001: package com.protomatter.util;
002:
003: /**
004: * {{{ The Protomatter Software License, Version 1.0
005: * derived from The Apache Software License, Version 1.1
006: *
007: * Copyright (c) 1998-2002 Nate Sammons. All rights reserved.
008: *
009: * Redistribution and use in source and binary forms, with or without
010: * modification, are permitted provided that the following conditions
011: * are met:
012: *
013: * 1. Redistributions of source code must retain the above copyright
014: * notice, this list of conditions and the following disclaimer.
015: *
016: * 2. Redistributions in binary form must reproduce the above copyright
017: * notice, this list of conditions and the following disclaimer in
018: * the documentation and/or other materials provided with the
019: * distribution.
020: *
021: * 3. The end-user documentation included with the redistribution,
022: * if any, must include the following acknowledgment:
023: * "This product includes software developed for the
024: * Protomatter Software Project
025: * (http://protomatter.sourceforge.net/)."
026: * Alternately, this acknowledgment may appear in the software itself,
027: * if and wherever such third-party acknowledgments normally appear.
028: *
029: * 4. The names "Protomatter" and "Protomatter Software Project" must
030: * not be used to endorse or promote products derived from this
031: * software without prior written permission. For written
032: * permission, please contact support@protomatter.com.
033: *
034: * 5. Products derived from this software may not be called "Protomatter",
035: * nor may "Protomatter" appear in their name, without prior written
036: * permission of the Protomatter Software Project
037: * (support@protomatter.com).
038: *
039: * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
040: * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
041: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
042: * DISCLAIMED. IN NO EVENT SHALL THE PROTOMATTER SOFTWARE PROJECT OR
043: * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
044: * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
045: * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
046: * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
047: * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
048: * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
049: * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
050: * SUCH DAMAGE. }}}
051: */
052:
053: import java.util.*;
054: import java.lang.ref.*;
055:
056: /**
057: * A cache that uses soft references. Values in this cache
058: * are expired by the VM in reponse to memory needs. For
059: * more information on how this works, see the JavaDoc
060: * for the <TT>java.lang.ref</TT> package.
061: */
062: public class SoftReferenceCache implements Cache {
063: private Map map = null;
064:
065: /**
066: * Create a new cache.
067: */
068: public SoftReferenceCache() {
069: clear();
070: }
071:
072: /**
073: * Put a value into the cache, possibly clobbering
074: * the old value if one exists.
075: */
076: public void put(Object key, Object val) {
077: map.put(key, new SoftReference(val));
078: }
079:
080: /**
081: * Get a value from the cache at the given key.
082: *
083: * @return The cached value, or <TT>null</TT> if no value exists.
084: */
085: public Object get(Object key) {
086: SoftReference ref = (SoftReference) map.get(key);
087: if (ref != null) {
088: Object o = ref.get();
089: if (o == null)
090: clear(key);
091: return o;
092: }
093: return null;
094: }
095:
096: /**
097: * Clear the value in the cache at the given key.
098: */
099: public void clear(Object key) {
100: this .map.remove(key);
101: }
102:
103: /**
104: * Clear the entire cache.
105: */
106: public void clear() {
107: this .map = new HashMap();
108: }
109: }
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