| /* |
| * Copyright (c) 1995, 2004, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| package sun.misc; |
| import java.lang.ref.SoftReference; |
| |
| |
| /** |
| * A "Ref" is an indirect reference to an object that the garbage collector |
| * knows about. An application should override the reconstitute() method with one |
| * that will construct the object based on information in the Ref, often by |
| * reading from a file. The get() method retains a cache of the result of the last call to |
| * reconstitute() in the Ref. When space gets tight, the garbage collector |
| * will clear old Ref cache entries when there are no other pointers to the |
| * object. In normal usage, Ref will always be subclassed. The subclass will add the |
| * instance variables necessary for the reconstitute() method to work. It will also add a |
| * constructor to set them up, and write a version of reconstitute(). |
| * |
| * @deprecated This class has been replaced by |
| * <code>java.util.SoftReference</code>. |
| * |
| * @see java.util.SoftReference |
| * |
| */ |
| @Deprecated |
| |
| public abstract class Ref { |
| |
| private SoftReference soft = null; |
| |
| /** |
| * Returns a pointer to the object referenced by this Ref. If the object |
| * has been thrown away by the garbage collector, it will be |
| * reconstituted. This method does everything necessary to ensure that the garbage |
| * collector throws things away in Least Recently Used(LRU) order. Applications should |
| * never override this method. The get() method effectively caches calls to |
| * reconstitute(). |
| */ |
| public synchronized Object get() { |
| Object t = check(); |
| if (t == null) { |
| t = reconstitute(); |
| setThing(t); |
| } |
| return t; |
| } |
| |
| /** |
| * Returns a pointer to the object referenced by this Ref by |
| * reconstituting it from some external source (such as a file). This method should not |
| * bother with caching since the method get() will deal with that. |
| * <p> |
| * In normal usage, Ref will always be subclassed. The subclass will add |
| * the instance variables necessary for reconstitute() to work. It will |
| * also add a constructor to set them up, and write a version of |
| * reconstitute(). |
| */ |
| public abstract Object reconstitute(); |
| |
| /** |
| * Flushes the cached object. Forces the next invocation of get() to |
| * invoke reconstitute(). |
| */ |
| public synchronized void flush() { |
| SoftReference s = soft; |
| if (s != null) s.clear(); |
| soft = null; |
| } |
| |
| /** |
| * Sets the thing to the specified object. |
| * @param thing the specified object |
| */ |
| public synchronized void setThing(Object thing) { |
| flush(); |
| soft = new SoftReference(thing); |
| } |
| |
| /** |
| * Checks to see what object is being pointed at by this Ref and returns it. |
| */ |
| public synchronized Object check() { |
| SoftReference s = soft; |
| if (s == null) return null; |
| return s.get(); |
| } |
| |
| /** |
| * Constructs a new Ref. |
| */ |
| public Ref() { } |
| |
| /** |
| * Constructs a new Ref that initially points to thing. |
| */ |
| public Ref(Object thing) { |
| setThing(thing); |
| } |
| |
| } |