View Javadoc
1   /*
2    * Copyright (c) 1994, 2013, 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
22   * or visit www.oracle.com if you need additional information or have any
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.AccessController;
35  import java.security.SecureRandom;
36  import java.nio.file.Path;
37  import java.nio.file.FileSystems;
38  import sun.security.action.GetPropertyAction;
39  
40  /**
41   * An abstract representation of file and directory pathnames.
42   *
43   * <p> User interfaces and operating systems use system-dependent <em>pathname
44   * strings</em> to name files and directories.  This class presents an
45   * abstract, system-independent view of hierarchical pathnames.  An
46   * <em>abstract pathname</em> has two components:
47   *
48   * <ol>
49   * <li> An optional system-dependent <em>prefix</em> string,
50   *      such as a disk-drive specifier, <code>"/"</code>&nbsp;for the UNIX root
51   *      directory, or <code>"\\\\"</code>&nbsp;for a Microsoft Windows UNC pathname, and
52   * <li> A sequence of zero or more string <em>names</em>.
53   * </ol>
54   *
55   * The first name in an abstract pathname may be a directory name or, in the
56   * case of Microsoft Windows UNC pathnames, a hostname.  Each subsequent name
57   * in an abstract pathname denotes a directory; the last name may denote
58   * either a directory or a file.  The <em>empty</em> abstract pathname has no
59   * prefix and an empty name sequence.
60   *
61   * <p> The conversion of a pathname string to or from an abstract pathname is
62   * inherently system-dependent.  When an abstract pathname is converted into a
63   * pathname string, each name is separated from the next by a single copy of
64   * the default <em>separator character</em>.  The default name-separator
65   * character is defined by the system property <code>file.separator</code>, and
66   * is made available in the public static fields <code>{@link
67   * #separator}</code> and <code>{@link #separatorChar}</code> of this class.
68   * When a pathname string is converted into an abstract pathname, the names
69   * within it may be separated by the default name-separator character or by any
70   * other name-separator character that is supported by the underlying system.
71   *
72   * <p> A pathname, whether abstract or in string form, may be either
73   * <em>absolute</em> or <em>relative</em>.  An absolute pathname is complete in
74   * that no other information is required in order to locate the file that it
75   * denotes.  A relative pathname, in contrast, must be interpreted in terms of
76   * information taken from some other pathname.  By default the classes in the
77   * <code>java.io</code> package always resolve relative pathnames against the
78   * current user directory.  This directory is named by the system property
79   * <code>user.dir</code>, and is typically the directory in which the Java
80   * virtual machine was invoked.
81   *
82   * <p> The <em>parent</em> of an abstract pathname may be obtained by invoking
83   * the {@link #getParent} method of this class and consists of the pathname's
84   * prefix and each name in the pathname's name sequence except for the last.
85   * Each directory's absolute pathname is an ancestor of any <tt>File</tt>
86   * object with an absolute abstract pathname which begins with the directory's
87   * absolute pathname.  For example, the directory denoted by the abstract
88   * pathname <tt>"/usr"</tt> is an ancestor of the directory denoted by the
89   * pathname <tt>"/usr/local/bin"</tt>.
90   *
91   * <p> The prefix concept is used to handle root directories on UNIX platforms,
92   * and drive specifiers, root directories and UNC pathnames on Microsoft Windows platforms,
93   * as follows:
94   *
95   * <ul>
96   *
97   * <li> For UNIX platforms, the prefix of an absolute pathname is always
98   * <code>"/"</code>.  Relative pathnames have no prefix.  The abstract pathname
99   * denoting the root directory has the prefix <code>"/"</code> and an empty
100  * name sequence.
101  *
102  * <li> For Microsoft Windows platforms, the prefix of a pathname that contains a drive
103  * specifier consists of the drive letter followed by <code>":"</code> and
104  * possibly followed by <code>"\\"</code> if the pathname is absolute.  The
105  * prefix of a UNC pathname is <code>"\\\\"</code>; the hostname and the share
106  * name are the first two names in the name sequence.  A relative pathname that
107  * does not specify a drive has no prefix.
108  *
109  * </ul>
110  *
111  * <p> Instances of this class may or may not denote an actual file-system
112  * object such as a file or a directory.  If it does denote such an object
113  * then that object resides in a <i>partition</i>.  A partition is an
114  * operating system-specific portion of storage for a file system.  A single
115  * storage device (e.g. a physical disk-drive, flash memory, CD-ROM) may
116  * contain multiple partitions.  The object, if any, will reside on the
117  * partition <a name="partName">named</a> by some ancestor of the absolute
118  * form of this pathname.
119  *
120  * <p> A file system may implement restrictions to certain operations on the
121  * actual file-system object, such as reading, writing, and executing.  These
122  * restrictions are collectively known as <i>access permissions</i>.  The file
123  * system may have multiple sets of access permissions on a single object.
124  * For example, one set may apply to the object's <i>owner</i>, and another
125  * may apply to all other users.  The access permissions on an object may
126  * cause some methods in this class to fail.
127  *
128  * <p> Instances of the <code>File</code> class are immutable; that is, once
129  * created, the abstract pathname represented by a <code>File</code> object
130  * will never change.
131  *
132  * <h3>Interoperability with {@code java.nio.file} package</h3>
133  *
134  * <p> The <a href="../../java/nio/file/package-summary.html">{@code java.nio.file}</a>
135  * package defines interfaces and classes for the Java virtual machine to access
136  * files, file attributes, and file systems. This API may be used to overcome
137  * many of the limitations of the {@code java.io.File} class.
138  * The {@link #toPath toPath} method may be used to obtain a {@link
139  * Path} that uses the abstract path represented by a {@code File} object to
140  * locate a file. The resulting {@code Path} may be used with the {@link
141  * java.nio.file.Files} class to provide more efficient and extensive access to
142  * additional file operations, file attributes, and I/O exceptions to help
143  * diagnose errors when an operation on a file fails.
144  *
145  * @author  unascribed
146  * @since   JDK1.0
147  */
148 
149 public class File
150     implements Serializable, Comparable<File>
151 {
152 
153     /**
154      * The FileSystem object representing the platform's local file system.
155      */
156     private static final FileSystem fs = DefaultFileSystem.getFileSystem();
157 
158     /**
159      * This abstract pathname's normalized pathname string. A normalized
160      * pathname string uses the default name-separator character and does not
161      * contain any duplicate or redundant separators.
162      *
163      * @serial
164      */
165     private final String path;
166 
167     /**
168      * Enum type that indicates the status of a file path.
169      */
170     private static enum PathStatus { INVALID, CHECKED };
171 
172     /**
173      * The flag indicating whether the file path is invalid.
174      */
175     private transient PathStatus status = null;
176 
177     /**
178      * Check if the file has an invalid path. Currently, the inspection of
179      * a file path is very limited, and it only covers Nul character check.
180      * Returning true means the path is definitely invalid/garbage. But
181      * returning false does not guarantee that the path is valid.
182      *
183      * @return true if the file path is invalid.
184      */
185     final boolean isInvalid() {
186         if (status == null) {
187             status = (this.path.indexOf('\u0000') < 0) ? PathStatus.CHECKED
188                                                        : PathStatus.INVALID;
189         }
190         return status == PathStatus.INVALID;
191     }
192 
193     /**
194      * The length of this abstract pathname's prefix, or zero if it has no
195      * prefix.
196      */
197     private final transient int prefixLength;
198 
199     /**
200      * Returns the length of this abstract pathname's prefix.
201      * For use by FileSystem classes.
202      */
203     int getPrefixLength() {
204         return prefixLength;
205     }
206 
207     /**
208      * The system-dependent default name-separator character.  This field is
209      * initialized to contain the first character of the value of the system
210      * property <code>file.separator</code>.  On UNIX systems the value of this
211      * field is <code>'/'</code>; on Microsoft Windows systems it is <code>'\\'</code>.
212      *
213      * @see     java.lang.System#getProperty(java.lang.String)
214      */
215     public static final char separatorChar = fs.getSeparator();
216 
217     /**
218      * The system-dependent default name-separator character, represented as a
219      * string for convenience.  This string contains a single character, namely
220      * <code>{@link #separatorChar}</code>.
221      */
222     public static final String separator = "" + separatorChar;
223 
224     /**
225      * The system-dependent path-separator character.  This field is
226      * initialized to contain the first character of the value of the system
227      * property <code>path.separator</code>.  This character is used to
228      * separate filenames in a sequence of files given as a <em>path list</em>.
229      * On UNIX systems, this character is <code>':'</code>; on Microsoft Windows systems it
230      * is <code>';'</code>.
231      *
232      * @see     java.lang.System#getProperty(java.lang.String)
233      */
234     public static final char pathSeparatorChar = fs.getPathSeparator();
235 
236     /**
237      * The system-dependent path-separator character, represented as a string
238      * for convenience.  This string contains a single character, namely
239      * <code>{@link #pathSeparatorChar}</code>.
240      */
241     public static final String pathSeparator = "" + pathSeparatorChar;
242 
243 
244     /* -- Constructors -- */
245 
246     /**
247      * Internal constructor for already-normalized pathname strings.
248      */
249     private File(String pathname, int prefixLength) {
250         this.path = pathname;
251         this.prefixLength = prefixLength;
252     }
253 
254     /**
255      * Internal constructor for already-normalized pathname strings.
256      * The parameter order is used to disambiguate this method from the
257      * public(File, String) constructor.
