/*
 * Copyright (C) 2008 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.Iterator;
import java.util.NoSuchElementException;

An iterator that supports a one-element lookahead while iterating.
See the Guava User Guide article on  
PeekingIterator.
Author:
Mick Killianey
Since:
2.0/**
 * 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
 */
@GwtCompatible
public interface PeekingIterator<E> extends Iterator<E> {
  
Returns the next element in the iteration, without advancing the iteration.
Calls to peek() should not change the state of the iteration, except that it may prevent removal of the most recent element via remove(). 
Throws:
NoSuchElementException – if the iteration has no more elements according to Iterator.hasNext()/**
   * Returns the next element in the iteration, without advancing the iteration.
   *
   * <p>Calls to {@code peek()} should not change the state of the iteration, except that it
   * <i>may</i> prevent removal of the most recent element via {@link #remove()}.
   *
   * @throws NoSuchElementException if the iteration has no more elements according to {@link
   *     #hasNext()}
   */
  E peek();

  
{@inheritDoc}
The objects returned by consecutive calls to peek() then next() are guaranteed to be equal to each other. /**
   * {@inheritDoc}
   *
   * <p>The objects returned by consecutive calls to {@link #peek()} then {@link #next()} are
   * guaranteed to be equal to each other.
   */
  @CanIgnoreReturnValue
  @Override
  E next();

  
{@inheritDoc}
Implementations may or may not support removal when a call to peek() has occurred since the most recent call to next(). 
Throws:
IllegalStateException – if there has been a call to peek() since the most recent call to next() and this implementation does not support this sequence of calls (optional)/**
   * {@inheritDoc}
   *
   * <p>Implementations may or may not support removal when a call to {@link #peek()} has occurred
   * since the most recent call to {@link #next()}.
   *
   * @throws IllegalStateException if there has been a call to {@link #peek()} since the most recent
   *     call to {@link #next()} and this implementation does not support this sequence of calls
   *     (optional)
   */
  @Override
  void remove();
}