001    /* ListIterator.java -- Extended Iterator for iterating over ordered lists
002       Copyright (C) 1998, 1999, 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
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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 extended version of Iterator to support the extra features of Lists. The
043     * elements may be accessed in forward or reverse order, elements may be
044     * replaced as well as removed, and new elements may be inserted, during the
045     * traversal of the list.
046     * <p>
047     *
048     * A list with n elements provides n+1 iterator positions (the front, the end,
049     * or between two elements). Note that <code>remove</code> and <code>set</code>
050     * operate on the last element returned, whether it was by <code>next</code>
051     * or <code>previous</code>.
052     *
053     * @author Original author unknown
054     * @author Eric Blake (ebb9@email.byu.edu)
055     * @see Collection
056     * @see List
057     * @see Iterator
058     * @see Enumeration
059     * @since 1.2
060     * @status updated to 1.4
061     */
062    public interface ListIterator<E> extends Iterator<E>
063    {
064      /**
065       * Tests whether there are elements remaining in the list in the forward
066       * direction. In other words, next() will not fail with a
067       * NoSuchElementException.
068       *
069       * @return true if the list continues in the forward direction
070       */
071      boolean hasNext();
072    
073      /**
074       * Tests whether there are elements remaining in the list in the reverse
075       * direction. In other words, previous() will not fail with a
076       * NoSuchElementException.
077       *
078       * @return true if the list continues in the reverse direction
079       */
080      boolean hasPrevious();
081    
082      /**
083       * Obtain the next element in the list in the forward direction. Repeated
084       * calls to next may be used to iterate over the entire list, or calls to
085       * next and previous may be used together to go forwards and backwards.
086       * Alternating calls to next and previous will return the same element.
087       *
088       * @return the next element in the list in the forward direction
089       * @throws NoSuchElementException if there are no more elements
090       */
091      E next();
092    
093      /**
094       * Obtain the next element in the list in the reverse direction. Repeated
095       * calls to previous may be used to iterate backwards over the entire list,
096       * or calls to next and previous may be used together to go forwards and
097       * backwards. Alternating calls to next and previous will return the same
098       * element.
099       *
100       * @return the next element in the list in the reverse direction
101       * @throws NoSuchElementException if there are no more elements
102       */
103      E previous();
104    
105      /**
106       * Find the index of the element that would be returned by a call to next.
107       * If hasNext() returns false, this returns the list size.
108       *
109       * @return the index of the element that would be returned by next()
110       */
111      int nextIndex();
112    
113      /**
114       * Find the index of the element that would be returned by a call to
115       * previous. If hasPrevious() returns false, this returns -1.
116       *
117       * @return the index of the element that would be returned by previous()
118       */
119      int previousIndex();
120    
121      /**
122       * Insert an element into the list at the current position of the iterator
123       * (optional operation). The element is inserted in between the element that
124       * would be returned by previous and the element that would be returned by
125       * next. After the insertion, a subsequent call to next is unaffected, but
126       * a call to previous returns the item that was added. The values returned
127       * by nextIndex() and previousIndex() are incremented.
128       *
129       * @param o the object to insert into the list
130       * @throws ClassCastException if the object is of a type which cannot be added
131       *         to this list.
132       * @throws IllegalArgumentException if some other aspect of the object stops
133       *         it being added to this list.
134       * @throws UnsupportedOperationException if this ListIterator does not
135       *         support the add operation.
136       */
137      void add(E o);
138    
139      /**
140       * Remove from the list the element last returned by a call to next or
141       * previous (optional operation). This method may only be called if neither
142       * add nor remove have been called since the last call to next or previous.
143       *
144       * @throws IllegalStateException if neither next or previous have been
145       *         called, or if add or remove has been called since the last call
146       *         to next or previous
147       * @throws UnsupportedOperationException if this ListIterator does not
148       *         support the remove operation
149       */
150      void remove();
151    
152      /**
153       * Replace the element last returned by a call to next or previous with a
154       * given object (optional operation). This method may only be called if
155       * neither add nor remove have been called since the last call to next or
156       * previous.
157       *
158       * @param o the object to replace the element with
159       * @throws ClassCastException the object is of a type which cannot be added
160       *         to this list
161       * @throws IllegalArgumentException some other aspect of the object stops
162       *         it being added to this list
163       * @throws IllegalStateException if neither next or previous have been
164       *         called, or if add or remove has been called since the last call
165       *         to next or previous
166       * @throws UnsupportedOperationException if this ListIterator does not
167       *         support the set operation
168       */
169      void set(E o);
170    }