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