258      */
259     private File(String child, File parent) {
260         assert parent.path != null;
261         assert (!parent.path.equals(""));
262         this.path = fs.resolve(parent.path, child);
263         this.prefixLength = parent.prefixLength;
264     }
265 
266     /**
267      * Creates a new <code>File</code> instance by converting the given
268      * pathname string into an abstract pathname.  If the given string is
269      * the empty string, then the result is the empty abstract pathname.
270      *
271      * @param   pathname  A pathname string
272      * @throws  NullPointerException
273      *          If the <code>pathname</code> argument is <code>null</code>
274      */
275     public File(String pathname) {
276         if (pathname == null) {
277             throw new NullPointerException();
278         }
279         this.path = fs.normalize(pathname);
280         this.prefixLength = fs.prefixLength(this.path);
281     }
282 
283     /* Note: The two-argument File constructors do not interpret an empty
284        parent abstract pathname as the current user directory.  An empty parent
285        instead causes the child to be resolved against the system-dependent
286        directory defined by the FileSystem.getDefaultParent method.  On Unix
287        this default is "/", while on Microsoft Windows it is "\\".  This is required for
288        compatibility with the original behavior of this class. */
289 
290     /**
291      * Creates a new <code>File</code> instance from a parent pathname string
292      * and a child pathname string.
293      *
294      * <p> If <code>parent</code> is <code>null</code> then the new
295      * <code>File</code> instance is created as if by invoking the
296      * single-argument <code>File</code> constructor on the given
297      * <code>child</code> pathname string.
298      *
299      * <p> Otherwise the <code>parent</code> pathname string is taken to denote
300      * a directory, and the <code>child</code> pathname string is taken to
301      * denote either a directory or a file.  If the <code>child</code> pathname
302      * string is absolute then it is converted into a relative pathname in a
303      * system-dependent way.  If <code>parent</code> is the empty string then
304      * the new <code>File</code> instance is created by converting
305      * <code>child</code> into an abstract pathname and resolving the result
306      * against a system-dependent default directory.  Otherwise each pathname
307      * string is converted into an abstract pathname and the child abstract
308      * pathname is resolved against the parent.
309      *
310      * @param   parent  The parent pathname string
311      * @param   child   The child pathname string
312      * @throws  NullPointerException
313      *          If <code>child</code> is <code>null</code>
314      */
315     public File(String parent, String child) {
316         if (child == null) {
317             throw new NullPointerException();
318         }
319         if (parent != null) {
320             if (parent.equals("")) {
321                 this.path = fs.resolve(fs.getDefaultParent(),
322                                        fs.normalize(child));
323             } else {
324                 this.path = fs.resolve(fs.normalize(parent),
325                                        fs.normalize(child));
326             }
327         } else {
328             this.path = fs.normalize(child);
329         }
330         this.prefixLength = fs.prefixLength(this.path);
331     }
332 
333     /**
334      * Creates a new <code>File</code> instance from a parent abstract
335      * pathname and a child pathname string.
336      *
337      * <p> If <code>parent</code> is <code>null</code> then the new
338      * <code>File</code> instance is created as if by invoking the
339      * single-argument <code>File</code> constructor on the given
340      * <code>child</code> pathname string.
341      *
342      * <p> Otherwise the <code>parent</code> abstract pathname is taken to
343      * denote a directory, and the <code>child</code> pathname string is taken
344      * to denote either a directory or a file.  If the <code>child</code>
345      * pathname string is absolute then it is converted into a relative
346      * pathname in a system-dependent way.  If <code>parent</code> is the empty
347      * abstract pathname then the new <code>File</code> instance is created by
348      * converting <code>child</code> into an abstract pathname and resolving
349      * the result against a system-dependent default directory.  Otherwise each
350      * pathname string is converted into an abstract pathname and the child
351      * abstract pathname is resolved against the parent.
352      *
353      * @param   parent  The parent abstract pathname
354      * @param   child   The child pathname string
355      * @throws  NullPointerException
356      *          If <code>child</code> is <code>null</code>
357      */
358     public File(File parent, String child) {
359         if (child == null) {
360             throw new NullPointerException();
361         }
362         if (parent != null) {
363             if (parent.path.equals("")) {
364                 this.path = fs.resolve(fs.getDefaultParent(),
365                                        fs.normalize(child));
366             } else {
367                 this.path = fs.resolve(parent.path,
368                                        fs.normalize(child));
369             }
370         } else {
371             this.path = fs.normalize(child);
372         }
373         this.prefixLength = fs.prefixLength(this.path);
374     }
375 
376     /**
377      * Creates a new <tt>File</tt> instance by converting the given
378      * <tt>file:</tt> URI into an abstract pathname.
379      *
380      * <p> The exact form of a <tt>file:</tt> URI is system-dependent, hence
381      * the transformation performed by this constructor is also
382      * system-dependent.
383      *
384      * <p> For a given abstract pathname <i>f</i> it is guaranteed that
385      *
386      * <blockquote><tt>
387      * new File(</tt><i>&nbsp;f</i><tt>.{@link #toURI() toURI}()).equals(</tt><i>&nbsp;f</i><tt>.{@link #getAbsoluteFile() getAbsoluteFile}())
388      * </tt></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 <tt>file:</tt> 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      *         <tt>"file"</tt>, a non-empty path component, and undefined
400      *         authority, query, and fragment components
401      *
402      * @throws  NullPointerException
403      *          If <tt>uri</tt> is <tt>null</tt>
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.getAuthority() != null)
423             throw new IllegalArgumentException("URI has an authority component");
424         if (uri.getFragment() != null)
425             throw new IllegalArgumentException("URI has a fragment component");
426         if (uri.getQuery() != 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 <code>{@link #getPath}</code>
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 <tt>"."</tt> and <tt>".."</tt> 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 <code>{@link
608      *          java.lang.SecurityManager#checkRead}</code> method denies
609      *          read access to the file
610      *
611      * @since   JDK1.1
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 <code>{@link
636      *          java.lang.SecurityManager#checkRead}</code> 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 <tt>file:</tt> 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><tt>
699      * new {@link #File(java.net.URI) File}(</tt><i>&nbsp;f</i><tt>.toURI()).equals(</tt><i>&nbsp;f</i><tt>.{@link #getAbsoluteFile() getAbsoluteFile}())
700      * </tt></blockquote>
701      *
702      * so long as the original abstract pathname, the URI, and the new abstract
703      * pathname are all created in (possibly different invocations of) the same
704      * Java virtual machine.  Due to the system-dependent nature of abstract
705      * pathnames, however, this relationship typically does not hold when a
706      * <tt>file:</tt> URI that is created in a virtual machine on one operating
707      * system is converted into an abstract pathname in a virtual machine on a
708      * different operating system.
709      *
710      * <p> Note that when this abstract pathname represents a UNC pathname then
711      * all components of the UNC (including the server name component) are encoded
712      * in the {@code URI} path. The authority component is undefined, meaning
713      * that it is represented as {@code null}. The {@link Path} class defines the
714      * {@link Path#toUri toUri} method to encode the server name in the authority
715      * component of the resulting {@code URI}. The {@link #toPath toPath} method
716      * may be used to obtain a {@code Path} representing this abstract pathname.
717      *
718      * @return  An absolute, hierarchical URI with a scheme equal to
719      *          <tt>"file"</tt>, a path representing this abstract pathname,
720      *          and undefined authority, query, and fragment components
721      * @throws SecurityException If a required system property value cannot
722      * be accessed.
723      *
724      * @see #File(java.net.URI)
725      * @see java.net.URI
726      * @see java.net.URI#toURL()
727      * @since 1.4
728      */
729     public URI toURI() {
730         try {
731             File f = getAbsoluteFile();
732             String sp = slashify(f.getPath(), f.isDirectory());
733             if (sp.startsWith("//"))
734                 sp = "//" + sp;
735             return new URI("file", null, sp, null);
736         } catch (URISyntaxException x) {
737             throw new Error(x);         // Can't happen
738         }
739     }
740 
741 
742     /* -- Attribute accessors -- */
743 
744     /**
745      * Tests whether the application can read the file denoted by this
746      * abstract pathname. On some platforms it may be possible to start the
747      * Java virtual machine with special privileges that allow it to read
748      * files that are marked as unreadable. Consequently this method may return
749      * {@code true} even though the file does not have read permissions.
750      *
751      * @return  <code>true</code> if and only if the file specified by this
752      *          abstract pathname exists <em>and</em> can be read by the
753      *          application; <code>false</code> otherwise
754      *
755      * @throws  SecurityException
756      *          If a security manager exists and its <code>{@link
757      *          java.lang.SecurityManager#checkRead(java.lang.String)}</code>
758      *          method denies read access to the file
759      */
760     public boolean canRead() {
761         SecurityManager security = System.getSecurityManager();
762         if (security != null) {
763             security.checkRead(path);
764         }
765         if (isInvalid()) {
766             return false;
767         }
768         return fs.checkAccess(this, FileSystem.ACCESS_READ);
769     }
770 
771     /**
772      * Tests whether the application can modify the file denoted by this
773      * abstract pathname. On some platforms it may be possible to start the
774      * Java virtual machine with special privileges that allow it to modify
775      * files that are marked read-only. Consequently this method may return
776      * {@code true} even though the file is marked read-only.
777      *
778      * @return  <code>true</code> if and only if the file system actually
779      *          contains a file denoted by this abstract pathname <em>and</em>
780      *          the application is allowed to write to the file;
781      *          <code>false</code> otherwise.
