1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.collections.iterators;
18
19 import java.lang.reflect.Array;
20 import java.util.ListIterator;
21 import java.util.NoSuchElementException;
22
23 import org.apache.commons.collections.ResettableListIterator;
24
25 /**
26 * Implements a {@link ListIterator} over an array.
27 * <p>
28 * The array can be either an array of object or of primitives. If you know
29 * that you have an object array, the {@link ObjectArrayListIterator}
30 * class is a better choice, as it will perform better.
31 *
32 * <p>
33 * This iterator does not support {@link #add(Object)} or {@link #remove()}, as the array
34 * cannot be changed in size. The {@link #set(Object)} method is supported however.
35 *
36 * @see org.apache.commons.collections.iterators.ArrayIterator
37 * @see java.util.Iterator
38 * @see java.util.ListIterator
39 *
40 * @since Commons Collections 3.0
41 * @version $Revision: 647116 $ $Date: 2008-04-11 12:23:08 +0100 (Fri, 11 Apr 2008) $
42 *
43 * @author Neil O'Toole
44 * @author Stephen Colebourne
45 * @author Phil Steitz
46 */
47 public class ArrayListIterator extends ArrayIterator
48 implements ListIterator, ResettableListIterator {
49
50 /**
51 * Holds the index of the last item returned by a call to <code>next()</code>
52 * or <code>previous()</code>. This is set to <code>-1</code> if neither method
53 * has yet been invoked. <code>lastItemIndex</code> is used to to implement
54 * the {@link #set} method.
55 *
56 */
57 protected int lastItemIndex = -1;
58
59 // Constructors
60 // ----------------------------------------------------------------------
61 /**
62 * Constructor for use with <code>setArray</code>.
63 * <p>
64 * Using this constructor, the iterator is equivalent to an empty iterator
65 * until {@link #setArray(Object)} is called to establish the array to iterate over.
66 */
67 public ArrayListIterator() {
68 super();
69 }
70
71 /**
72 * Constructs an ArrayListIterator that will iterate over the values in the
73 * specified array.
74 *
75 * @param array the array to iterate over
76 * @throws IllegalArgumentException if <code>array</code> is not an array.
77 * @throws NullPointerException if <code>array</code> is <code>null</code>
78 */
79 public ArrayListIterator(Object array) {
80 super(array);
81 }
82
83 /**
84 * Constructs an ArrayListIterator that will iterate over the values in the
85 * specified array from a specific start index.
86 *
87 * @param array the array to iterate over
88 * @param startIndex the index to start iterating at
89 * @throws IllegalArgumentException if <code>array</code> is not an array.
90 * @throws NullPointerException if <code>array</code> is <code>null</code>
91 * @throws IndexOutOfBoundsException if the start index is out of bounds
92 */
93 public ArrayListIterator(Object array, int startIndex) {
94 super(array, startIndex);
95 this.startIndex = startIndex;
96 }
97
98 /**
99 * Construct an ArrayListIterator that will iterate over a range of values
100 * in the specified array.
101 *
102 * @param array the array to iterate over
103 * @param startIndex the index to start iterating at
104 * @param endIndex the index (exclusive) to finish iterating at
105 * @throws IllegalArgumentException if <code>array</code> is not an array.
106 * @throws IndexOutOfBoundsException if the start or end index is out of bounds
107 * @throws IllegalArgumentException if end index is before the start
108 * @throws NullPointerException if <code>array</code> is <code>null</code>
109 */
110 public ArrayListIterator(Object array, int startIndex, int endIndex) {
111 super(array, startIndex, endIndex);
112 this.startIndex = startIndex;
113 }
114
115 // ListIterator interface
116 //-----------------------------------------------------------------------
117 /**
118 * Returns true if there are previous elements to return from the array.
119 *
120 * @return true if there is a previous element to return
121 */
122 public boolean hasPrevious() {
123 return (this.index > this.startIndex);
124 }
125
126 /**
127 * Gets the previous element from the array.
128 *
129 * @return the previous element
130 * @throws NoSuchElementException if there is no previous element
131 */
132 public Object previous() {
133 if (hasPrevious() == false) {
134 throw new NoSuchElementException();
135 }
136 this.lastItemIndex = --this.index;
137 return Array.get(this.array, this.index);
138 }
139
140 /**
141 * Gets the next element from the array.
142 *
143 * @return the next element
144 * @throws NoSuchElementException if there is no next element
145 */
146 public Object next() {
147 if (hasNext() == false) {
148 throw new NoSuchElementException();
149 }
150 this.lastItemIndex = this.index;
151 return Array.get(this.array, this.index++);
152 }
153
154 /**
155 * Gets the next index to be retrieved.
156 *
157 * @return the index of the item to be retrieved next
158 */
159 public int nextIndex() {
160 return this.index - this.startIndex;
161 }
162
163 /**
164 * Gets the index of the item to be retrieved if {@link #previous()} is called.
165 *
166 * @return the index of the item to be retrieved next
167 */
168 public int previousIndex() {
169 return this.index - this.startIndex - 1;
170 }
171
172 /**
173 * This iterator does not support modification of its backing collection, and so will
174 * always throw an {@link UnsupportedOperationException} when this method is invoked.
175 *
176 * @throws UnsupportedOperationException always thrown.
177 * @see java.util.ListIterator#set
178 */
179 public void add(Object o) {
180 throw new UnsupportedOperationException("add() method is not supported");
181 }
182
183 /**
184 * Sets the element under the cursor.
185 * <p>
186 * This method sets the element that was returned by the last call
187 * to {@link #next()} of {@link #previous()}.
188 * <p>
189 * <b>Note:</b> {@link ListIterator} implementations that support
190 * <code>add()</code> and <code>remove()</code> only allow <code>set()</code> to be called
191 * once per call to <code>next()</code> or <code>previous</code> (see the {@link ListIterator}
192 * javadoc for more details). Since this implementation does
193 * not support <code>add()</code> or <code>remove()</code>, <code>set()</code> may be
194 * called as often as desired.
195 *
196 * @see java.util.ListIterator#set
197 */
198 public void set(Object o) {
199 if (this.lastItemIndex == -1) {
200 throw new IllegalStateException("must call next() or previous() before a call to set()");
201 }
202
203 Array.set(this.array, this.lastItemIndex, o);
204 }
205
206 /**
207 * Resets the iterator back to the start index.
208 */
209 public void reset() {
210 super.reset();
211 this.lastItemIndex = -1;
212 }
213
214 }