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| 1 | /* | ||
| 2 | * Copyright (c) 1997, 2007, Oracle and/or its affiliates. All rights reserved. | ||
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 4 | * | ||
| 5 | * This code is free software; you can redistribute it and/or modify it | ||
| 6 | * under the terms of the GNU General Public License version 2 only, as | ||
| 7 | * published by the Free Software Foundation. Oracle designates this | ||
| 8 | * particular file as subject to the "Classpath" exception as provided | ||
| 9 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 10 | * | ||
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 14 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 15 | * accompanied this code). | ||
| 16 | * | ||
| 17 | * You should have received a copy of the GNU General Public License version | ||
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 20 | * | ||
| 21 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 22 | * or visit www.oracle.com if you need additional information or have any | ||
| 23 | * questions. | ||
| 24 | */ | ||
| 25 | |||
| 26 | package java.util; | ||
| 27 | |||
| 28 | /** | ||
| 29 | * An iterator for lists that allows the programmer | ||
| 30 | * to traverse the list in either direction, modify | ||
| 31 | * the list during iteration, and obtain the iterator's | ||
| 32 | * current position in the list. A {@code ListIterator} | ||
| 33 | * has no current element; its <I>cursor position</I> always | ||
| 34 | * lies between the element that would be returned by a call | ||
| 35 | * to {@code previous()} and the element that would be | ||
| 36 | * returned by a call to {@code next()}. | ||
| 37 | * An iterator for a list of length {@code n} has {@code n+1} possible | ||
| 38 | * cursor positions, as illustrated by the carets ({@code ^}) below: | ||
| 39 | * <PRE> | ||
| 40 | * Element(0) Element(1) Element(2) ... Element(n-1) | ||
| 41 | * cursor positions: ^ ^ ^ ^ ^ | ||
| 42 | * </PRE> | ||
| 43 | * Note that the {@link #remove} and {@link #set(Object)} methods are | ||
| 44 | * <i>not</i> defined in terms of the cursor position; they are defined to | ||
| 45 | * operate on the last element returned by a call to {@link #next} or | ||
| 46 | * {@link #previous()}. | ||
| 47 | * | ||
| 48 | * <p>This interface is a member of the | ||
| 49 | * <a href="{@docRoot}/../technotes/guides/collections/index.html"> | ||
| 50 | * Java Collections Framework</a>. | ||
| 51 | * | ||
| 52 | * @author Josh Bloch | ||
| 53 | * @see Collection | ||
| 54 | * @see List | ||
| 55 | * @see Iterator | ||
| 56 | * @see Enumeration | ||
| 57 | * @see List#listIterator() | ||
| 58 | * @since 1.2 | ||
| 59 | */ | ||
| 60 | public interface ListIterator<E> extends Iterator<E> { | ||
| 61 | // Query Operations | ||
| 62 | |||
| 63 | /** | ||
| 64 | * Returns {@code true} if this list iterator has more elements when | ||
| 65 | * traversing the list in the forward direction. (In other words, | ||
| 66 | * returns {@code true} if {@link #next} would return an element rather | ||
| 67 | * than throwing an exception.) | ||
| 68 | * | ||
| 69 | * @return {@code true} if the list iterator has more elements when | ||
| 70 | * traversing the list in the forward direction | ||
| 71 | */ | ||
| 72 | boolean hasNext(); | ||
| 73 | |||
| 74 | /** | ||
| 75 | * Returns the next element in the list and advances the cursor position. | ||
| 76 | * This method may be called repeatedly to iterate through the list, | ||
| 77 | * or intermixed with calls to {@link #previous} to go back and forth. | ||
| 78 | * (Note that alternating calls to {@code next} and {@code previous} | ||
| 79 | * will return the same element repeatedly.) | ||
| 80 | * | ||
| 81 | * @return the next element in the list | ||
| 82 | * @throws NoSuchElementException if the iteration has no next element | ||
| 83 | */ | ||
| 84 | E next(); | ||
| 85 | |||
| 86 | /** | ||
| 87 | * Returns {@code true} if this list iterator has more elements when | ||
| 88 | * traversing the list in the reverse direction. (In other words, | ||
| 89 | * returns {@code true} if {@link #previous} would return an element | ||
| 90 | * rather than throwing an exception.) | ||
| 91 | * | ||
| 92 | * @return {@code true} if the list iterator has more elements when | ||
| 93 | * traversing the list in the reverse direction | ||
| 94 | */ | ||
| 95 | boolean hasPrevious(); | ||
| 96 | |||
| 97 | /** | ||
| 98 | * Returns the previous element in the list and moves the cursor | ||
| 99 | * position backwards. This method may be called repeatedly to | ||
| 100 | * iterate through the list backwards, or intermixed with calls to | ||
| 101 | * {@link #next} to go back and forth. (Note that alternating calls | ||