782      *
783      * @throws  SecurityException
784      *          If a security manager exists and its <code>{@link
785      *          java.lang.SecurityManager#checkWrite(java.lang.String)}</code>
786      *          method denies write access to the file
787      */
788     public boolean canWrite() {
789         SecurityManager security = System.getSecurityManager();
790         if (security != null) {
791             security.checkWrite(path);
792         }
793         if (isInvalid()) {
794             return false;
795         }
796         return fs.checkAccess(this, FileSystem.ACCESS_WRITE);
797     }
798 
799     /**
800      * Tests whether the file or directory denoted by this abstract pathname
801      * exists.
802      *
803      * @return  <code>true</code> if and only if the file or directory denoted
804      *          by this abstract pathname exists; <code>false</code> otherwise
805      *
806      * @throws  SecurityException
807      *          If a security manager exists and its <code>{@link
808      *          java.lang.SecurityManager#checkRead(java.lang.String)}</code>
809      *          method denies read access to the file or directory
810      */
811     public boolean exists() {
812         SecurityManager security = System.getSecurityManager();
813         if (security != null) {
814             security.checkRead(path);
815         }
816         if (isInvalid()) {
817             return false;
818         }
819         return ((fs.getBooleanAttributes(this) & FileSystem.BA_EXISTS) != 0);
820     }
821 
822     /**
823      * Tests whether the file denoted by this abstract pathname is a
824      * directory.
825      *
826      * <p> Where it is required to distinguish an I/O exception from the case
827      * that the file is not a directory, or where several attributes of the
828      * same file are required at the same time, then the {@link
829      * java.nio.file.Files#readAttributes(Path,Class,LinkOption[])
830      * Files.readAttributes} method may be used.
831      *
832      * @return <code>true</code> if and only if the file denoted by this
833      *          abstract pathname exists <em>and</em> is a directory;
834      *          <code>false</code> otherwise
835      *
836      * @throws  SecurityException
837      *          If a security manager exists and its <code>{@link
838      *          java.lang.SecurityManager#checkRead(java.lang.String)}</code>
839      *          method denies read access to the file
840      */
841     public boolean isDirectory() {
842         SecurityManager security = System.getSecurityManager();
843         if (security != null) {
844             security.checkRead(path);
845         }
846         if (isInvalid()) {
847             return false;
848         }
849         return ((fs.getBooleanAttributes(this) & FileSystem.BA_DIRECTORY)
850                 != 0);
851     }
852 
853     /**
854      * Tests whether the file denoted by this abstract pathname is a normal
855      * file.  A file is <em>normal</em> if it is not a directory and, in
856      * addition, satisfies other system-dependent criteria.  Any non-directory
857      * file created by a Java application is guaranteed to be a normal file.
858      *
859      * <p> Where it is required to distinguish an I/O exception from the case
860      * that the file is not a normal file, or where several attributes of the
861      * same file are required at the same time, then the {@link
862      * java.nio.file.Files#readAttributes(Path,Class,LinkOption[])
863      * Files.readAttributes} method may be used.
864      *
865      * @return  <code>true</code> if and only if the file denoted by this
866      *          abstract pathname exists <em>and</em> is a normal file;
867      *          <code>false</code> otherwise
868      *
869      * @throws  SecurityException
870      *          If a security manager exists and its <code>{@link
871      *          java.lang.SecurityManager#checkRead(java.lang.String)}</code>
872      *          method denies read access to the file
873      */
874     public boolean isFile() {
875         SecurityManager security = System.getSecurityManager();
876         if (security != null) {
877             security.checkRead(path);
878         }
879         if (isInvalid()) {
880             return false;
881         }
882         return ((fs.getBooleanAttributes(this) & FileSystem.BA_REGULAR) != 0);
883     }
884 
885     /**
886      * Tests whether the file named by this abstract pathname is a hidden
887      * file.  The exact definition of <em>hidden</em> is system-dependent.  On
888      * UNIX systems, a file is considered to be hidden if its name begins with
889      * a period character (<code>'.'</code>).  On Microsoft Windows systems, a file is
890      * considered to be hidden if it has been marked as such in the filesystem.
891      *
892      * @return  <code>true</code> if and only if the file denoted by this
893      *          abstract pathname is hidden according to the conventions of the
894      *          underlying platform
895      *
896      * @throws  SecurityException
897      *          If a security manager exists and its <code>{@link
898      *          java.lang.SecurityManager#checkRead(java.lang.String)}</code>
899      *          method denies read access to the file
900      *
901      * @since 1.2
902      */
903     public boolean isHidden() {
904         SecurityManager security = System.getSecurityManager();
905         if (security != null) {
906             security.checkRead(path);
907         }
908         if (isInvalid()) {
909             return false;
910         }
911         return ((fs.getBooleanAttributes(this) & FileSystem.BA_HIDDEN) != 0);
912     }
913 
914     /**
915      * Returns the time that the file denoted by this abstract pathname was
916      * last modified.
917      *
918      * <p> Where it is required to distinguish an I/O exception from the case
919      * where {@code 0L} is returned, or where several attributes of the
920      * same file are required at the same time, or where the time of last
921      * access or the creation time are required, then the {@link
922      * java.nio.file.Files#readAttributes(Path,Class,LinkOption[])
923      * Files.readAttributes} method may be used.
924      *
925      * @return  A <code>long</code> value representing the time the file was
926      *          last modified, measured in milliseconds since the epoch
927      *          (00:00:00 GMT, January 1, 1970), or <code>0L</code> if the
928      *          file does not exist or if an I/O error occurs
929      *
930      * @throws  SecurityException
931      *          If a security manager exists and its <code>{@link
932      *          java.lang.SecurityManager#checkRead(java.lang.String)}</code>
933      *          method denies read access to the file
934      */
935     public long lastModified() {
936         SecurityManager security = System.getSecurityManager();
937         if (security != null) {
938             security.checkRead(path);
939         }
940         if (isInvalid()) {
941             return 0L;
942         }
943         return fs.getLastModifiedTime(this);
944     }
945 
946     /**
947      * Returns the length of the file denoted by this abstract pathname.
948      * The return value is unspecified if this pathname denotes a directory.
949      *
950      * <p> Where it is required to distinguish an I/O exception from the case
951      * that {@code 0L} is returned, or where several attributes of the same file
952      * are required at the same time, then the {@link
953      * java.nio.file.Files#readAttributes(Path,Class,LinkOption[])
954      * Files.readAttributes} method may be used.
955      *
956      * @return  The length, in bytes, of the file denoted by this abstract
957      *          pathname, or <code>0L</code> if the file does not exist.  Some
958      *          operating systems may return <code>0L</code> for pathnames
959      *          denoting system-dependent entities such as devices or pipes.
960      *
961      * @throws  SecurityException
962      *          If a security manager exists and its <code>{@link
963      *          java.lang.SecurityManager#checkRead(java.lang.String)}</code>
964      *          method denies read access to the file
965      */
966     public long length() {
967         SecurityManager security = System.getSecurityManager();
968         if (security != null) {
969             security.checkRead(path);
970         }
971         if (isInvalid()) {
972             return 0L;
973         }
974         return fs.getLength(this);
975     }
976 
977 
978     /* -- File operations -- */
979 
980     /**
981      * Atomically creates a new, empty file named by this abstract pathname if
982      * and only if a file with this name does not yet exist.  The check for the
983      * existence of the file and the creation of the file if it does not exist
984      * are a single operation that is atomic with respect to all other
985      * filesystem activities that might affect the file.
986      * <P>
987      * Note: this method should <i>not</i> be used for file-locking, as
988      * the resulting protocol cannot be made to work reliably. The
989      * {@link java.nio.channels.FileLock FileLock}
990      * facility should be used instead.
991      *
992      * @return  <code>true</code> if the named file does not exist and was
993      *          successfully created; <code>false</code> if the named file
994      *          already exists
995      *
996      * @throws  IOException
997      *          If an I/O error occurred
998      *
999      * @throws  SecurityException
1000      *          If a security manager exists and its <code>{@link
1001      *          java.lang.SecurityManager#checkWrite(java.lang.String)}</code>
1002      *          method denies write access to the file
1003      *
1004      * @since 1.2
1005      */
1006     public boolean createNewFile() throws IOException {
1007         SecurityManager security = System.getSecurityManager();
1008         if (security != null) security.checkWrite(path);
1009         if (isInvalid()) {
1010             throw new IOException("Invalid file path");
1011         }
1012         return fs.createFileExclusively(path);
1013     }
1014 
1015     /**
1016      * Deletes the file or directory denoted by this abstract pathname.  If
1017      * this pathname denotes a directory, then the directory must be empty in
1018      * order to be deleted.
1019      *
1020      * <p> Note that the {@link java.nio.file.Files} class defines the {@link
1021      * java.nio.file.Files#delete(Path) delete} method to throw an {@link IOException}
1022      * when a file cannot be deleted. This is useful for error reporting and to
1023      * diagnose why a file cannot be deleted.
1024      *
1025      * @return  <code>true</code> if and only if the file or directory is
1026      *          successfully deleted; <code>false</code> otherwise
1027      *
1028      * @throws  SecurityException
1029      *          If a security manager exists and its <code>{@link
1030      *          java.lang.SecurityManager#checkDelete}</code> method denies
1031      *          delete access to the file
1032      */
1033     public boolean delete() {
1034         SecurityManager security = System.getSecurityManager();
1035         if (security != null) {
1036             security.checkDelete(path);
1037         }
1038         if (isInvalid()) {
1039             return false;
1040         }
1041         return fs.delete(this);
1042     }
1043 
1044     /**
1045      * Requests that the file or directory denoted by this abstract
1046      * pathname be deleted when the virtual machine terminates.
1047      * Files (or directories) are deleted in the reverse order that
1048      * they are registered. Invoking this method to delete a file or
1049      * directory that is already registered for deletion has no effect.
