1171         }
1172         return v.toArray(new String[v.size()]);
1173     }
1174 
1175     /**
1176      * Returns an array of abstract pathnames denoting the files in the
1177      * directory denoted by this abstract pathname.
1178      *
1179      * <p> If this abstract pathname does not denote a directory, then this
1180      * method returns {@code null}.  Otherwise an array of {@code File} objects
1181      * is returned, one for each file or directory in the directory.  Pathnames
1182      * denoting the directory itself and the directory's parent directory are
1183      * not included in the result.  Each resulting abstract pathname is
1184      * constructed from this abstract pathname using the {@link #File(File,
1185      * String) File(File,&nbsp;String)} constructor.  Therefore if this
1186      * pathname is absolute then each resulting pathname is absolute; if this
1187      * pathname is relative then each resulting pathname will be relative to
1188      * the same directory.
1189      *
1190      * <p> There is no guarantee that the name strings in the resulting array
1191      * will appear in any specific order; they are not, in particular,
1192      * guaranteed to appear in alphabetical order.
1193      *
1194      * <p> Note that the {@link java.nio.file.Files} class defines the {@link
1195      * java.nio.file.Files#newDirectoryStream(Path) newDirectoryStream} method
1196      * to open a directory and iterate over the names of the files in the
1197      * directory. This may use less resources when working with very large
1198      * directories.
1199      *
1200      * @return  An array of abstract pathnames denoting the files and
1201      *          directories in the directory denoted by this abstract pathname.
1202      *          The array will be empty if the directory is empty.  Returns
1203      *          {@code null} if this abstract pathname does not denote a
1204      *          directory, or if an I/O error occurs.
1205      *
1206      * @throws  SecurityException
1207      *          If a security manager exists and its {@link
1208      *          SecurityManager#checkRead(String)} method denies read access to
1209      *          the directory
1210      *
1211      * @since  1.2
1212      */
1213     public File[] listFiles() {
1214         String[] ss = list();
1215         if (ss == null) return null;
1216         int n = ss.length;
1217         File[] fs = new File[n];
1218         for (int i = 0; i < n; i++) {
1219             fs[i] = new File(ss[i], this);
1220         }
1221         return fs;
1222     }
1223 
1224     /**
1225      * Returns an array of abstract pathnames denoting the files and
1226      * directories in the directory denoted by this abstract pathname that
1227      * satisfy the specified filter.  The behavior of this method is the same
1228      * as that of the {@link #listFiles()} method, except that the pathnames in
1229      * the returned array must satisfy the filter.  If the given {@code filter}
1230      * is {@code null} then all pathnames are accepted.  Otherwise, a pathname
1231      * satisfies the filter if and only if the value {@code true} results when
1232      * the {@link FilenameFilter#accept
1233      * FilenameFilter.accept(File,&nbsp;String)} method of the filter is
1234      * invoked on this abstract pathname and the name of a file or directory in
1235      * the directory that it denotes.
1236      *
1237      * @param  filter
1238      *         A filename filter
1239      *
1240      * @return  An array of abstract pathnames denoting the files and
1241      *          directories in the directory denoted by this abstract pathname.
1242      *          The array will be empty if the directory is empty.  Returns
1243      *          {@code null} if this abstract pathname does not denote a
1244      *          directory, or if an I/O error occurs.
1245      *
1246      * @throws  SecurityException
1247      *          If a security manager exists and its {@link
1248      *          SecurityManager#checkRead(String)} method denies read access to
1249      *          the directory
1250      *
1251      * @since  1.2
1252      * @see java.nio.file.Files#newDirectoryStream(Path,String)
1253      */
1254     public File[] listFiles(FilenameFilter filter) {
1255         String ss[] = list();
1256         if (ss == null) return null;
1257         ArrayList<File> files = new ArrayList<>();
1258         for (String s : ss)
1259             if ((filter == null) || filter.accept(this, s))
1260                 files.add(new File(s, this));
1261         return files.toArray(new File[files.size()]);
1262     }
1263 
1264     /**
1265      * Returns an array of abstract pathnames denoting the files and
1266      * directories in the directory denoted by this abstract pathname that
1267      * satisfy the specified filter.  The behavior of this method is the same
1268      * as that of the {@link #listFiles()} method, except that the pathnames in
1269      * the returned array must satisfy the filter.  If the given {@code filter}
1270      * is {@code null} then all pathnames are accepted.  Otherwise, a pathname
1271      * satisfies the filter if and only if the value {@code true} results when
1272      * the {@link FileFilter#accept FileFilter.accept(File)} method of the
1273      * filter is invoked on the pathname.
1274      *
1275      * @param  filter
1276      *         A file filter
1277      *
1278      * @return  An array of abstract pathnames denoting the files and
1279      *          directories in the directory denoted by this abstract pathname.
1280      *          The array will be empty if the directory is empty.  Returns
1281      *          {@code null} if this abstract pathname does not denote a
1282      *          directory, or if an I/O error occurs.
1283      *
1284      * @throws  SecurityException
1285      *          If a security manager exists and its {@link
1286      *          SecurityManager#checkRead(String)} method denies read access to
1287      *          the directory
1288      *
1289      * @since  1.2
1290      * @see java.nio.file.Files#newDirectoryStream(Path,java.nio.file.DirectoryStream.Filter)
1291      */
1292     public File[] listFiles(FileFilter filter) {
1293         String ss[] = list();
1294         if (ss == null) return null;
1295         ArrayList<File> files = new ArrayList<>();
1296         for (String s : ss) {
1297             File f = new File(s, this);
1298             if ((filter == null) || filter.accept(f))
1299                 files.add(f);
1300         }
1301         return files.toArray(new File[files.size()]);
1302     }
1303 
1304     /**
1305      * Creates the directory named by this abstract pathname.
