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.GwtCompatible; 020import com.google.errorprone.annotations.CanIgnoreReturnValue; 021import java.util.Collection; 022import java.util.Iterator; 023import java.util.List; 024import java.util.ListIterator; 025import javax.annotation.CheckForNull; 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 054@ElementTypesAreNonnullByDefault 055public abstract class ForwardingList<E extends @Nullable Object> extends ForwardingCollection<E> 056 implements List<E> { 057 // TODO(lowasser): identify places where thread safety is actually lost 058 059 /** Constructor for use by subclasses. */ 060 protected ForwardingList() {} 061 062 @Override 063 protected abstract List<E> delegate(); 064 065 @Override 066 public void add(int index, @ParametricNullness E element) { 067 delegate().add(index, element); 068 } 069 070 @CanIgnoreReturnValue 071 @Override 072 public boolean addAll(int index, Collection<? extends E> elements) { 073 return delegate().addAll(index, elements); 074 } 075 076 @Override 077 @ParametricNullness 078 public E get(int index) { 079 return delegate().get(index); 080 } 081 082 @Override 083 public int indexOf(@CheckForNull Object element) { 084 return delegate().indexOf(element); 085 } 086 087 @Override 088 public int lastIndexOf(@CheckForNull Object element) { 089 return delegate().lastIndexOf(element); 090 } 091 092 @Override 093 public ListIterator<E> listIterator() { 094 return delegate().listIterator(); 095 } 096 097 @Override 098 public ListIterator<E> listIterator(int index) { 099 return delegate().listIterator(index); 100 } 101 102 @CanIgnoreReturnValue 103 @Override 104 @ParametricNullness 105 public E remove(int index) { 106 return delegate().remove(index); 107 } 108 109 @CanIgnoreReturnValue 110 @Override 111 @ParametricNullness 112 public E set(int index, @ParametricNullness E element) { 113 return delegate().set(index, element); 114 } 115 116 @Override 117 public List<E> subList(int fromIndex, int toIndex) { 118 return delegate().subList(fromIndex, toIndex); 119 } 120 121 @Override 122 public boolean equals(@CheckForNull Object object) { 123 return object == this || delegate().equals(object); 124 } 125 126 @Override 127 public int hashCode() { 128 return delegate().hashCode(); 129 } 130 131 /** 132 * A sensible default implementation of {@link #add(Object)}, in terms of {@link #add(int, 133 * Object)}. If you override {@link #add(int, Object)}, you may wish to override {@link 134 * #add(Object)} to forward to this implementation. 135 * 136 * @since 7.0 137 */ 138 protected boolean standardAdd(@ParametricNullness E element) { 139 add(size(), element); 140 return true; 141 } 142 143 /** 144 * A sensible default implementation of {@link #addAll(int, Collection)}, in terms of the {@code 145 * add} method of {@link #listIterator(int)}. If you override {@link #listIterator(int)}, you may 146 * wish to override {@link #addAll(int, Collection)} to forward to this implementation. 147 * 148 * @since 7.0 149 */ 150 protected boolean standardAddAll(int index, Iterable<? extends E> elements) { 151 return Lists.addAllImpl(this, index, elements); 152 } 153 154 /** 155 * A sensible default implementation of {@link #indexOf}, in terms of {@link #listIterator()}. If 156 * you override {@link #listIterator()}, you may wish to override {@link #indexOf} to forward to 157 * this implementation. 158 * 159 * @since 7.0 160 */ 161 protected int standardIndexOf(@CheckForNull Object element) { 162 return Lists.indexOfImpl(this, element); 163 } 164 165 /** 166 * A sensible default implementation of {@link #lastIndexOf}, in terms of {@link 167 * #listIterator(int)}. If you override {@link #listIterator(int)}, you may wish to override 168 * {@link #lastIndexOf} to forward to this implementation. 169 * 170 * @since 7.0 171 */ 172 protected int standardLastIndexOf(@CheckForNull Object element) { 173 return Lists.lastIndexOfImpl(this, element); 174 } 175 176 /** 177 * A sensible default implementation of {@link #iterator}, in terms of {@link #listIterator()}. If 178 * you override {@link #listIterator()}, you may wish to override {@link #iterator} to forward to 179 * this implementation. 180 * 181 * @since 7.0 182 */ 183 protected Iterator<E> standardIterator() { 184 return listIterator(); 185 } 186 187 /** 188 * A sensible default implementation of {@link #listIterator()}, in terms of {@link 189 * #listIterator(int)}. If you override {@link #listIterator(int)}, you may wish to override 190 * {@link #listIterator()} to forward to this implementation. 191 * 192 * @since 7.0 193 */ 194 protected ListIterator<E> standardListIterator() { 195 return listIterator(0); 196 } 197 198 /** 199 * A sensible default implementation of {@link #listIterator(int)}, in terms of {@link #size}, 200 * {@link #get(int)}, {@link #set(int, Object)}, {@link #add(int, Object)}, and {@link 201 * #remove(int)}. If you override any of these methods, you may wish to override {@link 202 * #listIterator(int)} to forward to this implementation. 203 * 204 * @since 7.0 205 */ 206 protected ListIterator<E> standardListIterator(int start) { 207 return Lists.listIteratorImpl(this, start); 208 } 209 210 /** 211 * A sensible default implementation of {@link #subList(int, int)}. If you override any other 212 * methods, you may wish to override {@link #subList(int, int)} to forward to this implementation. 213 * 214 * @since 7.0 215 */ 216 protected List<E> standardSubList(int fromIndex, int toIndex) { 217 return Lists.subListImpl(this, fromIndex, toIndex); 218 } 219 220 /** 221 * A sensible definition of {@link #equals(Object)} in terms of {@link #size} and {@link 222 * #iterator}. If you override either of those methods, you may wish to override {@link 223 * #equals(Object)} to forward to this implementation. 224 * 225 * @since 7.0 226 */ 227 protected boolean standardEquals(@CheckForNull Object object) { 228 return Lists.equalsImpl(this, object); 229 } 230 231 /** 232 * A sensible definition of {@link #hashCode} in terms of {@link #iterator}. If you override 233 * {@link #iterator}, you may wish to override {@link #hashCode} to forward to this 234 * implementation. 235 * 236 * @since 7.0 237 */ 238 protected int standardHashCode() { 239 return Lists.hashCodeImpl(this); 240 } 241}