    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.collections4.collection;
    018
    019import java.io.Serializable;
    020import java.util.Collection;
    021import java.util.Iterator;
    022
    023/**
    024 * Decorates another <code>Collection</code> to provide additional behaviour.
    025 * <p>
    026 * Each method call made on this <code>Collection</code> is forwarded to the
    027 * decorated <code>Collection</code>. This class is used as a framework on which
    028 * to build to extensions such as synchronized and unmodifiable behaviour. The
    029 * main advantage of decoration is that one decorator can wrap any implementation
    030 * of <code>Collection</code>, whereas sub-classing requires a new class to be
    031 * written for each implementation.
    032 * <p>
    033 * This implementation does not perform any special processing with
    034 * {@link #iterator()}. Instead it simply returns the value from the
    035 * wrapped collection. This may be undesirable, for example if you are trying
    036 * to write an unmodifiable implementation it might provide a loophole.
    037 * <p>
    038 * This implementation does not forward the hashCode and equals methods through
    039 * to the backing object, but relies on Object's implementation. This is necessary
    040 * to preserve the symmetry of equals. Custom definitions of equality are usually
    041 * based on an interface, such as Set or List, so that the implementation of equals
    042 * can cast the object being tested for equality to the custom interface.
    043 * AbstractCollectionDecorator does not implement such custom interfaces directly;
    044 * they are implemented only in subclasses. Therefore, forwarding equals would break
    045 * symmetry, as the forwarding object might consider itself equal to the object being
    046 * tested, but the reverse could not be true. This behavior is consistent with the
    047 * JDK's collection wrappers, such as {@link java.util.Collections#unmodifiableCollection(Collection)}.
    048 * Use an interface-specific subclass of AbstractCollectionDecorator, such as
    049 * AbstractListDecorator, to preserve equality behavior, or override equals directly.
    050 *
    051 * @param <E> the type of the elements in the collection
    052 * @since 3.0
    053 */
    054public abstract class AbstractCollectionDecorator<E>
    055        implements Collection<E>, Serializable {
    056
    057    /** Serialization version */
    058    private static final long serialVersionUID = 6249888059822088500L;
    059
    060    /** The collection being decorated */
    061    private Collection<E> collection;
    062
    063    /**
    064     * Constructor only used in deserialization, do not use otherwise.
    065     * @since 3.1
    066     */
    067    protected AbstractCollectionDecorator() {
    068        super();
    069    }
    070
    071    /**
    072     * Constructor that wraps (not copies).
    073     *
    074     * @param coll  the collection to decorate, must not be null
    075     * @throws NullPointerException if the collection is null
    076     */
    077    protected AbstractCollectionDecorator(final Collection<E> coll) {
    078        if (coll == null) {
    079            throw new NullPointerException("Collection must not be null.");
    080        }
    081        this.collection = coll;
    082    }
    083
    084    /**
    085     * Gets the collection being decorated.
    086     * All access to the decorated collection goes via this method.
    087     *
    088     * @return the decorated collection
    089     */
    090    protected Collection<E> decorated() {
    091        return collection;
    092    }
    093
    094    /**
    095     * Sets the collection being decorated.
    096     * <p>
    097     * <b>NOTE:</b> this method should only be used during deserialization
    098     *
    099     * @param coll  the decorated collection
    100     */
    101    protected void setCollection(final Collection<E> coll) {
    102        this.collection = coll;
    103    }
    104
    105    //-----------------------------------------------------------------------
    106
    107    @Override
    108    public boolean add(final E object) {
    109        return decorated().add(object);
    110    }
    111
    112    @Override
    113    public boolean addAll(final Collection<? extends E> coll) {
    114        return decorated().addAll(coll);
    115    }
    116
    117    @Override
    118    public void clear() {
    119        decorated().clear();
    120    }
    121
    122    @Override
    123    public boolean contains(final Object object) {
    124        return decorated().contains(object);
    125    }
    126
    127    @Override
    128    public boolean isEmpty() {
    129        return decorated().isEmpty();
    130    }
    131
    132    @Override
    133    public Iterator<E> iterator() {
    134        return decorated().iterator();
    135    }
    136
    137    @Override
    138    public boolean remove(final Object object) {
    139        return decorated().remove(object);
    140    }
    141
    142    @Override
    143    public int size() {
    144        return decorated().size();
    145    }
    146
    147    @Override
    148    public Object[] toArray() {
    149        return decorated().toArray();
    150    }
    151
    152    @Override
    153    public <T> T[] toArray(final T[] object) {
    154        return decorated().toArray(object);
    155    }
    156
    157    @Override
    158    public boolean containsAll(final Collection<?> coll) {
    159        return decorated().containsAll(coll);
    160    }
    161
    162    @Override
    163    public boolean removeAll(final Collection<?> coll) {
    164        return decorated().removeAll(coll);
    165    }
    166
    167    @Override
    168    public boolean retainAll(final Collection<?> coll) {
    169        return decorated().retainAll(coll);
    170    }
    171
    172    @Override
    173    public String toString() {
    174        return decorated().toString();
    175    }
    176
    177}