1306      *
1307      * @return  <code>true</code> if and only if the directory was
1308      *          created; <code>false</code> otherwise
1309      *
1310      * @throws  SecurityException
1311      *          If a security manager exists and its {@link
1312      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1313      *          method does not permit the named directory to be created
1314      */
1315     public boolean mkdir() {
1316         SecurityManager security = System.getSecurityManager();
1317         if (security != null) {
1318             security.checkWrite(path);
1319         }
1320         if (isInvalid()) {
1321             return false;
1322         }
1323         return fs.createDirectory(this);
1324     }
1325 
1326     /**
1327      * Creates the directory named by this abstract pathname, including any
1328      * necessary but nonexistent parent directories.  Note that if this
1329      * operation fails it may have succeeded in creating some of the necessary
1330      * parent directories.
1331      *
1332      * @return  <code>true</code> if and only if the directory was created,
1333      *          along with all necessary parent directories; <code>false</code>
1334      *          otherwise
1335      *
1336      * @throws  SecurityException
1337      *          If a security manager exists and its {@link
1338      *          java.lang.SecurityManager#checkRead(java.lang.String)}
1339      *          method does not permit verification of the existence of the
1340      *          named directory and all necessary parent directories; or if
1341      *          the {@link
1342      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1343      *          method does not permit the named directory and all necessary
1344      *          parent directories to be created
1345      */
1346     public boolean mkdirs() {
1347         if (exists()) {
1348             return false;
1349         }
1350         if (mkdir()) {
1351             return true;
1352         }
1353         File canonFile = null;
1354         try {
1355             canonFile = getCanonicalFile();
1356         } catch (IOException e) {
1357             return false;
1358         }
1359 
1360         File parent = canonFile.getParentFile();
1361         return (parent != null && (parent.mkdirs() || parent.exists()) &&
1362                 canonFile.mkdir());
1363     }
1364 
1365     /**
1366      * Renames the file denoted by this abstract pathname.
1367      *
1368      * <p> Many aspects of the behavior of this method are inherently
1369      * platform-dependent: The rename operation might not be able to move a
1370      * file from one filesystem to another, it might not be atomic, and it
1371      * might not succeed if a file with the destination abstract pathname
1372      * already exists.  The return value should always be checked to make sure
1373      * that the rename operation was successful.
1374      *
1375      * <p> Note that the {@link java.nio.file.Files} class defines the {@link
1376      * java.nio.file.Files#move move} method to move or rename a file in a
1377      * platform independent manner.
1378      *
1379      * @param  dest  The new abstract pathname for the named file
1380      *
1381      * @return  <code>true</code> if and only if the renaming succeeded;
1382      *          <code>false</code> otherwise
1383      *
1384      * @throws  SecurityException
1385      *          If a security manager exists and its {@link
1386      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1387      *          method denies write access to either the old or new pathnames
1388      *
1389      * @throws  NullPointerException
1390      *          If parameter <code>dest</code> is <code>null</code>
1391      */
1392     public boolean renameTo(File dest) {
1393         SecurityManager security = System.getSecurityManager();
1394         if (security != null) {
1395             security.checkWrite(path);
1396             security.checkWrite(dest.path);
1397         }
1398         if (dest == null) {
1399             throw new NullPointerException();
1400         }
1401         if (this.isInvalid() || dest.isInvalid()) {
1402             return false;
1403         }
1404         return fs.rename(this, dest);
1405     }
1406 
1407     /**
1408      * Sets the last-modified time of the file or directory named by this
1409      * abstract pathname.
1410      *
1411      * <p> All platforms support file-modification times to the nearest second,
1412      * but some provide more precision.  The argument will be truncated to fit
1413      * the supported precision.  If the operation succeeds and no intervening
1414      * operations on the file take place, then the next invocation of the
1415      * {@link #lastModified} method will return the (possibly
1416      * truncated) <code>time</code> argument that was passed to this method.
1417      *
1418      * @param  time  The new last-modified time, measured in milliseconds since
1419      *               the epoch (00:00:00 GMT, January 1, 1970)
1420      *
1421      * @return <code>true</code> if and only if the operation succeeded;
1422      *          <code>false</code> otherwise
1423      *
1424      * @throws  IllegalArgumentException  If the argument is negative
1425      *
1426      * @throws  SecurityException
1427      *          If a security manager exists and its {@link
1428      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1429      *          method denies write access to the named file
1430      *
1431      * @since 1.2
1432      */
1433     public boolean setLastModified(long time) {
1434         if (time < 0) throw new IllegalArgumentException("Negative time");
1435         SecurityManager security = System.getSecurityManager();
1436         if (security != null) {
1437             security.checkWrite(path);
1438         }
1439         if (isInvalid()) {
1440             return false;
1441         }
1442         return fs.setLastModifiedTime(this, time);
1443     }
1444 
1445     /**
1446      * Marks the file or directory named by this abstract pathname so that
1447      * only read operations are allowed. After invoking this method the file
1448      * or directory will not change until it is either deleted or marked
1449      * to allow write access. On some platforms it may be possible to start the
1450      * Java virtual machine with special privileges that allow it to modify
1451      * files that are marked read-only. Whether or not a read-only file or
1452      * directory may be deleted depends upon the underlying system.