| 102 | * to {@code next} and {@code previous} will return the same | ||
| 103 | * element repeatedly.) | ||
| 104 | * | ||
| 105 | * @return the previous element in the list | ||
| 106 | * @throws NoSuchElementException if the iteration has no previous | ||
| 107 | * element | ||
| 108 | */ | ||
| 109 | E previous(); | ||
| 110 | |||
| 111 | /** | ||
| 112 | * Returns the index of the element that would be returned by a | ||
| 113 | * subsequent call to {@link #next}. (Returns list size if the list | ||
| 114 | * iterator is at the end of the list.) | ||
| 115 | * | ||
| 116 | * @return the index of the element that would be returned by a | ||
| 117 | * subsequent call to {@code next}, or list size if the list | ||
| 118 | * iterator is at the end of the list | ||
| 119 | */ | ||
| 120 | int nextIndex(); | ||
| 121 | |||
| 122 | /** | ||
| 123 | * Returns the index of the element that would be returned by a | ||
| 124 | * subsequent call to {@link #previous}. (Returns -1 if the list | ||
| 125 | * iterator is at the beginning of the list.) | ||
| 126 | * | ||
| 127 | * @return the index of the element that would be returned by a | ||
| 128 | * subsequent call to {@code previous}, or -1 if the list | ||
| 129 | * iterator is at the beginning of the list | ||
| 130 | */ | ||
| 131 | int previousIndex(); | ||
| 132 | |||
| 133 | |||
| 134 | // Modification Operations | ||
| 135 | |||
| 136 | /** | ||
| 137 | * Removes from the list the last element that was returned by {@link | ||
| 138 | * #next} or {@link #previous} (optional operation). This call can | ||
| 139 | * only be made once per call to {@code next} or {@code previous}. | ||
| 140 | * It can be made only if {@link #add} has not been | ||
| 141 | * called after the last call to {@code next} or {@code previous}. | ||
| 142 | * | ||
| 143 | * @throws UnsupportedOperationException if the {@code remove} | ||
| 144 | * operation is not supported by this list iterator | ||
| 145 | * @throws IllegalStateException if neither {@code next} nor | ||
| 146 | * {@code previous} have been called, or {@code remove} or | ||
| 147 | * {@code add} have been called after the last call to | ||
| 148 | * {@code next} or {@code previous} | ||
| 149 | */ | ||
| 150 | void remove(); | ||
| 151 | |||
| 152 | /** | ||
| 153 | * Replaces the last element returned by {@link #next} or | ||
| 154 | * {@link #previous} with the specified element (optional operation). | ||
| 155 | * This call can be made only if neither {@link #remove} nor {@link | ||
| 156 | * #add} have been called after the last call to {@code next} or | ||
| 157 | * {@code previous}. | ||
| 158 | * | ||
| 159 | * @param e the element with which to replace the last element returned by | ||
| 160 | * {@code next} or {@code previous} | ||
| 161 | * @throws UnsupportedOperationException if the {@code set} operation | ||
| 162 | * is not supported by this list iterator | ||
| 163 | * @throws ClassCastException if the class of the specified element | ||
| 164 | * prevents it from being added to this list | ||
| 165 | * @throws IllegalArgumentException if some aspect of the specified | ||
| 166 | * element prevents it from being added to this list | ||
| 167 | * @throws IllegalStateException if neither {@code next} nor | ||
| 168 | * {@code previous} have been called, or {@code remove} or | ||
| 169 | * {@code add} have been called after the last call to | ||
| 170 | * {@code next} or {@code previous} | ||
| 171 | */ | ||
| 172 | void set(E e); | ||
| 173 | |||
| 174 | /** | ||
| 175 | * Inserts the specified element into the list (optional operation). | ||
| 176 | * The element is inserted immediately before the element that | ||
| 177 | * would be returned by {@link #next}, if any, and after the element | ||
| 178 | * that would be returned by {@link #previous}, if any. (If the | ||
| 179 | * list contains no elements, the new element becomes the sole element | ||
| 180 | * on the list.) The new element is inserted before the implicit | ||
| 181 | * cursor: a subsequent call to {@code next} would be unaffected, and a | ||
| 182 | * subsequent call to {@code previous} would return the new element. | ||
| 183 | * (This call increases by one the value that would be returned by a | ||
| 184 | * call to {@code nextIndex} or {@code previousIndex}.) | ||
| 185 | * | ||
| 186 | * @param e the element to insert | ||
| 187 | * @throws UnsupportedOperationException if the {@code add} method is | ||
| 188 | * not supported by this list iterator | ||
| 189 | * @throws ClassCastException if the class of the specified element | ||
| 190 | * prevents it from being added to this list | ||
| 191 | * @throws IllegalArgumentException if some aspect of this element | ||
| 192 | * prevents it from being added to this list | ||
| 193 | */ | ||
| 194 | void add(E e); | ||
| 195 | } | ||