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

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Here is the source code for de.dhke.projects.cutil.collections.cow.CopyOnWriteMultiMapValueCollection.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 org.apache.commons.collections15.MultiMap;

/**
 *
 * @param <K>
 * @param <V>
 * @param <M>
 * <p/>
 * @author Peter Wullinger <java@dhke.de>
 */
public class CopyOnWriteMultiMapValueCollection<K, V> implements Collection<V> {
    /// </editor-fold>
    private final CopyOnWriteMultiMap<K, V> _cowMap;
    private final Object _key;
    private MultiMap<K, V> _lastBaseMap = null;
    private Collection<V> _cachedValueCollection = null;

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

    protected CopyOnWriteMultiMapValueCollection(final CopyOnWriteMultiMap<K, V> cowMap, final Object key) {
        _key = key;
        _cowMap = cowMap;
    }

    @Override
    public int size() {
        if (_key == null)
            return getOriginalValueCollection().size();
        else
            return _cowMap.size(_key);
    }

    @Override
    public boolean isEmpty() {
        if (_key == null)
            return getOriginalValueCollection().isEmpty();
        else
            return (!_cowMap.containsKey(_key)) || (_cowMap.getDecoratee().get(_key).isEmpty());
    }

    @Override
    public boolean contains(final Object o) {
        if (_key == null)
            return _cowMap.containsValue(o);
        else
            return _cowMap.containsValue(_key, o);
    }

    @Override
    public Iterator<V> iterator() {
        if (_key == null)
            return new Itr();
        else
            return new Itr(_key);
    }

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

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

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

    @Override
    public boolean remove(final Object o) {
        _cowMap.copy();
        return getOriginalValueCollection().remove(o);
    }

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

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

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

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

    @Override
    public void clear() {
        getOriginalValueCollection().clear();
    }

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

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

    @Override
    public String toString() {
        return getOriginalValueCollection().toString();
    }

    private Collection<V> getOriginalValueCollection() {
        /* cache value set to avoid re-fetch */
        if (_lastBaseMap != _cowMap.getDecoratee()) {
            _lastBaseMap = _cowMap.getDecoratee();
            if (_key == null)
                _cachedValueCollection = _lastBaseMap.values();
            else
                _cachedValueCollection = _lastBaseMap.get(_key);
        }
        assert _cachedValueCollection != null;
        return _cachedValueCollection;
    }
    /// <editor-fold defaultstate="collapsed" desc="class Itr">

    private class Itr implements Iterator<V> {

        private final Iterator<V> _valueIterator;
        private final boolean _collectionAlreadyCopied;

        Itr() {
            _collectionAlreadyCopied = _cowMap.isWasCopied();
            _valueIterator = _cowMap.getDecoratee().values().iterator();
        }

        Itr(final Object key) {
            _collectionAlreadyCopied = _cowMap.isWasCopied();
            _valueIterator = _cowMap.getDecoratee().iterator(key);
        }

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

        @Override
        public V next() {
            return _valueIterator.next();
        }

        @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 chang 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 (_collectionAlreadyCopied)
                _valueIterator.remove();
            else
                throw new UnsupportedOperationException(
                        "Cannot remove from untouched CopyOnWriteMap via iterator.");
        }
    }
}