1453      *
1454      * @return <code>true</code> if and only if the operation succeeded;
1455      *          <code>false</code> otherwise
1456      *
1457      * @throws  SecurityException
1458      *          If a security manager exists and its {@link
1459      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1460      *          method denies write access to the named file
1461      *
1462      * @since 1.2
1463      */
1464     public boolean setReadOnly() {
1465         SecurityManager security = System.getSecurityManager();
1466         if (security != null) {
1467             security.checkWrite(path);
1468         }
1469         if (isInvalid()) {
1470             return false;
1471         }
1472         return fs.setReadOnly(this);
1473     }
1474 
1475     /**
1476      * Sets the owner's or everybody's write permission for this abstract
1477      * pathname. On some platforms it may be possible to start the Java virtual
1478      * machine with special privileges that allow it to modify files that
1479      * disallow write operations.
1480      *
1481      * <p> The {@link java.nio.file.Files} class defines methods that operate on
1482      * file attributes including file permissions. This may be used when finer
1483      * manipulation of file permissions is required.
1484      *
1485      * @param   writable
1486      *          If <code>true</code>, sets the access permission to allow write
1487      *          operations; if <code>false</code> to disallow write operations
1488      *
1489      * @param   ownerOnly
1490      *          If <code>true</code>, the write permission applies only to the
1491      *          owner's write permission; otherwise, it applies to everybody.  If
1492      *          the underlying file system can not distinguish the owner's write
1493      *          permission from that of others, then the permission will apply to
1494      *          everybody, regardless of this value.
1495      *
1496      * @return  <code>true</code> if and only if the operation succeeded. The
1497      *          operation will fail if the user does not have permission to change
1498      *          the access permissions of this abstract pathname.
1499      *
1500      * @throws  SecurityException
1501      *          If a security manager exists and its {@link
1502      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1503      *          method denies write access to the named file
1504      *
1505      * @since 1.6
1506      */
1507     public boolean setWritable(boolean writable, boolean ownerOnly) {
1508         SecurityManager security = System.getSecurityManager();
1509         if (security != null) {
1510             security.checkWrite(path);
1511         }
1512         if (isInvalid()) {
1513             return false;
1514         }
1515         return fs.setPermission(this, FileSystem.ACCESS_WRITE, writable, ownerOnly);
1516     }
1517 
1518     /**
1519      * A convenience method to set the owner's write permission for this abstract
1520      * pathname. On some platforms it may be possible to start the Java virtual
1521      * machine with special privileges that allow it to modify files that
1522      * disallow write operations.
1523      *
1524      * <p> An invocation of this method of the form {@code file.setWritable(arg)}
1525      * behaves in exactly the same way as the invocation
1526      *
1527      * <pre>{@code
1528      *     file.setWritable(arg, true)
1529      * }</pre>
1530      *
1531      * @param   writable
1532      *          If <code>true</code>, sets the access permission to allow write
1533      *          operations; if <code>false</code> to disallow write operations
1534      *
1535      * @return  <code>true</code> if and only if the operation succeeded.  The
1536      *          operation will fail if the user does not have permission to
1537      *          change the access permissions of this abstract pathname.
1538      *
1539      * @throws  SecurityException
1540      *          If a security manager exists and its {@link
1541      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1542      *          method denies write access to the file
1543      *
1544      * @since 1.6
1545      */
1546     public boolean setWritable(boolean writable) {
1547         return setWritable(writable, true);
1548     }
1549 
1550     /**
1551      * Sets the owner's or everybody's read permission for this abstract
1552      * pathname. On some platforms it may be possible to start the Java virtual
1553      * machine with special privileges that allow it to read files that are
1554      * marked as unreadable.
1555      *
1556      * <p> The {@link java.nio.file.Files} class defines methods that operate on
1557      * file attributes including file permissions. This may be used when finer
1558      * manipulation of file permissions is required.
1559      *
1560      * @param   readable
1561      *          If <code>true</code>, sets the access permission to allow read
1562      *          operations; if <code>false</code> to disallow read operations
1563      *
1564      * @param   ownerOnly
1565      *          If <code>true</code>, the read permission applies only to the
1566      *          owner's read permission; otherwise, it applies to everybody.  If
1567      *          the underlying file system can not distinguish the owner's read
1568      *          permission from that of others, then the permission will apply to
1569      *          everybody, regardless of this value.
1570      *
1571      * @return  <code>true</code> if and only if the operation succeeded.  The
1572      *          operation will fail if the user does not have permission to
1573      *          change the access permissions of this abstract pathname.  If
1574      *          <code>readable</code> is <code>false</code> and the underlying
1575      *          file system does not implement a read permission, then the
1576      *          operation will fail.
1577      *
1578      * @throws  SecurityException
1579      *          If a security manager exists and its {@link
1580      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1581      *          method denies write access to the file
1582      *
1583      * @since 1.6
1584      */
1585     public boolean setReadable(boolean readable, boolean ownerOnly) {
1586         SecurityManager security = System.getSecurityManager();
1587         if (security != null) {
1588             security.checkWrite(path);
1589         }
1590         if (isInvalid()) {
1591             return false;
1592         }
1593         return fs.setPermission(this, FileSystem.ACCESS_READ, readable, ownerOnly);
1594     }
1595 
1596     /**
1597      * A convenience method to set the owner's read permission for this abstract
1598      * pathname. On some platforms it may be possible to start the Java virtual
1599      * machine with special privileges that allow it to read files that are
1600      * marked as unreadable.
