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}