    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;
    022import java.util.function.Predicate;
    023
    024/**
    025 * Decorates another <code>Collection</code> to provide additional behaviour.
    026 * <p>
    027 * Each method call made on this <code>Collection</code> is forwarded to the
    028 * decorated <code>Collection</code>. This class is used as a framework on which
    029 * to build to extensions such as synchronized and unmodifiable behaviour. The
    030 * main advantage of decoration is that one decorator can wrap any implementation
    031 * of <code>Collection</code>, whereas sub-classing requires a new class to be
    032 * written for each implementation.
    033 * </p>
    034 * <p>
    035 * This implementation does not perform any special processing with
    036 * {@link #iterator()}. Instead it simply returns the value from the
    037 * wrapped collection. This may be undesirable, for example if you are trying
    038 * to write an unmodifiable implementation it might provide a loophole.
    039 * </p>
    040 * <p>
    041 * This implementation does not forward the hashCode and equals methods through
    042 * to the backing object, but relies on Object's implementation. This is necessary
    043 * to preserve the symmetry of equals. Custom definitions of equality are usually
    044 * based on an interface, such as Set or List, so that the implementation of equals
    045 * can cast the object being tested for equality to the custom interface.
    046 * AbstractCollectionDecorator does not implement such custom interfaces directly;
    047 * they are implemented only in subclasses. Therefore, forwarding equals would break
    048 * symmetry, as the forwarding object might consider itself equal to the object being
    049 * tested, but the reverse could not be true. This behavior is consistent with the
    050 * JDK's collection wrappers, such as {@link java.util.Collections#unmodifiableCollection(Collection)}.
    051 * Use an interface-specific subclass of AbstractCollectionDecorator, such as
    052 * AbstractListDecorator, to preserve equality behavior, or override equals directly.
    053 * </p>
    054 *
    055 * @param <E> the type of the elements in the collection
    056 * @since 3.0
    057 */
    058public abstract class AbstractCollectionDecorator<E>
    059        implements Collection<E>, Serializable {
    060
    061    /** Serialization version */
    062    private static final long serialVersionUID = 6249888059822088500L;
    063
    064    /** The collection being decorated */
    065    private Collection<E> collection;
    066
    067    /**
    068     * Constructor only used in deserialization, do not use otherwise.
    069     * @since 3.1
    070     */
    071    protected AbstractCollectionDecorator() {
    072        super();
    073    }
    074
    075    /**
    076     * Constructor that wraps (not copies).
    077     *
    078     * @param coll  the collection to decorate, must not be null
    079     * @throws NullPointerException if the collection is null
    080     */
    081    protected AbstractCollectionDecorator(final Collection<E> coll) {
    082        if (coll == null) {
    083            throw new NullPointerException("Collection must not be null.");
    084        }
    085        this.collection = coll;
    086    }
    087
    088    /**
    089     * Gets the collection being decorated.
    090     * All access to the decorated collection goes via this method.
    091     *
    092     * @return the decorated collection
    093     */
    094    protected Collection<E> decorated() {
    095        return collection;
    096    }
    097
    098    /**
    099     * Sets the collection being decorated.
    100     * <p>
    101     * <b>NOTE:</b> this method should only be used during deserialization
    102     *
    103     * @param coll  the decorated collection
    104     */
    105    protected void setCollection(final Collection<E> coll) {
    106        this.collection = coll;
    107    }
    108
    109    //-----------------------------------------------------------------------
    110
    111    @Override
    112    public boolean add(final E object) {
    113        return decorated().add(object);
    114    }
    115
    116    @Override
    117    public boolean addAll(final Collection<? extends E> coll) {
    118        return decorated().addAll(coll);
    119    }
    120
    121    @Override
    122    public void clear() {
    123        decorated().clear();
    124    }
    125
    126    @Override
    127    public boolean contains(final Object object) {
    128        return decorated().contains(object);
    129    }
    130
    131    @Override
    132    public boolean isEmpty() {
    133        return decorated().isEmpty();
    134    }
    135
    136    @Override
    137    public Iterator<E> iterator() {
    138        return decorated().iterator();
    139    }
    140
    141    @Override
    142    public boolean remove(final Object object) {
    143        return decorated().remove(object);
    144    }
    145
    146    @Override
    147    public int size() {
    148        return decorated().size();
    149    }
    150
    151    @Override
    152    public Object[] toArray() {
    153        return decorated().toArray();
    154    }
    155
    156    @Override
    157    public <T> T[] toArray(final T[] object) {
    158        return decorated().toArray(object);
    159    }
    160
    161    @Override
    162    public boolean containsAll(final Collection<?> coll) {
    163        return decorated().containsAll(coll);
    164    }
    165
    166    /**
    167     * @since 4.4
    168     */
    169    @Override
    170    public boolean removeIf(final Predicate<? super E> filter) {
    171        return decorated().removeIf(filter);
    172    }
    173
    174    @Override
    175    public boolean removeAll(final Collection<?> coll) {
    176        return decorated().removeAll(coll);
    177    }
    178
    179    @Override
    180    public boolean retainAll(final Collection<?> coll) {
    181        return decorated().retainAll(coll);
    182    }
    183
    184    @Override
    185    public String toString() {
    186        return decorated().toString();
    187    }
    188
    189}