1 /* 2 * Copyright (C) 2008 The Guava Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.common.collect; 18 19 import com.google.common.annotations.GwtCompatible; 20 21 import java.util.Iterator; 22 import java.util.NoSuchElementException; 23 24 /** 25 * An iterator that supports a one-element lookahead while iterating. 26 * 27 * <p>See the Guava User Guide article on <a href= 28 * "http://code.google.com/p/guava-libraries/wiki/CollectionHelpersExplained#PeekingIterator"> 29 * {@code PeekingIterator}</a>. 30 * 31 * @author Mick Killianey 32 * @since 2.0 (imported from Google Collections Library) 33 */ 34 @GwtCompatible 35 public interface PeekingIterator<E> extends Iterator<E> { 36 /** 37 * Returns the next element in the iteration, without advancing the iteration. 38 * 39 * <p>Calls to {@code peek()} should not change the state of the iteration, 40 * except that it <i>may</i> prevent removal of the most recent element via 41 * {@link #remove()}. 42 * 43 * @throws NoSuchElementException if the iteration has no more elements 44 * according to {@link #hasNext()} 45 */ 46 E peek(); 47 48 /** 49 * {@inheritDoc} 50 * 51 * <p>The objects returned by consecutive calls to {@link #peek()} then {@link 52 * #next()} are guaranteed to be equal to each other. 53 */ 54 @Override 55 E next(); 56 57 /** 58 * {@inheritDoc} 59 * 60 * <p>Implementations may or may not support removal when a call to {@link 61 * #peek()} has occurred since the most recent call to {@link #next()}. 62 * 63 * @throws IllegalStateException if there has been a call to {@link #peek()} 64 * since the most recent call to {@link #next()} and this implementation 65 * does not support this sequence of calls (optional) 66 */ 67 @Override 68 void remove(); 69 } 70
