path: root/guava/src/com/google/common/collect/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.GwtCompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import javax.annotation.CheckForNull;
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
@ElementTypesAreNonnullByDefault
public abstract class ForwardingList<E extends @Nullable Object> 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, @ParametricNullness E element) {
    delegate().add(index, element);
  }

  @CanIgnoreReturnValue
  @Override
  public boolean addAll(int index, Collection<? extends E> elements) {
    return delegate().addAll(index, elements);
  }

  @Override
  @ParametricNullness
  public E get(int index) {
    return delegate().get(index);
  }

  @Override
  public int indexOf(@CheckForNull Object element) {
    return delegate().indexOf(element);
  }

  @Override
  public int lastIndexOf(@CheckForNull 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
  @ParametricNullness
  public E remove(int index) {
    return delegate().remove(index);
  }

  @CanIgnoreReturnValue
  @Override
  @ParametricNullness
  public E set(int index, @ParametricNullness 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(@CheckForNull 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(@ParametricNullness 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(@CheckForNull 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(@CheckForNull 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
   */
  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
   */
  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
   */
  protected boolean standardEquals(@CheckForNull 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
   */
  protected int standardHashCode() {
    return Lists.hashCodeImpl(this);
  }
}