/*

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 * @deprecated This class has been replaced by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

    }

}