001/* ListIterator.java -- Extended Iterator for iterating over ordered lists
002   Copyright (C) 1998, 1999, 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
016You should have received a copy of the GNU General Public License
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 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 */
062public 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}