Source Code Cross Referenced for SoftHashMap.java in  » Profiler » JMeasurement » de » mcs » utils » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Profiler » JMeasurement » de.mcs.utils 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         * MCS Media Computer Software Copyright (c) 2005 by MCS
003:         * -------------------------------------- Created on 23.04.2005 by w.klaas
004:         * 
005:         * Licensed under the Apache License, Version 2.0 (the "License"); you may not
006:         * use this file except in compliance with the License. You may obtain a copy of
007:         * the License at
008:         * 
009:         * http://www.apache.org/licenses/LICENSE-2.0
010:         * 
011:         * Unless required by applicable law or agreed to in writing, software
012:         * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
013:         * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
014:         * License for the specific language governing permissions and limitations under
015:         * the License.
016:         */
017:        package de.mcs.utils;
018:
019:        import java.lang.ref.Reference;
020:        import java.lang.ref.ReferenceQueue;
021:        import java.lang.ref.SoftReference;
022:        import java.util.AbstractMap;
023:        import java.util.AbstractSet;
024:        import java.util.HashMap;
025:        import java.util.Iterator;
026:        import java.util.Map;
027:        import java.util.NoSuchElementException;
028:        import java.util.Set;
029:
030:        /**
031:         * Implements a Map with only soft references backuped by a hashmap.
032:         * 
033:         * @author w.klaas
034:         */
035:
036:        public class SoftHashMap extends AbstractMap {
037:            /** the map to store. */
038:            private Map m = null;
039:
040:            /** the reference queue. */
041:            private ReferenceQueue q = new ReferenceQueue();
042:
043:            /**
044:             * Constructs an empty <tt>HashMap</tt> with the default initial capacity
045:             * (16) and the default load factor (0.75).
046:             */
047:            public SoftHashMap() {
048:                m = new HashMap();
049:            }
050:
051:            /**
052:             * Constructs an empty <tt>HashMap</tt> with the specified initial
053:             * capacity and the default load factor (0.75).
054:             * 
055:             * @param initialCapacity
056:             *            the initial capacity.
057:             */
058:            public SoftHashMap(final int initialCapacity) {
059:                m = new HashMap(initialCapacity);
060:            }
061:
062:            /**
063:             * Constructs an empty <tt>HashMap</tt> with the specified initial
064:             * capacity and load factor.
065:             * 
066:             * @param initialCapacity
067:             *            The initial capacity.
068:             * @param loadFactor
069:             *            The load factor.
070:             */
071:            public SoftHashMap(final int initialCapacity, final float loadFactor) {
072:                m = new HashMap(initialCapacity, loadFactor);
073:            }
074:
075:            /**
076:             * Returns the value to which this map maps the specified key. Returns
077:             * <tt>null</tt> if the map contains no mapping for this key. A return
078:             * value of <tt>null</tt> does not <i>necessarily</i> indicate that the
079:             * map contains no mapping for the key; it's also possible that the map
080:             * explicitly maps the key to <tt>null</tt>. The <tt>containsKey</tt>
081:             * operation may be used to distinguish these two cases.
082:             * 
083:             * <p>
084:             * More formally, if this map contains a mapping from a key <tt>k</tt> to
085:             * a value <tt>v</tt> such that <tt>(key==null ? k==null :
086:             * key.equals(k))</tt>,
087:             * then this method returns <tt>v</tt>; otherwise it returns
088:             * <tt>null</tt>. (There can be at most one such mapping.)
089:             * 
090:             * @param key
091:             *            key whose associated value is to be returned.
092:             * @return the value to which this map maps the specified key, or
093:             *         <tt>null</tt> if the map contains no mapping for this key.
094:             * 
095:             * @see #containsKey(Object)
096:             */
097:            public final Object get(final Object key) {
098:                Object res = m.get(key);
099:                return res == null ? null : ((Reference) res).get();
100:            }
101:
102:            /**
103:             * @see Map#put(K, V)
104:             */
105:            public final Object put(final Object key, final Object value) {
106:                processQueue();
107:                Reference ref = new SoftEntry(key, value, q);
108:                Object res = m.put(key, ref);
109:                return res == null ? null : ((Reference) res).get();
110:            }
111:
112:            /** the entry set. */
113:            private Set entrySet = null;
114:
115:            /**
116:             * getting the entry set.
117:             * 
118:             * @return Set
119:             */
120:            public final Set entrySet() {
121:                if (entrySet == null) {
122:                    entrySet = new EntrySet();
123:                }
124:                return entrySet;
125:            }
126:
127:            /**
128:             * processing the softentry queue.
