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    /**
016     * A hash set with entirely immutable buckets. It doesn't correctly support
017     * remove, so use with care.
018     */
019    public final class ImmutableEntryHashSetRVM<T> extends AbstractHashSetRVM<T> {
020    
021      static final class Bucket<T> extends AbstractBucket<T> {
022        private final T key;
023        private final AbstractBucket<T> next;
024    
025        Bucket(T key, AbstractBucket<T> next) {
026          this.key = key;
027          this.next = next;
028        }
029    
030        @Override
031        AbstractBucket<T> setNext(AbstractBucket<T> next) {
032          if (this.next == next) {
033            return this;
034          } else {
035            return new Bucket<T>(key, next);
036          }
037        }
038    
039        @Override
040        AbstractBucket<T> getNext() {
041          return next;
042        }
043    
044        @Override
045        T getKey() {
046          return key;
047        }
048      }
049    
050      @Override
051      AbstractBucket<T> createNewBucket(T key, AbstractBucket<T> next) {
052        return new Bucket<T>(key, next);
053      }
054    
055      public ImmutableEntryHashSetRVM() {
056        super(DEFAULT_SIZE);
057      }
058    
059      public ImmutableEntryHashSetRVM(int size) {
060        super(size);
061      }
062    
063      @Override
064      public void remove(T key) {
065        throw new UnsupportedOperationException();
066      }
067    }