001    /*
002     *  This file is part of the Jikes RVM project (http://jikesrvm.org).
003     *
004     *  This file is licensed to You under the Eclipse Public License (EPL);
005     *  You may not use this file except in compliance with the License. You
006     *  may obtain a copy of the License at
007     *
008     *      http://www.opensource.org/licenses/eclipse-1.0.php
009     *
010     *  See the COPYRIGHT.txt file distributed with this work for information
011     *  regarding copyright ownership.
012     */
013    package org.jikesrvm.util;
014    
015    import org.jikesrvm.util.ImmutableEntryHashMapRVM.Bucket;
016    import org.jikesrvm.runtime.Magic;
017    
018    /**
019     * A hash map with entirely immutable buckets. It doesn't correctly support
020     * remove, and its values cannot be mutated by a put with the same key.
021     */
022    public final class ImmutableEntryIdentityHashMapRVM<K, V> extends AbstractHashMapRVM<K,V> {
023    
024      @Override
025      AbstractBucket<K,V> createNewBucket(K key, V value, AbstractBucket<K, V> next) {
026        return new Bucket<K,V>(key, value, next);
027      }
028    
029      public ImmutableEntryIdentityHashMapRVM() {
030        super(DEFAULT_SIZE);
031      }
032    
033      public ImmutableEntryIdentityHashMapRVM(int size) {
034        super(size);
035      }
036    
037      @Override
038      protected boolean same(K k1, K k2) {
039        return k1 == k2;
040      }
041    
042      @Override
043      protected int hashTheKey(K key) {
044        if (!org.jikesrvm.VM.runningVM) {
045          return Magic.bootImageIdentityHashCode(key);
046        } else {
047          return System.identityHashCode(key);
048        }
049      }
050    }