129:             * 
130:             */
131:            private void processQueue() {
132:                Reference r;
133:                while ((r = q.poll()) != null) {
134:                    SoftEntry e = (SoftEntry) r;
135:                    m.remove(e.key);
136:                }
137:            }
138:
139:            /**
140:             * @see java.util.Set#size()
141:             */
142:            public final int size() {
143:                return entrySet().size();
144:            }
145:
146:            /**
147:             * @see java.util.Set#remove(java.lang.Object)
148:             */
149:            public final Object remove(final Object key) {
150:                processQueue();
151:                Object res = m.remove(key);
152:                return res == null ? null : ((Reference) res).get();
153:            }
154:
155:            /**
156:             * @see java.util.Map#clear()
157:             */
158:            public final void clear() {
159:                processQueue();
160:                m.clear();
161:            }
162:
163:            /**
164:             * this is the soft reference entry in the map.
165:             * 
166:             * @author w.klaas
167:             * 
168:             */
169:            private static final class SoftEntry extends SoftReference {
170:                /** neccessary so that freed objects can be removed. */
171:                private Object key;
172:
173:                /**
174:                 * private contructor to this entry.
175:                 * 
176:                 * @param aKey
177:                 *            the key for this entry
178:                 * @param value
179:                 *            the value
180:                 * @param q
181:                 *            the reference queue
182:                 */
183:                private SoftEntry(final Object aKey, final Object value,
184:                        final ReferenceQueue q) {
185:                    super (value, q);
186:                    this .key = aKey;
187:                }
188:            }
189:
190:            /**
191:             * My set of entries.
192:             * 
193:             * @author w.klaas
194:             * 
195:             */
196:            private class EntrySet extends AbstractSet {
197:                /** the entry set to use. */
198:                private Set entrySet = m.entrySet();
199:
200:                /**
201:                 * @see java.util.Set#size()
202:                 */
203:                public int size() {
204:                    int s = 0;
205:                    for (Iterator i = iterator(); i.hasNext(); i.next()) {
206:                        s++;
207:                    }
208:                    return s;
209:                }
210:
211:                /**
212:                 * @see java.util.Set#isEmpty()
213:                 */
214:                public boolean isEmpty() {
215:                    return !(iterator().hasNext());
216:                }
217:
218:                /**
219:                 * @see java.util.Set#remove(java.lang.Object)
220:                 */
221:                public boolean remove(final Object o) {
222:                    processQueue();
223:                    return super .remove(o);
224:                }
225:
226:                /**
227:                 * @see java.util.Set#iterator()
228:                 */
229:                public Iterator iterator() {
230:
231:                    return new Iterator() {
232:                        private Iterator it = entrySet.iterator();
233:
234:                        private Entry next = null;
235:
236:                        private Object value = null;
237:
238:                        /*
239:                         * Strong reference to key, so that the GC will leave it alone
240:                         * as long as this Entry exists
241:                         */
242:
243:                        public boolean hasNext() {
244:                            while (it.hasNext()) {
245:                                final Entry e = (Entry) it.next();
246:                                SoftEntry se = (SoftEntry) e.getValue();
247:                                value = null;
248:                                if ((se != null)
249:                                        && ((value = se.get()) == null)) {
250:                                    /* Weak key has been cleared by GC */
251:                                    continue;
252:                                }
253:                                next = new Map.Entry() {
254:                                    public Object getKey() {
255:                                        return e.getKey();
256:                                    }
257:
258:                                    public Object getValue() {
259:                                        return value;
260:                                    }
261:
262:                                    public Object setValue(final Object v) {
263:                                        Object res = value;
264:                                        value = v;
265:                                        e.setValue(new SoftEntry(e.getKey(),
266:                                                value, q));
267:                                        return res;
268:                                    }
269:
270:                                    public boolean equals(final Object x) {
271:                                        if (!(x instanceof  Map.Entry)) {
272:                                            return false;
273:                                        }
274:                                        Map.Entry e = (Map.Entry) x;
275:                                        Object key = getKey();
276:                                        return key == null ? e.getKey() == null
277:                                                : key.equals(e.getKey())
278:                                                        && value == null ? e
279:                                                        .getValue() == null
280:                                                        : value.equals(e
281:                                                                .getValue());
282:                                    }
283:
284:                                    public int hashCode() {
285:                                        Object key = getKey();
286:                                        return (((key == null) ? 0 : key
287:                                                .hashCode()) ^ ((value == null) ? 0
288:                                                : value.hashCode()));
289:                                    }
290:
291:                                };
292:                                return true;
293:                            }
294:                            return false;
295:                        }
296:
297:                        public Object next() {
298:                            if ((next == null) && !hasNext()) {
299:                                throw new NoSuchElementException();
300:                            }
301:                            Entry e = next;
302:                            next = null;
303:                            return e;
304:                        }
305:
306:                        public void remove() {
307:                            it.remove();
308:                        }
309:
310:                    };
311:                }
312:            }
313:        }
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