1050      * Deletion will be attempted only for normal termination of the
1051      * virtual machine, as defined by the Java Language Specification.
1052      *
1053      * <p> Once deletion has been requested, it is not possible to cancel the
1054      * request.  This method should therefore be used with care.
1055      *
1056      * <P>
1057      * Note: this method should <i>not</i> be used for file-locking, as
1058      * the resulting protocol cannot be made to work reliably. The
1059      * {@link java.nio.channels.FileLock FileLock}
1060      * facility should be used instead.
1061      *
1062      * @throws  SecurityException
1063      *          If a security manager exists and its <code>{@link
1064      *          java.lang.SecurityManager#checkDelete}</code> method denies
1065      *          delete access to the file
1066      *
1067      * @see #delete
1068      *
1069      * @since 1.2
1070      */
1071     public void deleteOnExit() {
1072         SecurityManager security = System.getSecurityManager();
1073         if (security != null) {
1074             security.checkDelete(path);
1075         }
1076         if (isInvalid()) {
1077             return;
1078         }
1079         DeleteOnExitHook.add(path);
1080     }
1081 
1082     /**
1083      * Returns an array of strings naming the files and directories in the
1084      * directory denoted by this abstract pathname.
1085      *
1086      * <p> If this abstract pathname does not denote a directory, then this
1087      * method returns {@code null}.  Otherwise an array of strings is
1088      * returned, one for each file or directory in the directory.  Names
1089      * denoting the directory itself and the directory's parent directory are
1090      * not included in the result.  Each string is a file name rather than a
1091      * complete path.
1092      *
1093      * <p> There is no guarantee that the name strings in the resulting array
1094      * will appear in any specific order; they are not, in particular,
1095      * guaranteed to appear in alphabetical order.
1096      *
1097      * <p> Note that the {@link java.nio.file.Files} class defines the {@link
1098      * java.nio.file.Files#newDirectoryStream(Path) newDirectoryStream} method to
1099      * open a directory and iterate over the names of the files in the directory.
1100      * This may use less resources when working with very large directories, and
1101      * may be more responsive when working with remote directories.
1102      *
1103      * @return  An array of strings naming the files and directories in the
1104      *          directory denoted by this abstract pathname.  The array will be
1105      *          empty if the directory is empty.  Returns {@code null} if
1106      *          this abstract pathname does not denote a directory, or if an
1107      *          I/O error occurs.
1108      *
1109      * @throws  SecurityException
1110      *          If a security manager exists and its {@link
1111      *          SecurityManager#checkRead(String)} method denies read access to
1112      *          the directory
1113      */
1114     public String[] list() {
1115         SecurityManager security = System.getSecurityManager();
1116         if (security != null) {
1117             security.checkRead(path);
1118         }
1119         if (isInvalid()) {
1120             return null;
1121         }
1122         return fs.list(this);
1123     }
1124 
1125     /**
1126      * Returns an array of strings naming the files and directories in the
1127      * directory denoted by this abstract pathname that satisfy the specified
1128      * filter.  The behavior of this method is the same as that of the
1129      * {@link #list()} method, except that the strings in the returned array
1130      * must satisfy the filter.  If the given {@code filter} is {@code null}
1131      * then all names are accepted.  Otherwise, a name satisfies the filter if
1132      * and only if the value {@code true} results when the {@link
1133      * FilenameFilter#accept FilenameFilter.accept(File,&nbsp;String)} method
1134      * of the filter is invoked on this abstract pathname and the name of a
1135      * file or directory in the directory that it denotes.
1136      *
1137      * @param  filter
1138      *         A filename filter
1139      *
1140      * @return  An array of strings naming the files and directories in the
1141      *          directory denoted by this abstract pathname that were accepted
1142      *          by the given {@code filter}.  The array will be empty if the
1143      *          directory is empty or if no names were accepted by the filter.
1144      *          Returns {@code null} if this abstract pathname does not denote
1145      *          a directory, or if an I/O error occurs.
1146      *
1147      * @throws  SecurityException
1148      *          If a security manager exists and its {@link
1149      *          SecurityManager#checkRead(String)} method denies read access to
1150      *          the directory
1151      *
1152      * @see java.nio.file.Files#newDirectoryStream(Path,String)
1153      */
1154     public String[] list(FilenameFilter filter) {
1155         String names[] = list();
1156         if ((names == null) || (filter == null)) {
1157             return names;
1158         }
1159         List<String> v = new ArrayList<>();
1160         for (int i = 0 ; i < names.length ; i++) {
1161             if (filter.accept(this, names[i])) {
1162                 v.add(names[i]);
1163             }
1164         }
1165         return v.toArray(new String[v.size()]);
1166     }
1167 
1168     /**
1169      * Returns an array of abstract pathnames denoting the files in the
1170      * directory denoted by this abstract pathname.
1171      *
1172      * <p> If this abstract pathname does not denote a directory, then this
1173      * method returns {@code null}.  Otherwise an array of {@code File} objects
1174      * is returned, one for each file or directory in the directory.  Pathnames
1175      * denoting the directory itself and the directory's parent directory are
1176      * not included in the result.  Each resulting abstract pathname is
1177      * constructed from this abstract pathname using the {@link #File(File,
1178      * String) File(File,&nbsp;String)} constructor.  Therefore if this
1179      * pathname is absolute then each resulting pathname is absolute; if this
1180      * pathname is relative then each resulting pathname will be relative to
1181      * the same directory.
1182      *
1183      * <p> There is no guarantee that the name strings in the resulting array
1184      * will appear in any specific order; they are not, in particular,
1185      * guaranteed to appear in alphabetical order.
1186      *
1187      * <p> Note that the {@link java.nio.file.Files} class defines the {@link
1188      * java.nio.file.Files#newDirectoryStream(Path) newDirectoryStream} method
1189      * to open a directory and iterate over the names of the files in the
1190      * directory. This may use less resources when working with very large
1191      * directories.
1192      *
1193      * @return  An array of abstract pathnames denoting the files and
1194      *          directories in the directory denoted by this abstract pathname.
1195      *          The array will be empty if the directory is empty.  Returns
1196      *          {@code null} if this abstract pathname does not denote a
1197      *          directory, or if an I/O error occurs.
1198      *
1199      * @throws  SecurityException
1200      *          If a security manager exists and its {@link
1201      *          SecurityManager#checkRead(String)} method denies read access to
1202      *          the directory
1203      *
1204      * @since  1.2
1205      */
1206     public File[] listFiles() {
1207         String[] ss = list();
1208         if (ss == null) return null;
1209         int n = ss.length;
1210         File[] fs = new File[n];
1211         for (int i = 0; i < n; i++) {
1212             fs[i] = new File(ss[i], this);
1213         }
1214         return fs;
1215     }
1216 
1217     /**
1218      * Returns an array of abstract pathnames denoting the files and
1219      * directories in the directory denoted by this abstract pathname that
1220      * satisfy the specified filter.  The behavior of this method is the same
1221      * as that of the {@link #listFiles()} method, except that the pathnames in
1222      * the returned array must satisfy the filter.  If the given {@code filter}
1223      * is {@code null} then all pathnames are accepted.  Otherwise, a pathname
1224      * satisfies the filter if and only if the value {@code true} results when
1225      * the {@link FilenameFilter#accept
1226      * FilenameFilter.accept(File,&nbsp;String)} method of the filter is
1227      * invoked on this abstract pathname and the name of a file or directory in
1228      * the directory that it denotes.
1229      *
1230      * @param  filter
1231      *         A filename filter
1232      *
1233      * @return  An array of abstract pathnames denoting the files and
1234      *          directories in the directory denoted by this abstract pathname.
1235      *          The array will be empty if the directory is empty.  Returns
1236      *          {@code null} if this abstract pathname does not denote a
1237      *          directory, or if an I/O error occurs.
1238      *
1239      * @throws  SecurityException
1240      *          If a security manager exists and its {@link
1241      *          SecurityManager#checkRead(String)} method denies read access to
1242      *          the directory
1243      *
1244      * @since  1.2
1245      * @see java.nio.file.Files#newDirectoryStream(Path,String)
1246      */
1247     public File[] listFiles(FilenameFilter filter) {
1248         String ss[] = list();
1249         if (ss == null) return null;
1250         ArrayList<File> files = new ArrayList<>();
1251         for (String s : ss)
1252             if ((filter == null) || filter.accept(this, s))
1253                 files.add(new File(s, this));
1254         return files.toArray(new File[files.size()]);
1255     }
1256 
1257     /**
1258      * Returns an array of abstract pathnames denoting the files and
1259      * directories in the directory denoted by this abstract pathname that
1260      * satisfy the specified filter.  The behavior of this method is the same
1261      * as that of the {@link #listFiles()} method, except that the pathnames in
1262      * the returned array must satisfy the filter.  If the given {@code filter}
1263      * is {@code null} then all pathnames are accepted.  Otherwise, a pathname
1264      * satisfies the filter if and only if the value {@code true} results when
1265      * the {@link FileFilter#accept FileFilter.accept(File)} method of the
1266      * filter is invoked on the pathname.
1267      *
1268      * @param  filter
1269      *         A file filter
1270      *
1271      * @return  An array of abstract pathnames denoting the files and
1272      *          directories in the directory denoted by this abstract pathname.
1273      *          The array will be empty if the directory is empty.  Returns
1274      *          {@code null} if this abstract pathname does not denote a
1275      *          directory, or if an I/O error occurs.
