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