1601      *
1602      * <p>An invocation of this method of the form {@code file.setReadable(arg)}
1603      * behaves in exactly the same way as the invocation
1604      *
1605      * <pre>{@code
1606      *     file.setReadable(arg, true)
1607      * }</pre>
1608      *
1609      * @param  readable
1610      *          If <code>true</code>, sets the access permission to allow read
1611      *          operations; if <code>false</code> to disallow read operations
1612      *
1613      * @return  <code>true</code> if and only if the operation succeeded.  The
1614      *          operation will fail if the user does not have permission to
1615      *          change the access permissions of this abstract pathname.  If
1616      *          <code>readable</code> is <code>false</code> and the underlying
1617      *          file system does not implement a read permission, then the
1618      *          operation will fail.
1619      *
1620      * @throws  SecurityException
1621      *          If a security manager exists and its {@link
1622      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1623      *          method denies write access to the file
1624      *
1625      * @since 1.6
1626      */
1627     public boolean setReadable(boolean readable) {
1628         return setReadable(readable, true);
1629     }
1630 
1631     /**
1632      * Sets the owner's or everybody's execute permission for this abstract
1633      * pathname. On some platforms it may be possible to start the Java virtual
1634      * machine with special privileges that allow it to execute files that are
1635      * not marked executable.
1636      *
1637      * <p> The {@link java.nio.file.Files} class defines methods that operate on
1638      * file attributes including file permissions. This may be used when finer
1639      * manipulation of file permissions is required.
1640      *
1641      * @param   executable
1642      *          If <code>true</code>, sets the access permission to allow execute
1643      *          operations; if <code>false</code> to disallow execute operations
1644      *
1645      * @param   ownerOnly
1646      *          If <code>true</code>, the execute permission applies only to the
1647      *          owner's execute permission; otherwise, it applies to everybody.
1648      *          If the underlying file system can not distinguish the owner's
1649      *          execute permission from that of others, then the permission will
1650      *          apply to everybody, regardless of this value.
1651      *
1652      * @return  <code>true</code> if and only if the operation succeeded.  The
1653      *          operation will fail if the user does not have permission to
1654      *          change the access permissions of this abstract pathname.  If
1655      *          <code>executable</code> is <code>false</code> and the underlying
1656      *          file system does not implement an execute permission, then the
1657      *          operation will fail.
1658      *
1659      * @throws  SecurityException
1660      *          If a security manager exists and its {@link
1661      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1662      *          method denies write access to the file
1663      *
1664      * @since 1.6
1665      */
1666     public boolean setExecutable(boolean executable, boolean ownerOnly) {
1667         SecurityManager security = System.getSecurityManager();
1668         if (security != null) {
1669             security.checkWrite(path);
1670         }
1671         if (isInvalid()) {
1672             return false;
1673         }
1674         return fs.setPermission(this, FileSystem.ACCESS_EXECUTE, executable, ownerOnly);
1675     }
1676 
1677     /**
1678      * A convenience method to set the owner's execute permission for this
1679      * abstract pathname. On some platforms it may be possible to start the Java
1680      * virtual machine with special privileges that allow it to execute files
1681      * that are not marked executable.
1682      *
1683      * <p>An invocation of this method of the form {@code file.setExcutable(arg)}
1684      * behaves in exactly the same way as the invocation
1685      *
1686      * <pre>{@code
1687      *     file.setExecutable(arg, true)
1688      * }</pre>
1689      *
1690      * @param   executable
1691      *          If <code>true</code>, sets the access permission to allow execute
1692      *          operations; if <code>false</code> to disallow execute operations
1693      *
1694      * @return   <code>true</code> if and only if the operation succeeded.  The
1695      *           operation will fail if the user does not have permission to
1696      *           change the access permissions of this abstract pathname.  If
1697      *           <code>executable</code> is <code>false</code> and the underlying
1698      *           file system does not implement an execute permission, then the
1699      *           operation will fail.
1700      *
1701      * @throws  SecurityException
1702      *          If a security manager exists and its {@link
1703      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
1704      *          method denies write access to the file
1705      *
1706      * @since 1.6
1707      */
1708     public boolean setExecutable(boolean executable) {
1709         return setExecutable(executable, true);
1710     }
1711 
1712     /**
1713      * Tests whether the application can execute the file denoted by this
1714      * abstract pathname. On some platforms it may be possible to start the
1715      * Java virtual machine with special privileges that allow it to execute
1716      * files that are not marked executable. Consequently this method may return
1717      * {@code true} even though the file does not have execute permissions.
1718      *
1719      * @return  <code>true</code> if and only if the abstract pathname exists
1720      *          <em>and</em> the application is allowed to execute the file
1721      *
1722      * @throws  SecurityException
1723      *          If a security manager exists and its {@link
1724      *          java.lang.SecurityManager#checkExec(java.lang.String)}
1725      *          method denies execute access to the file
1726      *
1727      * @since 1.6
1728      */
1729     public boolean canExecute() {
1730         SecurityManager security = System.getSecurityManager();
1731         if (security != null) {
1732             security.checkExec(path);
1733         }
1734         if (isInvalid()) {
1735             return false;
1736         }
1737         return fs.checkAccess(this, FileSystem.ACCESS_EXECUTE);
1738     }
1739 
1740 
1741     /* -- Filesystem interface -- */
1742 
1743     /**
1744      * List the available filesystem roots.
1745      *
1746      * <p> A particular Java platform may support zero or more
1747      * hierarchically-organized file systems.  Each file system has a
1748      * {@code root} directory from which all other files in that file system
1749      * can be reached.  Windows platforms, for example, have a root directory
1750      * for each active drive; UNIX platforms have a single root directory,
1751      * namely {@code "/"}.  The set of available filesystem roots is affected
1752      * by various system-level operations such as the insertion or ejection of
1753      * removable media and the disconnecting or unmounting of physical or
1754      * virtual disk drives.