1276      *
1277      * @throws  SecurityException
1278      *          If a security manager exists and its {@link
1279      *          SecurityManager#checkRead(String)} method denies read access to
1280      *          the directory
1281      *
1282      * @since  1.2
1283      * @see java.nio.file.Files#newDirectoryStream(Path,java.nio.file.DirectoryStream.Filter)
1284      */
1285     public File[] listFiles(FileFilter filter) {
1286         String ss[] = list();
1287         if (ss == null) return null;
1288         ArrayList<File> files = new ArrayList<>();
1289         for (String s : ss) {
1290             File f = new File(s, this);
1291             if ((filter == null) || filter.accept(f))
1292                 files.add(f);
1293         }
1294         return files.toArray(new File[files.size()]);
1295     }
1296 
1297     /**
1298      * Creates the directory named by this abstract pathname.
1299      *
1300      * @return  <code>true</code> if and only if the directory was
1301      *          created; <code>false</code> otherwise
1302      *
1303      * @throws  SecurityException
1304      *          If a security manager exists and its <code>{@link
1305      *          java.lang.SecurityManager#checkWrite(java.lang.String)}</code>
1306      *          method does not permit the named directory to be created
1307      */
1308     public boolean mkdir() {
1309         SecurityManager security = System.getSecurityManager();
1310         if (security != null) {
1311             security.checkWrite(path);
1312         }
1313         if (isInvalid()) {
1314             return false;
1315         }
1316         return fs.createDirectory(this);
1317     }
1318 
1319     /**
1320      * Creates the directory named by this abstract pathname, including any
1321      * necessary but nonexistent parent directories.  Note that if this
1322      * operation fails it may have succeeded in creating some of the necessary
1323      * parent directories.
1324      *
1325      * @return  <code>true</code> if and only if the directory was created,
1326      *          along with all necessary parent directories; <code>false</code>
1327      *          otherwise
1328      *
1329      * @throws  SecurityException
1330      *          If a security manager exists and its <code>{@link
1331      *          java.lang.SecurityManager#checkRead(java.lang.String)}</code>
1332      *          method does not permit verification of the existence of the
1333      *          named directory and all necessary parent directories; or if
1334      *          the <code>{@link
1335      *          java.lang.SecurityManager#checkWrite(java.lang.String)}</code>
1336      *          method does not permit the named directory and all necessary
1337      *          parent directories to be created
1338      */
1339     public boolean mkdirs() {
1340         if (exists()) {
1341             return false;
1342         }
1343         if (mkdir()) {
1344             return true;
1345         }
1346         File canonFile = null;
1347         try {
1348             canonFile = getCanonicalFile();
1349         } catch (IOException e) {
1350             return false;
1351         }
1352 
1353         File parent = canonFile.getParentFile();
1354         return (parent != null && (parent.mkdirs() || parent.exists()) &&
1355                 canonFile.mkdir());
1356     }
1357 
1358     /**
1359      * Renames the file denoted by this abstract pathname.
1360      *
1361      * <p> Many aspects of the behavior of this method are inherently
1362      * platform-dependent: The rename operation might not be able to move a
1363      * file from one filesystem to another, it might not be atomic, and it
1364      * might not succeed if a file with the destination abstract pathname
1365      * already exists.  The return value should always be checked to make sure
1366      * that the rename operation was successful.
1367      *
1368      * <p> Note that the {@link java.nio.file.Files} class defines the {@link
1369      * java.nio.file.Files#move move} method to move or rename a file in a
1370      * platform independent manner.
1371      *
1372      * @param  dest  The new abstract pathname for the named file
1373      *
1374      * @return  <code>true</code> if and only if the renaming succeeded;
1375      *          <code>false</code> otherwise
1376      *
1377      * @throws  SecurityException
1378      *          If a security manager exists and its <code>{@link
1379      *          java.lang.SecurityManager#checkWrite(java.lang.String)}</code>
1380      *          method denies write access to either the old or new pathnames
1381      *
1382      * @throws  NullPointerException
1383      *          If parameter <code>dest</code> is <code>null</code>
1384      */
1385     public boolean renameTo(File dest) {
1386         SecurityManager security = System.getSecurityManager();
1387         if (security != null) {
1388             security.checkWrite(path);
1389             security.checkWrite(dest.path);
1390         }
1391         if (dest == null) {
1392             throw new NullPointerException();
1393         }
1394         if (this.isInvalid() || dest.isInvalid()) {
1395             return false;
1396         }
1397         return fs.rename(this, dest);
1398     }
1399 
1400     /**
1401      * Sets the last-modified time of the file or directory named by this
1402      * abstract pathname.
1403      *
1404      * <p> All platforms support file-modification times to the nearest second,
1405      * but some provide more precision.  The argument will be truncated to fit
1406      * the supported precision.  If the operation succeeds and no intervening
1407      * operations on the file take place, then the next invocation of the
1408      * <code>{@link #lastModified}</code> method will return the (possibly
1409      * truncated) <code>time</code> argument that was passed to this method.
1410      *
1411      * @param  time  The new last-modified time, measured in milliseconds since
1412      *               the epoch (00:00:00 GMT, January 1, 1970)
1413      *
1414      * @return <code>true</code> if and only if the operation succeeded;
1415      *          <code>false</code> otherwise
1416      *
1417      * @throws  IllegalArgumentException  If the argument is negative
1418      *
1419      * @throws  SecurityException
1420      *          If a security manager exists and its <code>{@link
1421      *          java.lang.SecurityManager#checkWrite(java.lang.String)}</code>
1422      *          method denies write access to the named file
1423      *
1424      * @since 1.2
1425      */
1426     public boolean setLastModified(long time) {
1427         if (time < 0) throw new IllegalArgumentException("Negative time");
1428         SecurityManager security = System.getSecurityManager();
1429         if (security != null) {
1430             security.checkWrite(path);
1431         }
1432         if (isInvalid()) {
1433             return false;
1434         }
1435         return fs.setLastModifiedTime(this, time);
1436     }
1437 
1438     /**
1439      * Marks the file or directory named by this abstract pathname so that
1440      * only read operations are allowed. After invoking this method the file
1441      * or directory will not change until it is either deleted or marked
1442      * to allow write access. On some platforms it may be possible to start the
1443      * Java virtual machine with special privileges that allow it to modify
1444      * files that are marked read-only. Whether or not a read-only file or
1445      * directory may be deleted depends upon the underlying system.
1446      *
1447      * @return <code>true</code> if and only if the operation succeeded;
1448      *          <code>false</code> otherwise
1449      *
1450      * @throws  SecurityException
1451      *          If a security manager exists and its <code>{@link
1452      *          java.lang.SecurityManager#checkWrite(java.lang.String)}</code>
1453      *          method denies write access to the named file
1454      *
1455      * @since 1.2
1456      */
1457     public boolean setReadOnly() {
1458         SecurityManager security = System.getSecurityManager();
1459         if (security != null) {
1460             security.checkWrite(path);
1461         }
1462         if (isInvalid()) {
1463             return false;
1464         }
1465         return fs.setReadOnly(this);
1466     }
1467 
1468     /**
1469      * Sets the owner's or everybody's write permission for this abstract
1470      * pathname. On some platforms it may be possible to start the Java virtual
1471      * machine with special privileges that allow it to modify files that
1472      * disallow write operations.
1473      *
1474      * <p> The {@link java.nio.file.Files} class defines methods that operate on
1475      * file attributes including file permissions. This may be used when finer
1476      * manipulation of file permissions is required.
1477      *
1478      * @param   writable
1479      *          If <code>true</code>, sets the access permission to allow write
1480      *          operations; if <code>false</code> to disallow write operations
1481      *
1482      * @param   ownerOnly
1483      *          If <code>true</code>, the write permission applies only to the
1484      *          owner's write permission; otherwise, it applies to everybody.  If
1485      *          the underlying file system can not distinguish the owner's write
1486      *          permission from that of others, then the permission will apply to
1487      *          everybody, regardless of this value.
1488      *
1489      * @return  <code>true</code> if and only if the operation succeeded. The
1490      *          operation will fail if the user does not have permission to change
1491      *          the access permissions of this abstract pathname.
1492      *
1493      * @throws  SecurityException
1494      *          If a security manager exists and its <code>{@link
1495      *          java.lang.SecurityManager#checkWrite(java.lang.String)}</code>
1496      *          method denies write access to the named file
1497      *
1498      * @since 1.6
1499      */
1500     public boolean setWritable(boolean writable, boolean ownerOnly) {
1501         SecurityManager security = System.getSecurityManager();
1502         if (security != null) {
1503             security.checkWrite(path);
1504         }
1505         if (isInvalid()) {
1506             return false;
1507         }
1508         return fs.setPermission(this, FileSystem.ACCESS_WRITE, writable, ownerOnly);
1509     }
1510 
1511     /**
1512      * A convenience method to set the owner's write permission for this abstract
1513      * pathname. On some platforms it may be possible to start the Java virtual
1514      * machine with special privileges that allow it to modify files that
1515      * disallow write operations.
1516      *
1517      * <p> An invocation of this method of the form <tt>file.setWritable(arg)</tt>
1518      * behaves in exactly the same way as the invocation
1519      *
1520      * <pre>
1521      *     file.setWritable(arg, true) </pre>
1522      *
1523      * @param   writable
1524      *          If <code>true</code>, sets the access permission to allow write
1525      *          operations; if <code>false</code> to disallow write operations
1526      *
1527      * @return  <code>true</code> if and only if the operation succeeded.  The
1528      *          operation will fail if the user does not have permission to
1529      *          change the access permissions of this abstract pathname.
