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.ListIterator;
022import org.checkerframework.checker.nullness.qual.Nullable;
023
024/**
025 * A list iterator which forwards all its method calls to another list iterator. Subclasses should
026 * override one or more methods to modify the behavior of the backing iterator as desired per the <a
027 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
028 *
029 * <p><b>{@code default} method warning:</b> This class forwards calls to <i>only some</i> {@code
030 * default} methods. Specifically, it forwards calls only for methods that existed <a
031 * href="https://docs.oracle.com/javase/7/docs/api/java/util/ListIterator.html">before {@code
032 * default} methods were introduced</a>. For newer methods, like {@code forEachRemaining}, it
033 * inherits their default implementations. When those implementations invoke methods, they invoke
034 * methods on the {@code ForwardingListIterator}.
035 *
036 * @author Mike Bostock
037 * @since 2.0
038 */
039@GwtCompatible
040@ElementTypesAreNonnullByDefault
041public abstract class ForwardingListIterator<E extends @Nullable Object>
042    extends ForwardingIterator<E> implements ListIterator<E> {
043
044  /** Constructor for use by subclasses. */
045  protected ForwardingListIterator() {}
046
047  @Override
048  protected abstract ListIterator<E> delegate();
049
050  @Override
051  public void add(@ParametricNullness E element) {
052    delegate().add(element);
053  }
054
055  @Override
056  public boolean hasPrevious() {
057    return delegate().hasPrevious();
058  }
059
060  @Override
061  public int nextIndex() {
062    return delegate().nextIndex();
063  }
064
065  @CanIgnoreReturnValue
066  @Override
067  @ParametricNullness
068  public E previous() {
069    return delegate().previous();
070  }
071
072  @Override
073  public int previousIndex() {
074    return delegate().previousIndex();
075  }
076
077  @Override
078  public void set(@ParametricNullness E element) {
079    delegate().set(element);
080  }
081}