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1 package goodjava.util;
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2
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3 import java.lang.ref.ReferenceQueue;
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4 import java.util.Map;
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5 import java.util.AbstractMap;
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6 import java.util.HashMap;
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7 import java.util.Set;
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8 import java.util.AbstractSet;
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9 import java.util.Iterator;
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10
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11
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12 public abstract class CacheMap<K,V> extends AbstractMap<K,V> {
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13
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14 protected static interface MyReference<K,V> {
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15 public K key();
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16 public V get();
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17 public void clear();
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18 }
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19
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20 protected abstract MyReference<K,V> newReference(K key,V value,ReferenceQueue<V> q);
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21
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22 private final Map<K,MyReference<K,V>> cache = new HashMap<K,MyReference<K,V>>();
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23 private final ReferenceQueue<V> queue = new ReferenceQueue<V>();
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24
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25 private void sweep() {
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26 while(true) {
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27 @SuppressWarnings("unchecked")
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28 MyReference<K,V> ref = (MyReference<K,V>)queue.poll();
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29 if( ref == null )
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30 return;
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31 MyReference<K,V> mappedRef = cache.remove(ref.key());
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32 if( mappedRef != ref && mappedRef != null )
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33 cache.put( mappedRef.key(), mappedRef ); // put it back
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34 }
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35 }
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36
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1607
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37 @Override public int size() {
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38 return cache.size();
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39 }
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40
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1607
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41 @Override public boolean isEmpty() {
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42 return cache.isEmpty();
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43 }
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44
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45 @Override public boolean containsKey(Object key) {
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46 return cache.containsKey(key);
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47 }
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48
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49 @Override public V get(Object key) {
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50 MyReference<K,V> ref = cache.get(key);
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51 return ref==null ? null : ref.get();
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52 }
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53
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54 @Override public V put(K key,V value) {
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55 sweep();
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56 MyReference<K,V> ref = cache.put( key, newReference(key,value,queue) );
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57 return ref==null ? null : ref.get();
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58 }
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59
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1607
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60 @Override public V remove(Object key) {
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61 sweep();
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62 MyReference<K,V> ref = cache.remove(key);
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63 return ref==null ? null : ref.get();
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64 }
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65
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66 @Override public void clear() {
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67 sweep();
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68 cache.clear();
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69 }
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70
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71 /*
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72 public Object clone() {
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73 GCCacheMap map = new GCCacheMap();
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74 map.cache = (HashMap)cache.clone();
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75 return map;
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76 }
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77 */
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78 @Override public Set<K> keySet() {
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79 return cache.keySet();
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80 }
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81
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82 @Override public Set<Map.Entry<K,V>> entrySet() {
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83 return new MySet();
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84 }
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85
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86
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87 private class MySet extends AbstractSet<Map.Entry<K,V>> {
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88
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89 @Override public int size() {
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90 return CacheMap.this.size();
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91 }
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92
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93 @Override public Iterator<Map.Entry<K,V>> iterator() {
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94 return new MyIterator();
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95 }
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96
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97 }
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98
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99 private class MyIterator implements Iterator<Map.Entry<K,V>> {
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100 final Iterator<Map.Entry<K,MyReference<K,V>>> iter = cache.entrySet().iterator();
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101
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102 @Override public boolean hasNext() {
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103 return iter.hasNext();
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104 }
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105
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106 @Override public void remove() {
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107 iter.remove();
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108 }
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109
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110 @Override public Map.Entry<K,V> next() {
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111 return new MyEntry( iter.next() );
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112 }
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113 }
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114
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115 private class MyEntry implements Map.Entry<K,V> {
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116 Map.Entry<K,MyReference<K,V>> entry;
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117
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118 MyEntry(Map.Entry<K,MyReference<K,V>> entry) {
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119 this.entry = entry;
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120 }
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121
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122 @Override public K getKey() {
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123 return entry.getKey();
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124 }
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125
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126 @Override public V getValue() {
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127 MyReference<K,V> ref = entry.getValue();
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128 return ref.get();
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129 }
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130
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131 @Override public V setValue(V value) {
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132 MyReference<K,V> ref = entry.setValue( newReference(getKey(),value,queue) );
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133 return ref.get();
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134 }
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135
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136 @Override public boolean equals(Object o) {
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137 if( o==null || !(o instanceof CacheMap.MyEntry) )
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138 return false;
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139 @SuppressWarnings("unchecked")
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140 MyEntry m = (MyEntry)o;
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141 return entry.equals(m.entry);
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142 }
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143
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144 @Override public int hashCode() {
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145 K key = getKey();
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146 V value = getValue();
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147 return (key==null ? 0 : key.hashCode()) ^
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148 (value==null ? 0 : value.hashCode());
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149 }
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150 }
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151
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152 }
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