1530      *
1531      * @throws  SecurityException
1532      *          If a security manager exists and its <code>{@link
1533      *          java.lang.SecurityManager#checkWrite(java.lang.String)}</code>
1534      *          method denies write access to the file
1535      *
1536      * @since 1.6
1537      */
1538     public boolean setWritable(boolean writable) {
1539         return setWritable(writable, true);
1540     }
1541 
1542     /**
1543      * Sets the owner's or everybody's read permission for this abstract
1544      * pathname. On some platforms it may be possible to start the Java virtual
1545      * machine with special privileges that allow it to read files that are
1546      * marked as unreadable.
1547      *
1548      * <p> The {@link java.nio.file.Files} class defines methods that operate on
1549      * file attributes including file permissions. This may be used when finer
1550      * manipulation of file permissions is required.
1551      *
1552      * @param   readable
1553      *          If <code>true</code>, sets the access permission to allow read
1554      *          operations; if <code>false</code> to disallow read operations
1555      *
1556      * @param   ownerOnly
1557      *          If <code>true</code>, the read permission applies only to the
1558      *          owner's read permission; otherwise, it applies to everybody.  If
1559      *          the underlying file system can not distinguish the owner's read
1560      *          permission from that of others, then the permission will apply to
1561      *          everybody, regardless of this value.
1562      *
1563      * @return  <code>true</code> if and only if the operation succeeded.  The
1564      *          operation will fail if the user does not have permission to
1565      *          change the access permissions of this abstract pathname.  If
1566      *          <code>readable</code> is <code>false</code> and the underlying
1567      *          file system does not implement a read permission, then the
1568      *          operation will fail.
1569      *
1570      * @throws  SecurityException
1571      *          If a security manager exists and its <code>{@link
1572      *          java.lang.SecurityManager#checkWrite(java.lang.String)}</code>
1573      *          method denies write access to the file
1574      *
1575      * @since 1.6
1576      */
1577     public boolean setReadable(boolean readable, boolean ownerOnly) {
1578         SecurityManager security = System.getSecurityManager();
1579         if (security != null) {
1580             security.checkWrite(path);
1581         }
1582         if (isInvalid()) {
1583             return false;
1584         }
1585         return fs.setPermission(this, FileSystem.ACCESS_READ, readable, ownerOnly);
1586     }
1587 
1588     /**
1589      * A convenience method to set the owner's read permission for this abstract
1590      * pathname. On some platforms it may be possible to start the Java virtual
1591      * machine with special privileges that allow it to read files that that are
1592      * marked as unreadable.
1593      *
1594      * <p>An invocation of this method of the form <tt>file.setReadable(arg)</tt>
1595      * behaves in exactly the same way as the invocation
1596      *
1597      * <pre>
1598      *     file.setReadable(arg, true) </pre>
1599      *
1600      * @param  readable
1601      *          If <code>true</code>, sets the access permission to allow read
1602      *          operations; if <code>false</code> to disallow read operations
1603      *
1604      * @return  <code>true</code> if and only if the operation succeeded.  The
1605      *          operation will fail if the user does not have permission to
1606      *          change the access permissions of this abstract pathname.  If
1607      *          <code>readable</code> is <code>false</code> and the underlying
1608      *          file system does not implement a read permission, then the
1609      *          operation will fail.
1610      *
1611      * @throws  SecurityException
1612      *          If a security manager exists and its <code>{@link
1613      *          java.lang.SecurityManager#checkWrite(java.lang.String)}</code>
1614      *          method denies write access to the file
1615      *
1616      * @since 1.6
1617      */
1618     public boolean setReadable(boolean readable) {
1619         return setReadable(readable, true);
1620     }
1621 
1622     /**
1623      * Sets the owner's or everybody's execute permission for this abstract
1624      * pathname. On some platforms it may be possible to start the Java virtual
1625      * machine with special privileges that allow it to execute files that are
1626      * not marked executable.
1627      *
1628      * <p> The {@link java.nio.file.Files} class defines methods that operate on
1629      * file attributes including file permissions. This may be used when finer
1630      * manipulation of file permissions is required.
1631      *
1632      * @param   executable
1633      *          If <code>true</code>, sets the access permission to allow execute
1634      *          operations; if <code>false</code> to disallow execute operations
1635      *
1636      * @param   ownerOnly
1637      *          If <code>true</code>, the execute permission applies only to the
1638      *          owner's execute permission; otherwise, it applies to everybody.
1639      *          If the underlying file system can not distinguish the owner's
1640      *          execute permission from that of others, then the permission will
1641      *          apply to everybody, regardless of this value.
1642      *
1643      * @return  <code>true</code> if and only if the operation succeeded.  The
1644      *          operation will fail if the user does not have permission to
1645      *          change the access permissions of this abstract pathname.  If
1646      *          <code>executable</code> is <code>false</code> and the underlying
1647      *          file system does not implement an execute permission, then the
1648      *          operation will fail.
1649      *
1650      * @throws  SecurityException
1651      *          If a security manager exists and its <code>{@link
1652      *          java.lang.SecurityManager#checkWrite(java.lang.String)}</code>
1653      *          method denies write access to the file
1654      *
1655      * @since 1.6
1656      */
1657     public boolean setExecutable(boolean executable, boolean ownerOnly) {
1658         SecurityManager security = System.getSecurityManager();
1659         if (security != null) {
1660             security.checkWrite(path);
1661         }
1662         if (isInvalid()) {
1663             return false;
1664         }
1665         return fs.setPermission(this, FileSystem.ACCESS_EXECUTE, executable, ownerOnly);
1666     }
1667 
1668     /**
1669      * A convenience method to set the owner's execute permission for this
1670      * abstract pathname. On some platforms it may be possible to start the Java
1671      * virtual machine with special privileges that allow it to execute files
1672      * that are not marked executable.
1673      *
1674      * <p>An invocation of this method of the form <tt>file.setExcutable(arg)</tt>
1675      * behaves in exactly the same way as the invocation
1676      *
1677      * <pre>
1678      *     file.setExecutable(arg, true) </pre>
1679      *
1680      * @param   executable
1681      *          If <code>true</code>, sets the access permission to allow execute
1682      *          operations; if <code>false</code> to disallow execute operations
1683      *
1684      * @return   <code>true</code> if and only if the operation succeeded.  The
1685      *           operation will fail if the user does not have permission to
1686      *           change the access permissions of this abstract pathname.  If
1687      *           <code>executable</code> is <code>false</code> and the underlying
1688      *           file system does not implement an execute permission, then the
1689      *           operation will fail.
1690      *
1691      * @throws  SecurityException
1692      *          If a security manager exists and its <code>{@link
1693      *          java.lang.SecurityManager#checkWrite(java.lang.String)}</code>
1694      *          method denies write access to the file
1695      *
1696      * @since 1.6
1697      */
1698     public boolean setExecutable(boolean executable) {
1699         return setExecutable(executable, true);
1700     }
1701 
1702     /**
1703      * Tests whether the application can execute the file denoted by this
1704      * abstract pathname. On some platforms it may be possible to start the
1705      * Java virtual machine with special privileges that allow it to execute
1706      * files that are not marked executable. Consequently this method may return
1707      * {@code true} even though the file does not have execute permissions.
1708      *
1709      * @return  <code>true</code> if and only if the abstract pathname exists
1710      *          <em>and</em> the application is allowed to execute the file
1711      *
1712      * @throws  SecurityException
1713      *          If a security manager exists and its <code>{@link
1714      *          java.lang.SecurityManager#checkExec(java.lang.String)}</code>
1715      *          method denies execute access to the file
1716      *
1717      * @since 1.6
1718      */
1719     public boolean canExecute() {
1720         SecurityManager security = System.getSecurityManager();
1721         if (security != null) {
1722             security.checkExec(path);
1723         }
1724         if (isInvalid()) {
1725             return false;
1726         }
1727         return fs.checkAccess(this, FileSystem.ACCESS_EXECUTE);
1728     }
1729 
1730 
1731     /* -- Filesystem interface -- */
1732 
1733     /**
1734      * List the available filesystem roots.
1735      *
1736      * <p> A particular Java platform may support zero or more
1737      * hierarchically-organized file systems.  Each file system has a
1738      * {@code root} directory from which all other files in that file system
1739      * can be reached.  Windows platforms, for example, have a root directory
1740      * for each active drive; UNIX platforms have a single root directory,
1741      * namely {@code "/"}.  The set of available filesystem roots is affected
1742      * by various system-level operations such as the insertion or ejection of
1743      * removable media and the disconnecting or unmounting of physical or
1744      * virtual disk drives.
1745      *
1746      * <p> This method returns an array of {@code File} objects that denote the
1747      * root directories of the available filesystem roots.  It is guaranteed
1748      * that the canonical pathname of any file physically present on the local
1749      * machine will begin with one of the roots returned by this method.
1750      *
1751      * <p> The canonical pathname of a file that resides on some other machine
1752      * and is accessed via a remote-filesystem protocol such as SMB or NFS may
1753      * or may not begin with one of the roots returned by this method.  If the
1754      * pathname of a remote file is syntactically indistinguishable from the
1755      * pathname of a local file then it will begin with one of the roots
1756      * returned by this method.  Thus, for example, {@code File} objects
1757      * denoting the root directories of the mapped network drives of a Windows
1758      * platform will be returned by this method, while {@code File} objects
1759      * containing UNC pathnames will not be returned by this method.
1760      *
1761      * <p> Unlike most methods in this class, this method does not throw
1762      * security exceptions.  If a security manager exists and its {@link
1763      * SecurityManager#checkRead(String)} method denies read access to a
1764      * particular root directory, then that directory will not appear in the
1765      * result.
