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.Iterator;
022import org.checkerframework.checker.nullness.qual.Nullable;
023
024/**
025 * An iterator which forwards all its method calls to another iterator. Subclasses should override
026 * 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/Iterator.html">before {@code default}
032 * methods were introduced</a>. For newer methods, like {@code forEachRemaining}, it inherits their
033 * default implementations. When those implementations invoke methods, they invoke methods on the
034 * {@code ForwardingIterator}.
035 *
036 * @author Kevin Bourrillion
037 * @since 2.0
038 */
039@GwtCompatible
040@ElementTypesAreNonnullByDefault
041public abstract class ForwardingIterator<T extends @Nullable Object> extends ForwardingObject
042    implements Iterator<T> {
043
044  /** Constructor for use by subclasses. */
045  protected ForwardingIterator() {}
046
047  @Override
048  protected abstract Iterator<T> delegate();
049
050  @Override
051  public boolean hasNext() {
052    return delegate().hasNext();
053  }
054
055  @CanIgnoreReturnValue
056  @Override
057  @ParametricNullness
058  public T next() {
059    return delegate().next();
060  }
061
062  @Override
063  public void remove() {
064    delegate().remove();
065  }
066}