001 /* Iterator.java -- Interface for iterating over collections
002 Copyright (C) 1998, 2001, 2004, 2005 Free Software Foundation, Inc.
003
004 This file is part of GNU Classpath.
005
006 GNU Classpath is free software; you can redistribute it and/or modify
007 it under the terms of the GNU General Public License as published by
008 the Free Software Foundation; either version 2, or (at your option)
009 any later version.
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013 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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019 02110-1301 USA.
020
021 Linking this library statically or dynamically with other modules is
022 making a combined work based on this library. Thus, the terms and
023 conditions of the GNU General Public License cover the whole
024 combination.
025
026 As a special exception, the copyright holders of this library give you
027 permission to link this library with independent modules to produce an
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031 independent module, the terms and conditions of the license of that
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035 obligated to do so. If you do not wish to do so, delete this
036 exception statement from your version. */
037
038
039 package java.util;
040
041 /**
042 * An object which iterates over a collection. An Iterator is used to return
043 * the items once only, in sequence, by successive calls to the next method.
044 * It is also possible to remove elements from the underlying collection by
045 * using the optional remove method. Iterator is intended as a replacement
046 * for the Enumeration interface of previous versions of Java, which did not
047 * have the remove method and had less conveniently named methods.
048 *
049 * @author Original author unknown
050 * @author Eric Blake (ebb9@email.byu.edu)
051 * @see Collection
052 * @see ListIterator
053 * @see Enumeration
054 * @since 1.2
055 * @status updated to 1.4
056 */
057 public interface Iterator<E>
058 {
059 /**
060 * Tests whether there are elements remaining in the collection. In other
061 * words, calling <code>next()</code> will not throw an exception.
062 *
063 * @return true if there is at least one more element in the collection
064 */
065 boolean hasNext();
066
067 /**
068 * Obtain the next element in the collection.
069 *
070 * @return the next element in the collection
071 * @throws NoSuchElementException if there are no more elements
072 */
073 E next();
074
075 /**
076 * Remove from the underlying collection the last element returned by next
077 * (optional operation). This method can be called only once after each
078 * call to <code>next()</code>. It does not affect what will be returned
079 * by subsequent calls to next.
080 *
081 * @throws IllegalStateException if next has not yet been called or remove
082 * has already been called since the last call to next.
083 * @throws UnsupportedOperationException if this Iterator does not support
084 * the remove operation.
085 */
086 void remove();
087 }