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.
010    
011    GNU Classpath is distributed in the hope that it will be useful, but
012    WITHOUT ANY WARRANTY; without even the implied warranty of
013    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014    General Public License for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
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    }