Source Code Cross Referenced for Ref.java in  » 6.0-JDK-Modules » j2me » sun » misc » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » 6.0 JDK Modules » j2me » sun.misc 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         * @(#)Ref.java	1.35 06/10/10
003:         *
004:         * Copyright  1990-2006 Sun Microsystems, Inc. All Rights Reserved.
005:         * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER
006:         * 
007:         * This program is free software; you can redistribute it and/or
008:         * modify it under the terms of the GNU General Public License version
009:         * 2 only, as published by the Free Software Foundation. 
010:         * 
011:         * This program is distributed in the hope that it will be useful, but
012:         * WITHOUT ANY WARRANTY; without even the implied warranty of
013:         * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
014:         * General Public License version 2 for more details (a copy is
015:         * included at /legal/license.txt). 
016:         * 
017:         * You should have received a copy of the GNU General Public License
018:         * version 2 along with this work; if not, write to the Free Software
019:         * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
020:         * 02110-1301 USA 
021:         * 
022:         * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa
023:         * Clara, CA 95054 or visit www.sun.com if you need additional
024:         * information or have any questions. 
025:         */
026:
027:        package sun.misc;
028:
029:        import java.lang.ref.SoftReference;
030:
031:        /**
032:         * A "Ref" is an indirect reference to an object that the garbage collector
033:         * knows about.  An application should override the reconstitute() method with one
034:         * that will construct the object based on information in the Ref, often by
035:         * reading from a file.  The get() method retains a cache of the result of the last call to
036:         * reconstitute() in the Ref.  When space gets tight, the garbage collector
037:         * will clear old Ref cache entries when there are no other pointers to the
038:         * object.  In normal usage, Ref will always be subclassed.  The subclass will add the 
039:         * instance variables necessary for the reconstitute() method to work.  It will also add a 
040:         * constructor to set them up, and write a version of reconstitute().
041:         *
042:         * @deprecated This class has been replaced by
043:         * <code>java.util.SoftReference</code>.
044:         *
045:         * @see java.util.SoftReference
046:         *
047:         * @version     1.35, 10/10/06
048:         */
049:
050:        public abstract class Ref {
051:
052:            private SoftReference soft = null;
053:
054:            /**
055:             * Returns a pointer to the object referenced by this Ref.  If the object
056:             * has been thrown away by the garbage collector, it will be
057:             * reconstituted. This method does everything necessary to ensure that the garbage
058:             * collector throws things away in Least Recently Used(LRU) order.  Applications should 
059:             * never override this method. The get() method effectively caches calls to
060:             * reconstitute().
061:             */
062:            public synchronized Object get() {
063:                Object t = check();
064:                if (t == null) {
065:                    t = reconstitute();
066:                    setThing(t);
067:                }
068:                return t;
069:            }
070:
071:            /**
072:             * Returns a pointer to the object referenced by this Ref by 
073:             * reconstituting it from some external source (such as a file).  This method should not 
074:             * bother with caching since the method get() will deal with that.
075:             * <p>
076:             * In normal usage, Ref will always be subclassed.  The subclass will add
077:             * the instance variables necessary for reconstitute() to work.  It will
078:             * also add a constructor to set them up, and write a version of
079:             * reconstitute().
080:             */
081:            public abstract Object reconstitute();
082:
083:            /**
084:             * Flushes the cached object.  Forces the next invocation of get() to
085:             * invoke reconstitute().
086:             */
087:            public synchronized void flush() {
088:                SoftReference s = soft;
089:                if (s != null)
090:                    s.clear();
091:                soft = null;
092:            }
093:
094:            /**
095:             * Sets the thing to the specified object.
096:             * @param thing the specified object
097:             */
098:            public synchronized void setThing(Object thing) {
099:                flush();
100:                soft = new SoftReference(thing);
101:            }
102:
103:            /**
104:             * Checks to see what object is being pointed at by this Ref and returns it.
105:             */
106:            public synchronized Object check() {
107:                SoftReference s = soft;
108:                if (s == null)
109:                    return null;
110:                return s.get();
111:            }
112:
113:            /**
114:             * Constructs a new Ref.
115:             */
116:            public Ref() {
117:            }
118:
119:            /**
120:             * Constructs a new Ref that initially points to thing.
121:             */
122:            public Ref(Object thing) {
123:                setThing(thing);
124:            }
125:
126:        }
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