1755      *
1756      * <p> This method returns an array of {@code File} objects that denote the
1757      * root directories of the available filesystem roots.  It is guaranteed
1758      * that the canonical pathname of any file physically present on the local
1759      * machine will begin with one of the roots returned by this method.
1760      *
1761      * <p> The canonical pathname of a file that resides on some other machine
1762      * and is accessed via a remote-filesystem protocol such as SMB or NFS may
1763      * or may not begin with one of the roots returned by this method.  If the
1764      * pathname of a remote file is syntactically indistinguishable from the
1765      * pathname of a local file then it will begin with one of the roots
1766      * returned by this method.  Thus, for example, {@code File} objects
1767      * denoting the root directories of the mapped network drives of a Windows
1768      * platform will be returned by this method, while {@code File} objects
1769      * containing UNC pathnames will not be returned by this method.
1770      *
1771      * <p> Unlike most methods in this class, this method does not throw
1772      * security exceptions.  If a security manager exists and its {@link
1773      * SecurityManager#checkRead(String)} method denies read access to a
1774      * particular root directory, then that directory will not appear in the
1775      * result.
1776      *
1777      * @return  An array of {@code File} objects denoting the available
1778      *          filesystem roots, or {@code null} if the set of roots could not
1779      *          be determined.  The array will be empty if there are no
1780      *          filesystem roots.
1781      *
1782      * @since  1.2
1783      * @see java.nio.file.FileStore
1784      */
1785     public static File[] listRoots() {
1786         return fs.listRoots();
1787     }
1788 
1789 
1790     /* -- Disk usage -- */
1791 
1792     /**
1793      * Returns the size of the partition <a href="#partName">named</a> by this
1794      * abstract pathname.
1795      *
1796      * @return  The size, in bytes, of the partition or {@code 0L} if this
1797      *          abstract pathname does not name a partition
1798      *
1799      * @throws  SecurityException
1800      *          If a security manager has been installed and it denies
1801      *          {@link RuntimePermission}{@code ("getFileSystemAttributes")}
1802      *          or its {@link SecurityManager#checkRead(String)} method denies
1803      *          read access to the file named by this abstract pathname
1804      *
1805      * @since  1.6
1806      */
1807     public long getTotalSpace() {
1808         SecurityManager sm = System.getSecurityManager();
1809         if (sm != null) {
1810             sm.checkPermission(new RuntimePermission("getFileSystemAttributes"));
1811             sm.checkRead(path);
1812         }
1813         if (isInvalid()) {
1814             return 0L;
1815         }
1816         return fs.getSpace(this, FileSystem.SPACE_TOTAL);
1817     }
1818 
1819     /**
1820      * Returns the number of unallocated bytes in the partition <a
1821      * href="#partName">named</a> by this abstract path name.
1822      *
1823      * <p> The returned number of unallocated bytes is a hint, but not
1824      * a guarantee, that it is possible to use most or any of these
1825      * bytes.  The number of unallocated bytes is most likely to be
1826      * accurate immediately after this call.  It is likely to be made
1827      * inaccurate by any external I/O operations including those made
1828      * on the system outside of this virtual machine.  This method
1829      * makes no guarantee that write operations to this file system
1830      * will succeed.
1831      *
1832      * @return  The number of unallocated bytes on the partition or {@code 0L}
1833      *          if the abstract pathname does not name a partition.  This
1834      *          value will be less than or equal to the total file system size
1835      *          returned by {@link #getTotalSpace}.
1836      *
1837      * @throws  SecurityException
1838      *          If a security manager has been installed and it denies
1839      *          {@link RuntimePermission}{@code ("getFileSystemAttributes")}
1840      *          or its {@link SecurityManager#checkRead(String)} method denies
1841      *          read access to the file named by this abstract pathname
1842      *
1843      * @since  1.6
1844      */
1845     public long getFreeSpace() {
1846         SecurityManager sm = System.getSecurityManager();
1847         if (sm != null) {
1848             sm.checkPermission(new RuntimePermission("getFileSystemAttributes"));
1849             sm.checkRead(path);
1850         }
1851         if (isInvalid()) {
1852             return 0L;
1853         }
1854         return fs.getSpace(this, FileSystem.SPACE_FREE);
1855     }
1856 
1857     /**
1858      * Returns the number of bytes available to this virtual machine on the
1859      * partition <a href="#partName">named</a> by this abstract pathname.  When
1860      * possible, this method checks for write permissions and other operating
1861      * system restrictions and will therefore usually provide a more accurate
1862      * estimate of how much new data can actually be written than {@link
1863      * #getFreeSpace}.
1864      *
1865      * <p> The returned number of available bytes is a hint, but not a
1866      * guarantee, that it is possible to use most or any of these bytes.  The
1867      * number of unallocated bytes is most likely to be accurate immediately
1868      * after this call.  It is likely to be made inaccurate by any external
1869      * I/O operations including those made on the system outside of this
1870      * virtual machine.  This method makes no guarantee that write operations
1871      * to this file system will succeed.
1872      *
1873      * @return  The number of available bytes on the partition or {@code 0L}
1874      *          if the abstract pathname does not name a partition.  On
1875      *          systems where this information is not available, this method
1876      *          will be equivalent to a call to {@link #getFreeSpace}.
