/* * 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 * * @deprecated This class has been replaced by * 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);    } }