/*
* @(#)Ref.java 1.35 06/10/10
*
* Copyright 1990-2008 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER
*
* This program 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.
*
* This program 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 at /legal/license.txt).
*
* 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 Sun Microsystems, Inc., 4150 Network Circle, Santa
* Clara, CA 95054 or visit www.sun.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* @deprecated This class has been replaced by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
*
* @version 1.35, 10/10/06
*/
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);
}
}