1877      *
1878      * @throws  SecurityException
1879      *          If a security manager has been installed and it denies
1880      *          {@link RuntimePermission}{@code ("getFileSystemAttributes")}
1881      *          or its {@link SecurityManager#checkRead(String)} method denies
1882      *          read access to the file named by this abstract pathname
1883      *
1884      * @since  1.6
1885      */
1886     public long getUsableSpace() {
1887         SecurityManager sm = System.getSecurityManager();
1888         if (sm != null) {
1889             sm.checkPermission(new RuntimePermission("getFileSystemAttributes"));
1890             sm.checkRead(path);
1891         }
1892         if (isInvalid()) {
1893             return 0L;
1894         }
1895         return fs.getSpace(this, FileSystem.SPACE_USABLE);
1896     }
1897 
1898     /* -- Temporary files -- */
1899 
1900     private static class TempDirectory {
1901         private TempDirectory() { }
1902 
1903         // temporary directory location
1904         private static final File tmpdir = new File(
1905                 GetPropertyAction.privilegedGetProperty("java.io.tmpdir"));
1906         static File location() {
1907             return tmpdir;
1908         }
1909 
1910         // file name generation
1911         private static final SecureRandom random = new SecureRandom();
1912         private static int shortenSubName(int subNameLength, int excess,
1913             int nameMin) {
1914             int newLength = Math.max(nameMin, subNameLength - excess);
1915             if (newLength < subNameLength) {
1916                 return newLength;
1917             }
1918             return subNameLength;
1919         }
1920         static File generateFile(String prefix, String suffix, File dir)
1921             throws IOException
1922         {
1923             long n = random.nextLong();
1924             String nus = Long.toUnsignedString(n);
1925 
1926             // Use only the file name from the supplied prefix
1927             prefix = (new File(prefix)).getName();
1928 
1929             int prefixLength = prefix.length();
1930             int nusLength = nus.length();
1931             int suffixLength = suffix.length();;
1932 
1933             String name;
1934             int nameMax = fs.getNameMax(dir.getPath());
1935             int excess = prefixLength + nusLength + suffixLength - nameMax;
1936             if (excess <= 0) {
1937                 name = prefix + nus + suffix;
1938             } else {
1939                 // Name exceeds the maximum path component length: shorten it
1940 
1941                 // Attempt to shorten the prefix length to no less then 3
1942                 prefixLength = shortenSubName(prefixLength, excess, 3);
1943                 excess = prefixLength + nusLength + suffixLength - nameMax;
1944 
1945                 if (excess > 0) {
1946                     // Attempt to shorten the suffix length to no less than
1947                     // 0 or 4 depending on whether it begins with a dot ('.')
1948                     suffixLength = shortenSubName(suffixLength, excess,
1949                         suffix.indexOf(".") == 0 ? 4 : 0);
1950                     suffixLength = shortenSubName(suffixLength, excess, 3);
1951                     excess = prefixLength + nusLength + suffixLength - nameMax;
1952                 }
1953 
1954                 if (excess > 0 && excess <= nusLength - 5) {
1955                     // Attempt to shorten the random character string length
1956                     // to no less than 5
1957                     nusLength = shortenSubName(nusLength, excess, 5);
1958                 }
1959 
1960                 StringBuilder sb =
1961                     new StringBuilder(prefixLength + nusLength + suffixLength);
1962                 sb.append(prefixLength < prefix.length() ?
1963                     prefix.substring(0, prefixLength) : prefix);
1964                 sb.append(nusLength < nus.length() ?
1965                     nus.substring(0, nusLength) : nus);
1966                 sb.append(suffixLength < suffix.length() ?
1967                     suffix.substring(0, suffixLength) : suffix);
1968                 name = sb.toString();
1969             }
1970 
1971             // Normalize the path component
1972             name = fs.normalize(name);
1973 
1974             File f = new File(dir, name);
1975             if (!name.equals(f.getName()) || f.isInvalid()) {
1976                 if (System.getSecurityManager() != null)
1977                     throw new IOException("Unable to create temporary file");
1978                 else
1979                     throw new IOException("Unable to create temporary file, "
1980                         + name);
1981             }
1982             return f;
1983         }
1984     }
1985 
1986     /**
1987      * <p> Creates a new empty file in the specified directory, using the
1988      * given prefix and suffix strings to generate its name.  If this method
1989      * returns successfully then it is guaranteed that:
1990      *
1991      * <ol>
1992      * <li> The file denoted by the returned abstract pathname did not exist
1993      *      before this method was invoked, and
1994      * <li> Neither this method nor any of its variants will return the same
1995      *      abstract pathname again in the current invocation of the virtual
1996      *      machine.
1997      * </ol>
1998      *
1999      * This method provides only part of a temporary-file facility.  To arrange
2000      * for a file created by this method to be deleted automatically, use the
2001      * {@link #deleteOnExit} method.
2002      *
2003      * <p> The <code>prefix</code> argument must be at least three characters
2004      * long.  It is recommended that the prefix be a short, meaningful string
2005      * such as <code>"hjb"</code> or <code>"mail"</code>.  The
2006      * <code>suffix</code> argument may be <code>null</code>, in which case the
2007      * suffix <code>".tmp"</code> will be used.
2008      *
2009      * <p> To create the new file, the prefix and the suffix may first be
2010      * adjusted to fit the limitations of the underlying platform.  If the
2011      * prefix is too long then it will be truncated, but its first three
2012      * characters will always be preserved.  If the suffix is too long then it
2013      * too will be truncated, but if it begins with a period character
2014      * (<code>'.'</code>) then the period and the first three characters
2015      * following it will always be preserved.  Once these adjustments have been
2016      * made the name of the new file will be generated by concatenating the
2017      * prefix, five or more internally-generated characters, and the suffix.
