Showing the changes to java/pkg/sun/misc/Ref.java (1 of 18352 files). Show all
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| 1 | +/* | |
| 2 | + * Copyright (c) 1995, 2004, 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 sun.misc; | |
| 27 | +import java.lang.ref.SoftReference; | |
| 28 | + | |
| 29 | + | |
| 30 | +/** | |
| 31 | + * A "Ref" is an indirect reference to an object that the garbage collector | |
| 32 | + * knows about. An application should override the reconstitute() method with one | |
| 33 | + * that will construct the object based on information in the Ref, often by | |
| 34 | + * reading from a file. The get() method retains a cache of the result of the last call to | |
| 35 | + * reconstitute() in the Ref. When space gets tight, the garbage collector | |
| 36 | + * will clear old Ref cache entries when there are no other pointers to the | |
| 37 | + * object. In normal usage, Ref will always be subclassed. The subclass will add the | |
| 38 | + * instance variables necessary for the reconstitute() method to work. It will also add a | |
| 39 | + * constructor to set them up, and write a version of reconstitute(). | |
| 40 | + * | |
| 41 | + * @deprecated This class has been replaced by | |
| 42 | + * <code>java.util.SoftReference</code>. | |
| 43 | + * | |
| 44 | + * @see java.util.SoftReference | |
| 45 | + * | |
| 46 | + */ | |
| 47 | +@Deprecated | |
| 48 | + | |
| 49 | +public abstract class Ref { | |
| 50 | + | |
| 51 | + private SoftReference soft = null; | |
| 52 | + | |
| 53 | + /** | |
| 54 | + * Returns a pointer to the object referenced by this Ref. If the object | |
| 55 | + * has been thrown away by the garbage collector, it will be | |
| 56 | + * reconstituted. This method does everything necessary to ensure that the garbage | |
| 57 | + * collector throws things away in Least Recently Used(LRU) order. Applications should | |
| 58 | + * never override this method. The get() method effectively caches calls to | |
| 59 | + * reconstitute(). | |
| 60 | + */ | |
| 61 | + public synchronized Object get() { | |
| 62 | + Object t = check(); | |
| 63 | + if (t == null) { | |
| 64 | + t = reconstitute(); | |
| 65 | + setThing(t); | |
| 66 | + } | |
| 67 | + return t; | |
| 68 | + } | |
| 69 | + | |
| 70 | + /** | |
| 71 | + * Returns a pointer to the object referenced by this Ref by | |
| 72 | + * reconstituting it from some external source (such as a file). This method should not | |
| 73 | + * bother with caching since the method get() will deal with that. | |
| 74 | + * <p> | |
| 75 | + * In normal usage, Ref will always be subclassed. The subclass will add | |
| 76 | + * the instance variables necessary for reconstitute() to work. It will | |
| 77 | + * also add a constructor to set them up, and write a version of | |
| 78 | + * reconstitute(). | |
| 79 | + */ | |
| 80 | + public abstract Object reconstitute(); | |
| 81 | + | |
| 82 | + /** | |
| 83 | + * Flushes the cached object. Forces the next invocation of get() to | |
| 84 | + * invoke reconstitute(). | |
| 85 | + */ | |
| 86 | + public synchronized void flush() { | |
| 87 | + SoftReference s = soft; | |
| 88 | + if (s != null) s.clear(); | |
| 89 | + soft = null; | |
| 90 | + } | |
| 91 | + | |
| 92 | + /** | |
| 93 | + * Sets the thing to the specified object. | |
| 94 | + * @param thing the specified object | |
| 95 | + */ | |
| 96 | + public synchronized void setThing(Object thing) { | |
| 97 | + flush(); | |
| 98 | + soft = new SoftReference(thing); | |
| 99 | + } | |
| 100 | + | |
| 101 | + /** | |
| 102 | + * Checks to see what object is being pointed at by this Ref and returns it. | |
| 103 | + */ | |
| 104 | + public synchronized Object check() { | |
| 105 | + SoftReference s = soft; | |
| 106 | + if (s == null) return null; | |
| 107 | + return s.get(); | |
| 108 | + } | |
| 109 | + | |
| 110 | + /** | |
| 111 | + * Constructs a new Ref. | |
| 112 | + */ | |
| 113 | + public Ref() { } | |
| 114 | + | |
| 115 | + /** | |
| 116 | + * Constructs a new Ref that initially points to thing. | |
| 117 | + */ | |
| 118 | + public Ref(Object thing) { | |
| 119 | + setThing(thing); | |
| 120 | + } | |
| 121 | + | |
| 122 | +} | |