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/*
* 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.
*
* <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.
*
* <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}
*
* <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}
*
* <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();
}
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