001/* Iterator.java -- Interface for iterating over collections
002   Copyright (C) 1998, 2001, 2004, 2005 Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
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017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038
039package 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 */
057public 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}