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1 package fschmidt.util.java;
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2
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3 import java.lang.ref.Reference;
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4 import java.lang.ref.ReferenceQueue;
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5 import java.lang.ref.WeakReference;
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6 import java.util.concurrent.ConcurrentMap;
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7 import java.util.concurrent.ConcurrentHashMap;
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8
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9
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10 public final class Interner<T> {
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11
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12 private static final class MyReference<T> extends WeakReference<T> {
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13 private final int hash;
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14
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15 MyReference(T t,ReferenceQueue<T> q) {
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16 super(t,q);
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17 hash = t.hashCode();
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18 }
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19
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20 public boolean equals(Object obj) {
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21 if( this==obj )
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22 return true;
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23 if( !(obj instanceof MyReference) )
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24 return false;
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25 MyReference ref = (MyReference)obj;
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26 T t = this.get();
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27 if( t==null )
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28 return false;
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29 return t.equals(ref.get());
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30 }
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31
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32 public int hashCode() {
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33 return hash;
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34 }
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35 }
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36
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37 private final ConcurrentMap<MyReference<T>,MyReference<T>> map = new ConcurrentHashMap<MyReference<T>,MyReference<T>>();
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38 private ReferenceQueue<T> queue = new ReferenceQueue<T>();
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39
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40 private void sweep() {
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41 while(true) {
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42 Reference<? extends T> ref = queue.poll();
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43 if( ref == null )
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44 return;
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45 map.remove(ref);
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46 }
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47 }
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48
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49 public T intern(T t) {
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50 MyReference<T> ref = new MyReference<T>(t,queue);
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51 while(true) {
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52 MyReference<T> ref2 = map.putIfAbsent(ref,ref);
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53 if( ref2 == null ) {
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54 sweep();
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55 return t;
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56 }
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57 T t2 = ref2.get();
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58 if( t2 != null ) {
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59 ref.clear();
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60 return t2;
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61 }
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62 }
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63 }
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64
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65 }
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