1766      *
1767      * @return  An array of {@code File} objects denoting the available
1768      *          filesystem roots, or {@code null} if the set of roots could not
1769      *          be determined.  The array will be empty if there are no
1770      *          filesystem roots.
1771      *
1772      * @since  1.2
1773      * @see java.nio.file.FileStore
1774      */
1775     public static File[] listRoots() {
1776         return fs.listRoots();
1777     }
1778 
1779 
1780     /* -- Disk usage -- */
1781 
1782     /**
1783      * Returns the size of the partition <a href="#partName">named</a> by this
1784      * abstract pathname.
1785      *
1786      * @return  The size, in bytes, of the partition or <tt>0L</tt> if this
1787      *          abstract pathname does not name a partition
1788      *
1789      * @throws  SecurityException
1790      *          If a security manager has been installed and it denies
1791      *          {@link RuntimePermission}<tt>("getFileSystemAttributes")</tt>
1792      *          or its {@link SecurityManager#checkRead(String)} method denies
1793      *          read access to the file named by this abstract pathname
1794      *
1795      * @since  1.6
1796      */
1797     public long getTotalSpace() {
1798         SecurityManager sm = System.getSecurityManager();
1799         if (sm != null) {
1800             sm.checkPermission(new RuntimePermission("getFileSystemAttributes"));
1801             sm.checkRead(path);
1802         }
1803         if (isInvalid()) {
1804             return 0L;
1805         }
1806         return fs.getSpace(this, FileSystem.SPACE_TOTAL);
1807     }
1808 
1809     /**
1810      * Returns the number of unallocated bytes in the partition <a
1811      * href="#partName">named</a> by this abstract path name.
1812      *
1813      * <p> The returned number of unallocated bytes is a hint, but not
1814      * a guarantee, that it is possible to use most or any of these
1815      * bytes.  The number of unallocated bytes is most likely to be
1816      * accurate immediately after this call.  It is likely to be made
1817      * inaccurate by any external I/O operations including those made
1818      * on the system outside of this virtual machine.  This method
1819      * makes no guarantee that write operations to this file system
1820      * will succeed.
1821      *
1822      * @return  The number of unallocated bytes on the partition or <tt>0L</tt>
1823      *          if the abstract pathname does not name a partition.  This
1824      *          value will be less than or equal to the total file system size
1825      *          returned by {@link #getTotalSpace}.
1826      *
1827      * @throws  SecurityException
1828      *          If a security manager has been installed and it denies
1829      *          {@link RuntimePermission}<tt>("getFileSystemAttributes")</tt>
1830      *          or its {@link SecurityManager#checkRead(String)} method denies
1831      *          read access to the file named by this abstract pathname
1832      *
1833      * @since  1.6
1834      */
1835     public long getFreeSpace() {
1836         SecurityManager sm = System.getSecurityManager();
1837         if (sm != null) {
1838             sm.checkPermission(new RuntimePermission("getFileSystemAttributes"));
1839             sm.checkRead(path);
1840         }
1841         if (isInvalid()) {
1842             return 0L;
1843         }
1844         return fs.getSpace(this, FileSystem.SPACE_FREE);
1845     }
1846 
1847     /**
1848      * Returns the number of bytes available to this virtual machine on the
1849      * partition <a href="#partName">named</a> by this abstract pathname.  When
1850      * possible, this method checks for write permissions and other operating
1851      * system restrictions and will therefore usually provide a more accurate
1852      * estimate of how much new data can actually be written than {@link
1853      * #getFreeSpace}.
1854      *
1855      * <p> The returned number of available bytes is a hint, but not a
1856      * guarantee, that it is possible to use most or any of these bytes.  The
1857      * number of unallocated bytes is most likely to be accurate immediately
1858      * after this call.  It is likely to be made inaccurate by any external
1859      * I/O operations including those made on the system outside of this
1860      * virtual machine.  This method makes no guarantee that write operations
1861      * to this file system will succeed.
1862      *
1863      * @return  The number of available bytes on the partition or <tt>0L</tt>
1864      *          if the abstract pathname does not name a partition.  On
1865      *          systems where this information is not available, this method
1866      *          will be equivalent to a call to {@link #getFreeSpace}.
1867      *
1868      * @throws  SecurityException
1869      *          If a security manager has been installed and it denies
1870      *          {@link RuntimePermission}<tt>("getFileSystemAttributes")</tt>
1871      *          or its {@link SecurityManager#checkRead(String)} method denies
1872      *          read access to the file named by this abstract pathname
1873      *
1874      * @since  1.6
1875      */
1876     public long getUsableSpace() {
1877         SecurityManager sm = System.getSecurityManager();
1878         if (sm != null) {
1879             sm.checkPermission(new RuntimePermission("getFileSystemAttributes"));
1880             sm.checkRead(path);
1881         }
1882         if (isInvalid()) {
1883             return 0L;
1884         }
1885         return fs.getSpace(this, FileSystem.SPACE_USABLE);
1886     }
1887 
1888     /* -- Temporary files -- */
1889 
1890     private static class TempDirectory {
1891         private TempDirectory() { }
1892 
1893         // temporary directory location
1894         private static final File tmpdir = new File(AccessController
1895             .doPrivileged(new GetPropertyAction("java.io.tmpdir")));
1896         static File location() {
1897             return tmpdir;
1898         }
1899 
1900         // file name generation
1901         private static final SecureRandom random = new SecureRandom();
1902         static File generateFile(String prefix, String suffix, File dir)
1903             throws IOException
1904         {
1905             long n = random.nextLong();
1906             if (n == Long.MIN_VALUE) {
1907                 n = 0;      // corner case
1908             } else {
1909                 n = Math.abs(n);
1910             }
1911 
1912             // Use only the file name from the supplied prefix
1913             prefix = (new File(prefix)).getName();
1914 
1915             String name = prefix + Long.toString(n) + suffix;
1916             File f = new File(dir, name);
1917             if (!name.equals(f.getName()) || f.isInvalid()) {
1918                 if (System.getSecurityManager() != null)
1919                     throw new IOException("Unable to create temporary file");
1920                 else
1921                     throw new IOException("Unable to create temporary file, " + f);
1922             }
1923             return f;
1924         }
1925     }
1926 
1927     /**
1928      * <p> Creates a new empty file in the specified directory, using the
1929      * given prefix and suffix strings to generate its name.  If this method
1930      * returns successfully then it is guaranteed that:
1931      *
1932      * <ol>
1933      * <li> The file denoted by the returned abstract pathname did not exist
1934      *      before this method was invoked, and
1935      * <li> Neither this method nor any of its variants will return the same
1936      *      abstract pathname again in the current invocation of the virtual
1937      *      machine.
1938      * </ol>
1939      *
1940      * This method provides only part of a temporary-file facility.  To arrange
1941      * for a file created by this method to be deleted automatically, use the
1942      * <code>{@link #deleteOnExit}</code> method.
1943      *
1944      * <p> The <code>prefix</code> argument must be at least three characters
1945      * long.  It is recommended that the prefix be a short, meaningful string
1946      * such as <code>"hjb"</code> or <code>"mail"</code>.  The
1947      * <code>suffix</code> argument may be <code>null</code>, in which case the
1948      * suffix <code>".tmp"</code> will be used.
1949      *
1950      * <p> To create the new file, the prefix and the suffix may first be
1951      * adjusted to fit the limitations of the underlying platform.  If the
1952      * prefix is too long then it will be truncated, but its first three
1953      * characters will always be preserved.  If the suffix is too long then it
1954      * too will be truncated, but if it begins with a period character
1955      * (<code>'.'</code>) then the period and the first three characters
1956      * following it will always be preserved.  Once these adjustments have been
1957      * made the name of the new file will be generated by concatenating the
1958      * prefix, five or more internally-generated characters, and the suffix.
1959      *
1960      * <p> If the <code>directory</code> argument is <code>null</code> then the
1961      * system-dependent default temporary-file directory will be used.  The
1962      * default temporary-file directory is specified by the system property
1963      * <code>java.io.tmpdir</code>.  On UNIX systems the default value of this
1964      * property is typically <code>"/tmp"</code> or <code>"/var/tmp"</code>; on
1965      * Microsoft Windows systems it is typically <code>"C:\\WINNT\\TEMP"</code>.  A different
1966      * value may be given to this system property when the Java virtual machine
1967      * is invoked, but programmatic changes to this property are not guaranteed
1968      * to have any effect upon the temporary directory used by this method.
