001    /*
002     *  Licensed to the Apache Software Foundation (ASF) under one or more
003     *  contributor license agreements.  See the NOTICE file distributed with
004     *  this work for additional information regarding copyright ownership.
005     *  The ASF licenses this file to You under the Apache License, Version 2.0
006     *  (the "License"); you may not use this file except in compliance with
007     *  the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     *  Unless required by applicable law or agreed to in writing, software
012     *  distributed under the License is distributed on an "AS IS" BASIS,
013     *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     *  See the License for the specific language governing permissions and
015     *  limitations under the License.
016     */
017    package org.apache.commons.collections.iterators;
018    
019    import java.lang.reflect.Array;
020    import java.util.ListIterator;
021    import java.util.NoSuchElementException;
022    
023    import org.apache.commons.collections.ResettableListIterator;
024    
025    /**
026     * Implements a {@link ListIterator} over an array. 
027     * <p>
028     * The array can be either an array of object or of primitives. If you know 
029     * that you have an object array, the {@link ObjectArrayListIterator}
030     * class is a better choice, as it will perform better.
031     * 
032     * <p>
033     * This iterator does not support {@link #add(Object)} or {@link #remove()}, as the array 
034     * cannot be changed in size. The {@link #set(Object)} method is supported however.
035     *
036     * @see org.apache.commons.collections.iterators.ArrayIterator
037     * @see java.util.Iterator
038     * @see java.util.ListIterator
039     *
040     * @since Commons Collections 3.0
041     * @version $Revision: 647116 $ $Date: 2008-04-11 12:23:08 +0100 (Fri, 11 Apr 2008) $
042     *
043     * @author Neil O'Toole
044     * @author Stephen Colebourne
045     * @author Phil Steitz
046     */
047    public class ArrayListIterator extends ArrayIterator
048            implements ListIterator, ResettableListIterator {
049    
050        /**
051         * Holds the index of the last item returned by a call to <code>next()</code>
052         * or <code>previous()</code>. This is set to <code>-1</code> if neither method
053         * has yet been invoked. <code>lastItemIndex</code> is used to to implement 
054         * the {@link #set} method.
055         *
056         */
057        protected int lastItemIndex = -1;
058    
059        // Constructors
060        // ----------------------------------------------------------------------
061        /**
062         * Constructor for use with <code>setArray</code>.
063         * <p>
064         * Using this constructor, the iterator is equivalent to an empty iterator
065         * until {@link #setArray(Object)} is  called to establish the array to iterate over.
066         */
067        public ArrayListIterator() {
068            super();
069        }
070    
071        /**
072         * Constructs an ArrayListIterator that will iterate over the values in the
073         * specified array.
074         *
075         * @param array the array to iterate over
076         * @throws IllegalArgumentException if <code>array</code> is not an array.
077         * @throws NullPointerException if <code>array</code> is <code>null</code>
078         */
079        public ArrayListIterator(Object array) {
080            super(array);
081        }
082    
083        /**
084         * Constructs an ArrayListIterator that will iterate over the values in the
085         * specified array from a specific start index.
086         *
087         * @param array  the array to iterate over
088         * @param startIndex  the index to start iterating at
089         * @throws IllegalArgumentException if <code>array</code> is not an array.
090         * @throws NullPointerException if <code>array</code> is <code>null</code>
091         * @throws IndexOutOfBoundsException if the start index is out of bounds
092         */
093        public ArrayListIterator(Object array, int startIndex) {
094            super(array, startIndex);
095            this.startIndex = startIndex;
096        }
097    
098        /**
099         * 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    }