2018      *
2019      * <p> If the <code>directory</code> argument is <code>null</code> then the
2020      * system-dependent default temporary-file directory will be used.  The
2021      * default temporary-file directory is specified by the system property
2022      * <code>java.io.tmpdir</code>.  On UNIX systems the default value of this
2023      * property is typically <code>"/tmp"</code> or <code>"/var/tmp"</code>; on
2024      * Microsoft Windows systems it is typically <code>"C:\\WINNT\\TEMP"</code>.  A different
2025      * value may be given to this system property when the Java virtual machine
2026      * is invoked, but programmatic changes to this property are not guaranteed
2027      * to have any effect upon the temporary directory used by this method.
2028      *
2029      * @param  prefix     The prefix string to be used in generating the file's
2030      *                    name; must be at least three characters long
2031      *
2032      * @param  suffix     The suffix string to be used in generating the file's
2033      *                    name; may be <code>null</code>, in which case the
2034      *                    suffix <code>".tmp"</code> will be used
2035      *
2036      * @param  directory  The directory in which the file is to be created, or
2037      *                    <code>null</code> if the default temporary-file
2038      *                    directory is to be used
2039      *
2040      * @return  An abstract pathname denoting a newly-created empty file
2041      *
2042      * @throws  IllegalArgumentException
2043      *          If the <code>prefix</code> argument contains fewer than three
2044      *          characters
2045      *
2046      * @throws  IOException  If a file could not be created
2047      *
2048      * @throws  SecurityException
2049      *          If a security manager exists and its {@link
2050      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
2051      *          method does not allow a file to be created
2052      *
2053      * @since 1.2
2054      */
2055     public static File createTempFile(String prefix, String suffix,
2056                                       File directory)
2057         throws IOException
2058     {
2059         if (prefix.length() < 3) {
2060             throw new IllegalArgumentException("Prefix string \"" + prefix +
2061                 "\" too short: length must be at least 3");
2062         }
2063         if (suffix == null)
2064             suffix = ".tmp";
2065 
2066         File tmpdir = (directory != null) ? directory
2067                                           : TempDirectory.location();
2068         SecurityManager sm = System.getSecurityManager();
2069         File f;
2070         do {
2071             f = TempDirectory.generateFile(prefix, suffix, tmpdir);
2072 
2073             if (sm != null) {
2074                 try {
2075                     sm.checkWrite(f.getPath());
2076                 } catch (SecurityException se) {
2077                     // don't reveal temporary directory location
2078                     if (directory == null)
2079                         throw new SecurityException("Unable to create temporary file");
2080                     throw se;
2081                 }
2082             }
2083         } while ((fs.getBooleanAttributes(f) & FileSystem.BA_EXISTS) != 0);
2084 
2085         if (!fs.createFileExclusively(f.getPath()))
2086             throw new IOException("Unable to create temporary file");
2087 
2088         return f;
2089     }
2090 
2091     /**
2092      * Creates an empty file in the default temporary-file directory, using
2093      * the given prefix and suffix to generate its name. Invoking this method
2094      * is equivalent to invoking {@link #createTempFile(java.lang.String,
2095      * java.lang.String, java.io.File)
2096      * createTempFile(prefix,&nbsp;suffix,&nbsp;null)}.
2097      *
2098      * <p> The {@link
2099      * java.nio.file.Files#createTempFile(String,String,java.nio.file.attribute.FileAttribute[])
2100      * Files.createTempFile} method provides an alternative method to create an
2101      * empty file in the temporary-file directory. Files created by that method
2102      * may have more restrictive access permissions to files created by this
2103      * method and so may be more suited to security-sensitive applications.
2104      *
2105      * @param  prefix     The prefix string to be used in generating the file's
2106      *                    name; must be at least three characters long
2107      *
2108      * @param  suffix     The suffix string to be used in generating the file's
2109      *                    name; may be <code>null</code>, in which case the
2110      *                    suffix <code>".tmp"</code> will be used
2111      *
2112      * @return  An abstract pathname denoting a newly-created empty file
2113      *
2114      * @throws  IllegalArgumentException
2115      *          If the <code>prefix</code> argument contains fewer than three
2116      *          characters
2117      *
2118      * @throws  IOException  If a file could not be created
2119      *
2120      * @throws  SecurityException
2121      *          If a security manager exists and its {@link
2122      *          java.lang.SecurityManager#checkWrite(java.lang.String)}
2123      *          method does not allow a file to be created
2124      *
2125      * @since 1.2
2126      * @see java.nio.file.Files#createTempDirectory(String,FileAttribute[])
2127      */
2128     public static File createTempFile(String prefix, String suffix)
2129         throws IOException
2130     {
2131         return createTempFile(prefix, suffix, null);
2132     }
2133 
2134     /* -- Basic infrastructure -- */
2135 
2136     /**
2137      * Compares two abstract pathnames lexicographically.  The ordering
2138      * defined by this method depends upon the underlying system.  On UNIX
2139      * systems, alphabetic case is significant in comparing pathnames; on Microsoft Windows
2140      * systems it is not.
2141      *
2142      * @param   pathname  The abstract pathname to be compared to this abstract
2143      *                    pathname
2144      *
2145      * @return  Zero if the argument is equal to this abstract pathname, a
2146      *          value less than zero if this abstract pathname is
2147      *          lexicographically less than the argument, or a value greater
2148      *          than zero if this abstract pathname is lexicographically
2149      *          greater than the argument
2150      *
2151      * @since   1.2
2152      */
2153     public int compareTo(File pathname) {
2154         return fs.compare(this, pathname);
2155     }
2156 
2157     /**
2158      * Tests this abstract pathname for equality with the given object.
2159      * Returns <code>true</code> if and only if the argument is not
2160      * <code>null</code> and is an abstract pathname that denotes the same file
2161      * or directory as this abstract pathname.  Whether or not two abstract
2162      * pathnames are equal depends upon the underlying system.  On UNIX
2163      * systems, alphabetic case is significant in comparing pathnames; on Microsoft Windows
2164      * systems it is not.