1969      *
1970      * @param  prefix     The prefix string to be used in generating the file's
1971      *                    name; must be at least three characters long
1972      *
1973      * @param  suffix     The suffix string to be used in generating the file's
1974      *                    name; may be <code>null</code>, in which case the
1975      *                    suffix <code>".tmp"</code> will be used
1976      *
1977      * @param  directory  The directory in which the file is to be created, or
1978      *                    <code>null</code> if the default temporary-file
1979      *                    directory is to be used
1980      *
1981      * @return  An abstract pathname denoting a newly-created empty file
1982      *
1983      * @throws  IllegalArgumentException
1984      *          If the <code>prefix</code> argument contains fewer than three
1985      *          characters
1986      *
1987      * @throws  IOException  If a file could not be created
1988      *
1989      * @throws  SecurityException
1990      *          If a security manager exists and its <code>{@link
1991      *          java.lang.SecurityManager#checkWrite(java.lang.String)}</code>
1992      *          method does not allow a file to be created
1993      *
1994      * @since 1.2
1995      */
1996     public static File createTempFile(String prefix, String suffix,
1997                                       File directory)
1998         throws IOException
1999     {
2000         if (prefix.length() < 3)
2001             throw new IllegalArgumentException("Prefix string too short");
2002         if (suffix == null)
2003             suffix = ".tmp";
2004 
2005         File tmpdir = (directory != null) ? directory
2006                                           : TempDirectory.location();
2007         SecurityManager sm = System.getSecurityManager();
2008         File f;
2009         do {
2010             f = TempDirectory.generateFile(prefix, suffix, tmpdir);
2011 
2012             if (sm != null) {
2013                 try {
2014                     sm.checkWrite(f.getPath());
2015                 } catch (SecurityException se) {
2016                     // don't reveal temporary directory location
2017                     if (directory == null)
2018                         throw new SecurityException("Unable to create temporary file");
2019                     throw se;
2020                 }
2021             }
2022         } while ((fs.getBooleanAttributes(f) & FileSystem.BA_EXISTS) != 0);
2023 
2024         if (!fs.createFileExclusively(f.getPath()))
2025             throw new IOException("Unable to create temporary file");
2026 
2027         return f;
2028     }
2029 
2030     /**
2031      * Creates an empty file in the default temporary-file directory, using
2032      * the given prefix and suffix to generate its name. Invoking this method
2033      * is equivalent to invoking <code>{@link #createTempFile(java.lang.String,
2034      * java.lang.String, java.io.File)
2035      * createTempFile(prefix,&nbsp;suffix,&nbsp;null)}</code>.
2036      *
2037      * <p> The {@link
2038      * java.nio.file.Files#createTempFile(String,String,java.nio.file.attribute.FileAttribute[])
2039      * Files.createTempFile} method provides an alternative method to create an
2040      * empty file in the temporary-file directory. Files created by that method
2041      * may have more restrictive access permissions to files created by this
2042      * method and so may be more suited to security-sensitive applications.
2043      *
2044      * @param  prefix     The prefix string to be used in generating the file's
2045      *                    name; must be at least three characters long
2046      *
2047      * @param  suffix     The suffix string to be used in generating the file's
2048      *                    name; may be <code>null</code>, in which case the
2049      *                    suffix <code>".tmp"</code> will be used
2050      *
2051      * @return  An abstract pathname denoting a newly-created empty file
2052      *
2053      * @throws  IllegalArgumentException
2054      *          If the <code>prefix</code> argument contains fewer than three
2055      *          characters
2056      *
2057      * @throws  IOException  If a file could not be created
2058      *
2059      * @throws  SecurityException
2060      *          If a security manager exists and its <code>{@link
2061      *          java.lang.SecurityManager#checkWrite(java.lang.String)}</code>
2062      *          method does not allow a file to be created
2063      *
2064      * @since 1.2
2065      * @see java.nio.file.Files#createTempDirectory(String,FileAttribute[])
2066      */
2067     public static File createTempFile(String prefix, String suffix)
2068         throws IOException
2069     {
2070         return createTempFile(prefix, suffix, null);
2071     }
2072 
2073     /* -- Basic infrastructure -- */
2074 
2075     /**
2076      * Compares two abstract pathnames lexicographically.  The ordering
2077      * defined by this method depends upon the underlying system.  On UNIX
2078      * systems, alphabetic case is significant in comparing pathnames; on Microsoft Windows
2079      * systems it is not.
2080      *
2081      * @param   pathname  The abstract pathname to be compared to this abstract
2082      *                    pathname
2083      *
2084      * @return  Zero if the argument is equal to this abstract pathname, a
2085      *          value less than zero if this abstract pathname is
2086      *          lexicographically less than the argument, or a value greater
2087      *          than zero if this abstract pathname is lexicographically
2088      *          greater than the argument
2089      *
2090      * @since   1.2
2091      */
2092     public int compareTo(File pathname) {
2093         return fs.compare(this, pathname);
2094     }
2095 
2096     /**
2097      * Tests this abstract pathname for equality with the given object.
2098      * Returns <code>true</code> if and only if the argument is not
2099      * <code>null</code> and is an abstract pathname that denotes the same file
2100      * or directory as this abstract pathname.  Whether or not two abstract
2101      * pathnames are equal depends upon the underlying system.  On UNIX
2102      * systems, alphabetic case is significant in comparing pathnames; on Microsoft Windows
2103      * systems it is not.
2104      *
2105      * @param   obj   The object to be compared with this abstract pathname
2106      *
2107      * @return  <code>true</code> if and only if the objects are the same;
2108      *          <code>false</code> otherwise
2109      */
2110     public boolean equals(Object obj) {
2111         if ((obj != null) && (obj instanceof File)) {
2112             return compareTo((File)obj) == 0;
2113         }
2114         return false;
2115     }
2116 
2117     /**
2118      * Computes a hash code for this abstract pathname.  Because equality of
2119      * abstract pathnames is inherently system-dependent, so is the computation
2120      * of their hash codes.  On UNIX systems, the hash code of an abstract
2121      * pathname is equal to the exclusive <em>or</em> of the hash code
2122      * of its pathname string and the decimal value
2123      * <code>1234321</code>.  On Microsoft Windows systems, the hash
2124      * code is equal to the exclusive <em>or</em> of the hash code of
2125      * its pathname string converted to lower case and the decimal
2126      * value <code>1234321</code>.  Locale is not taken into account on
2127      * lowercasing the pathname string.
2128      *
2129      * @return  A hash code for this abstract pathname
2130      */
2131     public int hashCode() {
2132         return fs.hashCode(this);
2133     }
2134 
2135     /**
2136      * Returns the pathname string of this abstract pathname.  This is just the
2137      * string returned by the <code>{@link #getPath}</code> method.
2138      *
2139      * @return  The string form of this abstract pathname
2140      */
2141     public String toString() {
2142         return getPath();
2143     }
2144 
2145     /**
2146      * WriteObject is called to save this filename.
2147      * The separator character is saved also so it can be replaced
2148      * in case the path is reconstituted on a different host type.
2149      * <p>
2150      * @serialData  Default fields followed by separator character.
2151      */
2152     private synchronized void writeObject(java.io.ObjectOutputStream s)
2153         throws IOException
2154     {
2155         s.defaultWriteObject();
2156         s.writeChar(separatorChar); // Add the separator character
2157     }
2158 
2159     /**
2160      * readObject is called to restore this filename.
2161      * The original separator character is read.  If it is different
2162      * than the separator character on this system, then the old separator
2163      * is replaced by the local separator.
2164      */
2165     private synchronized void readObject(java.io.ObjectInputStream s)
2166          throws IOException, ClassNotFoundException
2167     {
2168         ObjectInputStream.GetField fields = s.readFields();
2169         String pathField = (String)fields.get("path", null);
2170         char sep = s.readChar(); // read the previous separator char
2171         if (sep != separatorChar)
2172             pathField = pathField.replace(sep, separatorChar);
2173         String path = fs.normalize(pathField);
2174         UNSAFE.putObject(this, PATH_OFFSET, path);
2175         UNSAFE.putIntVolatile(this, PREFIX_LENGTH_OFFSET, fs.prefixLength(path));
2176     }
2177 
2178     private static final long PATH_OFFSET;
2179     private static final long PREFIX_LENGTH_OFFSET;
2180     private static final sun.misc.Unsafe UNSAFE;
2181     static {
2182         try {
2183             sun.misc.Unsafe unsafe = sun.misc.Unsafe.getUnsafe();
2184             PATH_OFFSET = unsafe.objectFieldOffset(
2185                     File.class.getDeclaredField("path"));
2186             PREFIX_LENGTH_OFFSET = unsafe.objectFieldOffset(
2187                     File.class.getDeclaredField("prefixLength"));
2188             UNSAFE = unsafe;
2189         } catch (ReflectiveOperationException e) {
2190             throw new Error(e);
2191         }
2192     }
2193 
2194 
2195     /** use serialVersionUID from JDK 1.0.2 for interoperability */
2196     private static final long serialVersionUID = 301077366599181567L;
2197 
2198     // -- Integration with java.nio.file --
2199 
2200     private volatile transient Path filePath;
2201 
2202     /**
2203      * Returns a {@link Path java.nio.file.Path} object constructed from the
2204      * this abstract path. The resulting {@code Path} is associated with the
2205      * {@link java.nio.file.FileSystems#getDefault default-filesystem}.
2206      *
2207      * <p> The first invocation of this method works as if invoking it were
2208      * equivalent to evaluating the expression:
2209      * <blockquote><pre>
2210      * {@link java.nio.file.FileSystems#getDefault FileSystems.getDefault}().{@link
2211      * java.nio.file.FileSystem#getPath getPath}(this.{@link #getPath getPath}());
2212      * </pre></blockquote>
2213      * Subsequent invocations of this method return the same {@code Path}.
2214      *
2215      * <p> If this abstract pathname is the empty abstract pathname then this
2216      * method returns a {@code Path} that may be used to access the current
2217      * user directory.
2218      *
2219      * @return  a {@code Path} constructed from this abstract path
2220      *
2221      * @throws  java.nio.file.InvalidPathException
2222      *          if a {@code Path} object cannot be constructed from the abstract
2223      *          path (see {@link java.nio.file.FileSystem#getPath FileSystem.getPath})
2224      *
2225      * @since   1.7
2226      * @see Path#toFile
2227      */
2228     public Path toPath() {
2229         Path result = filePath;
2230         if (result == null) {
2231             synchronized (this) {
2232                 result = filePath;
2233                 if (result == null) {
2234                     result = FileSystems.getDefault().getPath(path);
2235                     filePath = result;
2236                 }
2237             }
2238         }
2239         return result;
2240     }
2241 }