*
 * <p>The Guava User Guide has <a
 * href="https://github.com/google/guava/wiki/GraphsExplained#building-graph-instances">more
 * information on (and examples of) building graphs</a>.
 *
 * <h3>Additional documentation</h3>
 *
 * <p>See the Guava User Guide for the {@code common.graph} package (<a
 * href="https://github.com/google/guava/wiki/GraphsExplained">"Graphs Explained"</a>) for

 *
 * <p>The Guava User Guide has <a
 * href="https://github.com/google/guava/wiki/GraphsExplained#building-graph-instances">more
 * information on (and examples of) building graphs</a>.
 *
 * <h3>Additional documentation</h3>
 *
 * <p>See the Guava User Guide for the {@code common.graph} package (<a
 * href="https://github.com/google/guava/wiki/GraphsExplained">"Graphs Explained"</a>) for

 *       where the {@code ...} contains the names of all the other {@code ParametricNullness}
 *       annotations in Guava. Or you might prefer to omit Guava from your {@code AnnotatedPackages}
 *       list.
 *   <li><a href="https://developers.google.com/j2objc">J2ObjC</a>
 *   <li>{@code NullPointerTester}, at least in the Android backport (where the type-use annotations

 *       where the {@code ...} contains the names of all the other {@code ParametricNullness}
 *       annotations in Guava. Or you might prefer to omit Guava from your {@code AnnotatedPackages}
 *       list.
 *   <li><a href="https://developers.google.com/j2objc">J2ObjC</a>
 *   <li>{@code NullPointerTester}, at least in the Android backport (where the type-use annotations

 *       where the {@code ...} contains the names of all the other {@code ParametricNullness}
 *       annotations in Guava. Or you might prefer to omit Guava from your {@code AnnotatedPackages}
 *       list.
 *   <li><a href="https://developers.google.com/j2objc">J2ObjC</a>
 *   <li>{@code NullPointerTester}, at least in the Android backport (where the type-use annotations

 *       where the {@code ...} contains the names of all the other {@code ParametricNullness}
 *       annotations in Guava. Or you might prefer to omit Guava from your {@code AnnotatedPackages}
 *       list.
 *   <li><a href="https://developers.google.com/j2objc">J2ObjC</a>
 *   <li>{@code NullPointerTester}, at least in the Android backport (where the type-use annotations

 *       where the {@code ...} contains the names of all the other {@code ParametricNullness}
 *       annotations in Guava. Or you might prefer to omit Guava from your {@code AnnotatedPackages}
 *       list.
 *   <li><a href="https://developers.google.com/j2objc">J2ObjC</a>
 *   <li>{@code NullPointerTester}, at least in the Android backport (where the type-use annotations

 * <p>Commonly used utilities include {@link Futures}, {@link MoreExecutors}, {@link
 * ThreadFactoryBuilder}, and {@link Uninterruptibles}.
 *
 * <p>This package is a part of the open-source <a href="https://github.com/google/guava">Guava</a>
 * library.
 */
@CheckReturnValue
@ParametersAreNonnullByDefault
package com.google.common.util.concurrent;

import com.google.errorprone.annotations.CheckReturnValue;

import java.util.NoSuchElementException;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * An iterator that supports a one-element lookahead while iterating.
 *
 * <p>See the Guava User Guide article on <a href=
 * "https://github.com/google/guava/wiki/CollectionHelpersExplained#peekingiterator">{@code
 * PeekingIterator}</a>.
 *
 * @author Mick Killianey
 * @since 2.0
 */
@DoNotMock("Use Iterators.peekingIterator")

/*
 * Copyright (C) 2009 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,