1 /* VMString.java -- VM Specific String methods
2 Copyright (C) 2003 Free Software Foundation
3
4 This file is part of GNU Classpath.
5
6 GNU Classpath is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2, or (at your option)
9 any later version.
10
11 GNU Classpath is distributed in the hope that it will be useful, but
12 WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 General Public License for more details.
15
16 You should have received a copy of the GNU General Public License
17 along with GNU Classpath; see the file COPYING. If not, write to the
18 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
19 02110-1301 USA.
20
21 Linking this library statically or dynamically with other modules is
22 making a combined work based on this library. Thus, the terms and
23 conditions of the GNU General Public License cover the whole
24 combination.
25
26 As a special exception, the copyright holders of this library give you
27 permission to link this library with independent modules to produce an
28 executable, regardless of the license terms of these independent
29 modules, and to copy and distribute the resulting executable under
30 terms of your choice, provided that you also meet, for each linked
31 independent module, the terms and conditions of the license of that
32 module. An independent module is a module which is not derived from
33 or based on this library. If you modify this library, you may extend
34 this exception to your version of the library, but you are not
35 obligated to do so. If you do not wish to do so, delete this
36 exception statement from your version. */
37
38 package java.lang;
39
40 import java.lang.ref.WeakReference;
41 import java.util.WeakHashMap;
42
43 /*
44 * This class is a reference version, mainly for compiling a class library
45 * jar. It is likely that VM implementers replace this with their own
46 * version that can communicate effectively with the VM.
47 */
48
49 /**
50 * Code relocated from java.lang.String by
51 * @author Dave Grove <groved@us.ibm.com>
52 */
53 final class VMString
54 {
55
56 /**
57 * Holds the references for each intern()'d String. If all references to
58 * the string disappear, and the VM properly supports weak references,
59 * the String will be GC'd.
60 */
61 private static final WeakHashMap internTable = new WeakHashMap();
62
63 /**
64 * Fetches this String from the intern hashtable. If two Strings are
65 * considered equal, by the equals() method, then intern() will return the
66 * same String instance. ie. if (s1.equals(s2)) then
67 * (s1.intern() == s2.intern()). All string literals and string-valued
68 * constant expressions are already interned.
69 *
70 * @param str the String to intern
71 * @return the interned String
72 */
73 static String intern(String str)
74 {
75 synchronized (internTable)
76 {
77 WeakReference ref = (WeakReference) internTable.get(str);
78 if (ref != null)
79 {
80 String s = (String) ref.get();
81 // If s is null, then no strong references exist to the String;
82 // the weak hash map will soon delete the key.
83 if (s != null)
84 return s;
85 }
86 internTable.put(str, new WeakReference(str));
87 }
88 return str;
89 }
90
91 } // class VMString
Save This Page