de.dhke.projects.cutil.collections.cow.CopyOnWriteMultiMapKeySet.java Source code

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Here is the source code for de.dhke.projects.cutil.collections.cow.CopyOnWriteMultiMapKeySet.java

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/**
 * (c) 2009-2014 Peter Wullinger
 *
 * $Id$
 *
 * Use, modification and restribution of this file are covered by the
 * terms of the Artistic License 2.0.
 *
 * You should have received a copy of the license terms in a file named
 * "LICENSE" together with this software package.
 *
 * Disclaimer of Warranty: THE PACKAGE IS PROVIDED BY THE COPYRIGHT
 * HOLDER AND CONTRIBUTORS "AS IS' AND WITHOUT ANY EXPRESS OR IMPLIED
 * WARRANTIES. THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR
 * A PARTICULAR PURPOSE, OR NON-INFRINGEMENT ARE DISCLAIMED TO THE
 * EXTENT PERMITTED BY YOUR LOCAL LAW. UNLESS REQUIRED BY LAW, NO
 * COPYRIGHT HOLDER OR CONTRIBUTOR WILL BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING IN ANY WAY OUT
 * OF THE USE OF THE PACKAGE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
 * DAMAGE.
 **/
package de.dhke.projects.cutil.collections.cow;

import java.util.Collection;
import java.util.Iterator;
import java.util.Set;
import org.apache.commons.collections15.MultiMap;

/**
 * This class is almost literally the same as CopyOnWriteMapKeySet
 *
 **/
/**
 *
 * @author Peter Wullinger <java@dhke.de>
 */
class CopyOnWriteMultiMapKeySet<K, V> implements Set<K> {

    private CopyOnWriteMultiMap<K, V> _cowMap;
    private MultiMap<K, V> _lastBaseMap = null;
    private Set<K> _cachedKeySet = null;

    protected CopyOnWriteMultiMapKeySet(final CopyOnWriteMultiMap<K, V> cowMap) {
        _cowMap = cowMap;
    }

    @Override
    public int size() {
        return _cowMap.size();
    }

    @Override
    public boolean isEmpty() {
        return _cowMap.isEmpty();
    }

    @Override
    public boolean contains(final Object o) {
        return _cowMap.containsKey(o);
    }

    @Override
    public Iterator<K> iterator() {
        return new Itr();
    }

    @Override
    public Object[] toArray() {
        return getOriginalKeySet().toArray();
    }

    @Override
    public <T> T[] toArray(final T[] a) {
        return getOriginalKeySet().toArray(a);
    }

    @Override
    public boolean add(K key) {
        throw new UnsupportedOperationException("Cannot add to key set");
    }

    @Override
    public boolean remove(final Object o) {
        boolean willRemove = _cowMap.containsKey(o);
        _cowMap.remove(o);
        return willRemove;
    }

    @Override
    public boolean containsAll(final Collection<?> c) {
        return getOriginalKeySet().containsAll(c);
    }

    @Override
    public boolean addAll(final Collection<? extends K> c) {
        throw new UnsupportedOperationException("Cannot add to key set");
    }

    @Override
    public boolean retainAll(final Collection<?> c) {
        _cowMap.copy();
        return getOriginalKeySet().retainAll(c);
    }

    @Override
    public boolean removeAll(final Collection<?> c) {
        _cowMap.copy();
        return getOriginalKeySet().removeAll(c);
    }

    @Override
    public void clear() {
        _cowMap.copy();
        _cowMap.getDecoratee().clear();
    }

    @Override
    public boolean equals(final Object obj) {
        if (this == obj)
            return true;
        return getOriginalKeySet().equals(obj);
    }

    @Override
    public int hashCode() {
        int hCode = 0;
        for (K key : this)
            hCode += key.hashCode();
        return hCode;
    }

    private Set<K> getOriginalKeySet() {
        /* cache value set to avoid re-fetch */
        if (_lastBaseMap != _cowMap.getDecoratee()) {
            _lastBaseMap = _cowMap.getDecoratee();
            _cachedKeySet = _lastBaseMap.keySet();
        }
        assert _cachedKeySet != null;
        return _cachedKeySet;
    }

    /// <editor-fold defaultstate="collapsed" desc="class Itr">
    private class Itr implements Iterator<K> {
        private Iterator<K> _keyIterator;
        /**
         * the iteration position of this iterator.
         * 
         * if _iterPos == -2, we operate on an already copied COWmap and
         * simple iterate.
         * 
         * if _iterPos >= -1, we operate 
         */
        private int _iterPos;

        Itr() {
            if (_cowMap.isWasCopied()) {
                _iterPos = -2;
            } else
                _iterPos = -1;
            _keyIterator = _cowMap.getDecoratee().keySet().iterator();
        }

        @Override
        public boolean hasNext() {
            return _keyIterator.hasNext();
        }

        @Override
        public K next() {
            final K key = _keyIterator.next();
            if (_iterPos >= -1)
                ++_iterPos;
            return key;
        }

        @Override
        public void remove() {
            /**
             * I cannot think of a proper way to fully support this method.
             * If a COW list has not been copied yet, a remove would change thee underlying collection.
             * In this case, we would have to create a new iterator at exactly the same
             * position for the new collection. This works for lists but not for collections.
             **/
            if (_iterPos == -2)
                _keyIterator.remove();
            else {
                assert !_cowMap.isWasCopied();
                _cowMap.copy();
                assert _cowMap.isWasCopied();
                _keyIterator = _cowMap.getDecoratee().keySet().iterator();
                for (int i = -1; i < _iterPos; ++i)
                    _keyIterator.next();
                _iterPos = -2;
                _keyIterator.remove();
            }
        }
    }
    /// </editor-fold>
}