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}