ForwardingList.java
/*
* Copyright (C) 2007 The Guava Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.common.collect;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* A list which forwards all its method calls to another list. Subclasses should override one or
* more methods to modify the behavior of the backing list as desired per the <a
* href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
*
* <p>This class does not implement {@link java.util.RandomAccess}. If the delegate supports random
* access, the {@code ForwardingList} subclass should implement the {@code RandomAccess} interface.
*
* <p><b>Warning:</b> The methods of {@code ForwardingList} forward <b>indiscriminately</b> to the
* methods of the delegate. For example, overriding {@link #add} alone <b>will not</b> change the
* behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you should
* override {@code addAll} as well, either providing your own implementation, or delegating to the
* provided {@code standardAddAll} method.
*
* <p><b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
* default} methods. Instead, it inherits their default implementations. When those implementations
* invoke methods, they invoke methods on the {@code ForwardingList}.
*
* <p>The {@code standard} methods and any collection views they return are not guaranteed to be
* thread-safe, even when all of the methods that they depend on are thread-safe.
*
* @author Mike Bostock
* @author Louis Wasserman
* @since 2.0
*/
@GwtCompatible
public abstract class ForwardingList<E> extends ForwardingCollection<E> implements List<E> {
// TODO(lowasser): identify places where thread safety is actually lost
/** Constructor for use by subclasses. */
protected ForwardingList() {}
@Override
protected abstract List<E> delegate();
@Override
public void add(int index, E element) {
delegate().add(index, element);
}
@CanIgnoreReturnValue
@Override
public boolean addAll(int index, Collection<? extends E> elements) {
return delegate().addAll(index, elements);
}
@Override
public E get(int index) {
return delegate().get(index);
}
@Override
public int indexOf(Object element) {
return delegate().indexOf(element);
}
@Override
public int lastIndexOf(Object element) {
return delegate().lastIndexOf(element);
}
@Override
public ListIterator<E> listIterator() {
return delegate().listIterator();
}
@Override
public ListIterator<E> listIterator(int index) {
return delegate().listIterator(index);
}
@CanIgnoreReturnValue
@Override
public E remove(int index) {
return delegate().remove(index);
}
@CanIgnoreReturnValue
@Override
public E set(int index, E element) {
return delegate().set(index, element);
}
@Override
public List<E> subList(int fromIndex, int toIndex) {
return delegate().subList(fromIndex, toIndex);
}
@Override
public boolean equals(@Nullable Object object) {
return object == this || delegate().equals(object);
}
@Override
public int hashCode() {
return delegate().hashCode();
}
/**
* A sensible default implementation of {@link #add(Object)}, in terms of {@link #add(int,
* Object)}. If you override {@link #add(int, Object)}, you may wish to override {@link
* #add(Object)} to forward to this implementation.
*
* @since 7.0
*/
protected boolean standardAdd(E element) {
add(size(), element);
return true;
}
/**
* A sensible default implementation of {@link #addAll(int, Collection)}, in terms of the {@code
* add} method of {@link #listIterator(int)}. If you override {@link #listIterator(int)}, you may
* wish to override {@link #addAll(int, Collection)} to forward to this implementation.
*
* @since 7.0
*/
protected boolean standardAddAll(int index, Iterable<? extends E> elements) {
return Lists.addAllImpl(this, index, elements);
}
/**
* A sensible default implementation of {@link #indexOf}, in terms of {@link #listIterator()}. If
* you override {@link #listIterator()}, you may wish to override {@link #indexOf} to forward to
* this implementation.
*
* @since 7.0
*/
protected int standardIndexOf(@Nullable Object element) {
return Lists.indexOfImpl(this, element);
}
/**
* A sensible default implementation of {@link #lastIndexOf}, in terms of {@link
* #listIterator(int)}. If you override {@link #listIterator(int)}, you may wish to override
* {@link #lastIndexOf} to forward to this implementation.
*
* @since 7.0
*/
protected int standardLastIndexOf(@Nullable Object element) {
return Lists.lastIndexOfImpl(this, element);
}
/**
* A sensible default implementation of {@link #iterator}, in terms of {@link #listIterator()}. If
* you override {@link #listIterator()}, you may wish to override {@link #iterator} to forward to
* this implementation.
*
* @since 7.0
*/
protected Iterator<E> standardIterator() {
return listIterator();
}
/**
* A sensible default implementation of {@link #listIterator()}, in terms of {@link
* #listIterator(int)}. If you override {@link #listIterator(int)}, you may wish to override
* {@link #listIterator()} to forward to this implementation.
*
* @since 7.0
*/
protected ListIterator<E> standardListIterator() {
return listIterator(0);
}
/**
* A sensible default implementation of {@link #listIterator(int)}, in terms of {@link #size},
* {@link #get(int)}, {@link #set(int, Object)}, {@link #add(int, Object)}, and {@link
* #remove(int)}. If you override any of these methods, you may wish to override {@link
* #listIterator(int)} to forward to this implementation.
*
* @since 7.0
*/
@Beta
protected ListIterator<E> standardListIterator(int start) {
return Lists.listIteratorImpl(this, start);
}
/**
* A sensible default implementation of {@link #subList(int, int)}. If you override any other
* methods, you may wish to override {@link #subList(int, int)} to forward to this implementation.
*
* @since 7.0
*/
@Beta
protected List<E> standardSubList(int fromIndex, int toIndex) {
return Lists.subListImpl(this, fromIndex, toIndex);
}
/**
* A sensible definition of {@link #equals(Object)} in terms of {@link #size} and {@link
* #iterator}. If you override either of those methods, you may wish to override {@link
* #equals(Object)} to forward to this implementation.
*
* @since 7.0
*/
@Beta
protected boolean standardEquals(@Nullable Object object) {
return Lists.equalsImpl(this, object);
}
/**
* A sensible definition of {@link #hashCode} in terms of {@link #iterator}. If you override
* {@link #iterator}, you may wish to override {@link #hashCode} to forward to this
* implementation.
*
* @since 7.0
*/
@Beta
protected int standardHashCode() {
return Lists.hashCodeImpl(this);
}
}