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}