001/* 002 * Copyright (C) 2007 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * http://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package com.google.common.collect; 018 019import com.google.common.annotations.Beta; 020import com.google.common.annotations.GwtCompatible; 021import com.google.errorprone.annotations.CanIgnoreReturnValue; 022import java.util.Collection; 023import java.util.Iterator; 024import java.util.List; 025import java.util.ListIterator; 026import org.checkerframework.checker.nullness.qual.Nullable; 027 028/** 029 * A list which forwards all its method calls to another list. Subclasses should override one or 030 * more methods to modify the behavior of the backing list as desired per the <a 031 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>. 032 * 033 * <p>This class does not implement {@link java.util.RandomAccess}. If the delegate supports random 034 * access, the {@code ForwardingList} subclass should implement the {@code RandomAccess} interface. 035 * 036 * <p><b>Warning:</b> The methods of {@code ForwardingList} forward <b>indiscriminately</b> to the 037 * methods of the delegate. For example, overriding {@link #add} alone <b>will not</b> change the 038 * behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you should 039 * override {@code addAll} as well, either providing your own implementation, or delegating to the 040 * provided {@code standardAddAll} method. 041 * 042 * <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code 043 * default} methods. Instead, it inherits their default implementations. When those implementations 044 * invoke methods, they invoke methods on the {@code ForwardingList}. 045 * 046 * <p>The {@code standard} methods and any collection views they return are not guaranteed to be 047 * thread-safe, even when all of the methods that they depend on are thread-safe. 048 * 049 * @author Mike Bostock 050 * @author Louis Wasserman 051 * @since 2.0 052 */ 053@GwtCompatible 054public abstract class ForwardingList<E> extends ForwardingCollection<E> implements List<E> { 055 // TODO(lowasser): identify places where thread safety is actually lost 056 057 /** Constructor for use by subclasses. */ 058 protected ForwardingList() {} 059 060 @Override 061 protected abstract List<E> delegate(); 062 063 @Override 064 public void add(int index, E element) { 065 delegate().add(index, element); 066 } 067 068 @CanIgnoreReturnValue 069 @Override 070 public boolean addAll(int index, Collection<? extends E> elements) { 071 return delegate().addAll(index, elements); 072 } 073 074 @Override 075 public E get(int index) { 076 return delegate().get(index); 077 } 078 079 @Override 080 public int indexOf(Object element) { 081 return delegate().indexOf(element); 082 } 083 084 @Override 085 public int lastIndexOf(Object element) { 086 return delegate().lastIndexOf(element); 087 } 088 089 @Override 090 public ListIterator<E> listIterator() { 091 return delegate().listIterator(); 092 } 093 094 @Override 095 public ListIterator<E> listIterator(int index) { 096 return delegate().listIterator(index); 097 } 098 099 @CanIgnoreReturnValue 100 @Override 101 public E remove(int index) { 102 return delegate().remove(index); 103 } 104 105 @CanIgnoreReturnValue 106 @Override 107 public E set(int index, E element) { 108 return delegate().set(index, element); 109 } 110 111 @Override 112 public List<E> subList(int fromIndex, int toIndex) { 113 return delegate().subList(fromIndex, toIndex); 114 } 115 116 @Override 117 public boolean equals(@Nullable Object object) { 118 return object == this || delegate().equals(object); 119 } 120 121 @Override 122 public int hashCode() { 123 return delegate().hashCode(); 124 } 125 126 /** 127 * A sensible default implementation of {@link #add(Object)}, in terms of {@link #add(int, 128 * Object)}. If you override {@link #add(int, Object)}, you may wish to override {@link 129 * #add(Object)} to forward to this implementation. 130 * 131 * @since 7.0 132 */ 133 protected boolean standardAdd(E element) { 134 add(size(), element); 135 return true; 136 } 137 138 /** 139 * A sensible default implementation of {@link #addAll(int, Collection)}, in terms of the {@code 140 * add} method of {@link #listIterator(int)}. If you override {@link #listIterator(int)}, you may 141 * wish to override {@link #addAll(int, Collection)} to forward to this implementation. 142 * 143 * @since 7.0 144 */ 145 protected boolean standardAddAll(int index, Iterable<? extends E> elements) { 146 return Lists.addAllImpl(this, index, elements); 147 } 148 149 /** 150 * A sensible default implementation of {@link #indexOf}, in terms of {@link #listIterator()}. If 151 * you override {@link #listIterator()}, you may wish to override {@link #indexOf} to forward to 152 * this implementation. 153 * 154 * @since 7.0 155 */ 156 protected int standardIndexOf(@Nullable Object element) { 157 return Lists.indexOfImpl(this, element); 158 } 159 160 /** 161 * A sensible default implementation of {@link #lastIndexOf}, in terms of {@link 162 * #listIterator(int)}. If you override {@link #listIterator(int)}, you may wish to override 163 * {@link #lastIndexOf} to forward to this implementation. 164 * 165 * @since 7.0 166 */ 167 protected int standardLastIndexOf(@Nullable Object element) { 168 return Lists.lastIndexOfImpl(this, element); 169 } 170 171 /** 172 * A sensible default implementation of {@link #iterator}, in terms of {@link #listIterator()}. If 173 * you override {@link #listIterator()}, you may wish to override {@link #iterator} to forward to 174 * this implementation. 175 * 176 * @since 7.0 177 */ 178 protected Iterator<E> standardIterator() { 179 return listIterator(); 180 } 181 182 /** 183 * A sensible default implementation of {@link #listIterator()}, in terms of {@link 184 * #listIterator(int)}. If you override {@link #listIterator(int)}, you may wish to override 185 * {@link #listIterator()} to forward to this implementation. 186 * 187 * @since 7.0 188 */ 189 protected ListIterator<E> standardListIterator() { 190 return listIterator(0); 191 } 192 193 /** 194 * A sensible default implementation of {@link #listIterator(int)}, in terms of {@link #size}, 195 * {@link #get(int)}, {@link #set(int, Object)}, {@link #add(int, Object)}, and {@link 196 * #remove(int)}. If you override any of these methods, you may wish to override {@link 197 * #listIterator(int)} to forward to this implementation. 198 * 199 * @since 7.0 200 */ 201 @Beta 202 protected ListIterator<E> standardListIterator(int start) { 203 return Lists.listIteratorImpl(this, start); 204 } 205 206 /** 207 * A sensible default implementation of {@link #subList(int, int)}. If you override any other 208 * methods, you may wish to override {@link #subList(int, int)} to forward to this implementation. 209 * 210 * @since 7.0 211 */ 212 @Beta 213 protected List<E> standardSubList(int fromIndex, int toIndex) { 214 return Lists.subListImpl(this, fromIndex, toIndex); 215 } 216 217 /** 218 * A sensible definition of {@link #equals(Object)} in terms of {@link #size} and {@link 219 * #iterator}. If you override either of those methods, you may wish to override {@link 220 * #equals(Object)} to forward to this implementation. 221 * 222 * @since 7.0 223 */ 224 @Beta 225 protected boolean standardEquals(@Nullable Object object) { 226 return Lists.equalsImpl(this, object); 227 } 228 229 /** 230 * A sensible definition of {@link #hashCode} in terms of {@link #iterator}. If you override 231 * {@link #iterator}, you may wish to override {@link #hashCode} to forward to this 232 * implementation. 233 * 234 * @since 7.0 235 */ 236 @Beta 237 protected int standardHashCode() { 238 return Lists.hashCodeImpl(this); 239 } 240}