2165      *
2166      * @param   obj   The object to be compared with this abstract pathname
2167      *
2168      * @return  <code>true</code> if and only if the objects are the same;
2169      *          <code>false</code> otherwise
2170      */
2171     public boolean equals(Object obj) {
2172         if ((obj != null) && (obj instanceof File)) {
2173             return compareTo((File)obj) == 0;
2174         }
2175         return false;
2176     }
2177 
2178     /**
2179      * Computes a hash code for this abstract pathname.  Because equality of
2180      * abstract pathnames is inherently system-dependent, so is the computation
2181      * of their hash codes.  On UNIX systems, the hash code of an abstract
2182      * pathname is equal to the exclusive <em>or</em> of the hash code
2183      * of its pathname string and the decimal value
2184      * <code>1234321</code>.  On Microsoft Windows systems, the hash
2185      * code is equal to the exclusive <em>or</em> of the hash code of
2186      * its pathname string converted to lower case and the decimal
2187      * value <code>1234321</code>.  Locale is not taken into account on
2188      * lowercasing the pathname string.
2189      *
2190      * @return  A hash code for this abstract pathname
2191      */
2192     public int hashCode() {
2193         return fs.hashCode(this);
2194     }
2195 
2196     /**
2197      * Returns the pathname string of this abstract pathname.  This is just the
2198      * string returned by the {@link #getPath} method.
2199      *
2200      * @return  The string form of this abstract pathname
2201      */
2202     public String toString() {
2203         return getPath();
2204     }
2205 
2206     /**
2207      * WriteObject is called to save this filename.
2208      * The separator character is saved also so it can be replaced
2209      * in case the path is reconstituted on a different host type.
2210      *
2211      * @serialData  Default fields followed by separator character.
2212      */
2213     private synchronized void writeObject(java.io.ObjectOutputStream s)
2214         throws IOException
2215     {
2216         s.defaultWriteObject();
2217         s.writeChar(separatorChar); // Add the separator character
2218     }
2219 
2220     /**
2221      * readObject is called to restore this filename.
2222      * The original separator character is read.  If it is different
2223      * than the separator character on this system, then the old separator
2224      * is replaced by the local separator.
2225      */
2226     private synchronized void readObject(java.io.ObjectInputStream s)
2227          throws IOException, ClassNotFoundException
2228     {
2229         ObjectInputStream.GetField fields = s.readFields();
2230         String pathField = (String)fields.get("path", null);
2231         char sep = s.readChar(); // read the previous separator char
2232         if (sep != separatorChar)
2233             pathField = pathField.replace(sep, separatorChar);
2234         String path = fs.normalize(pathField);
2235         UNSAFE.putObject(this, PATH_OFFSET, path);
2236         UNSAFE.putIntVolatile(this, PREFIX_LENGTH_OFFSET, fs.prefixLength(path));
2237     }
2238 
2239     private static final long PATH_OFFSET;
2240     private static final long PREFIX_LENGTH_OFFSET;
2241     private static final jdk.internal.misc.Unsafe UNSAFE;
2242     static {
2243         try {
2244             jdk.internal.misc.Unsafe unsafe = jdk.internal.misc.Unsafe.getUnsafe();
2245             PATH_OFFSET = unsafe.objectFieldOffset(
2246                     File.class.getDeclaredField("path"));
2247             PREFIX_LENGTH_OFFSET = unsafe.objectFieldOffset(
2248                     File.class.getDeclaredField("prefixLength"));
2249             UNSAFE = unsafe;
2250         } catch (ReflectiveOperationException e) {
2251             throw new Error(e);
2252         }
2253     }
2254 
2255 
2256     /** use serialVersionUID from JDK 1.0.2 for interoperability */
2257     private static final long serialVersionUID = 301077366599181567L;
2258 
2259     // -- Integration with java.nio.file --
2260 
2261     private transient volatile Path filePath;
2262 
2263     /**
2264      * Returns a {@link Path java.nio.file.Path} object constructed from the
2265      * this abstract path. The resulting {@code Path} is associated with the
2266      * {@link java.nio.file.FileSystems#getDefault default-filesystem}.
2267      *
2268      * <p> The first invocation of this method works as if invoking it were
2269      * equivalent to evaluating the expression:
2270      * <blockquote><pre>
2271      * {@link java.nio.file.FileSystems#getDefault FileSystems.getDefault}().{@link
2272      * java.nio.file.FileSystem#getPath getPath}(this.{@link #getPath getPath}());
2273      * </pre></blockquote>
2274      * Subsequent invocations of this method return the same {@code Path}.
2275      *
2276      * <p> If this abstract pathname is the empty abstract pathname then this
2277      * method returns a {@code Path} that may be used to access the current
2278      * user directory.
2279      *
2280      * @return  a {@code Path} constructed from this abstract path
2281      *
2282      * @throws  java.nio.file.InvalidPathException
2283      *          if a {@code Path} object cannot be constructed from the abstract
2284      *          path (see {@link java.nio.file.FileSystem#getPath FileSystem.getPath})
2285      *
2286      * @since   1.7
2287      * @see Path#toFile
2288      */
2289     public Path toPath() {
2290         Path result = filePath;
2291         if (result == null) {
2292             synchronized (this) {
2293                 result = filePath;
2294                 if (result == null) {
2295                     result = FileSystems.getDefault().getPath(path);
2296                     filePath = result;
2297                 }
2298             }
2299         }
2300         return result;
2301     }
2302 }