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 */
017package org.apache.commons.collections4.iterators;
018
019import java.lang.reflect.Array;
020import java.util.NoSuchElementException;
021
022import org.apache.commons.collections4.ResettableListIterator;
023
024/**
025 * Implements a {@link java.util.ListIterator} over an array.
026 * <p>
027 * The array can be either an array of object or of primitives. If you know
028 * that you have an object array, the {@link ObjectArrayListIterator}
029 * class is a better choice, as it will perform better.
030 *
031 * <p>
032 * This iterator does not support {@link #add(Object)} or {@link #remove()}, as the array
033 * cannot be changed in size. The {@link #set(Object)} method is supported however.
034 *
035 * @param <E> the type of elements returned by this iterator.
036 * @see org.apache.commons.collections4.iterators.ArrayIterator
037 * @see java.util.Iterator
038 * @see java.util.ListIterator
039 *
040 * @since 3.0
041 */
042public class ArrayListIterator<E> extends ArrayIterator<E>
043        implements ResettableListIterator<E> {
044
045    /**
046     * Holds the index of the last item returned by a call to {@code next()}
047     * or {@code previous()}. This is set to {@code -1} if neither method
048     * has yet been invoked. {@code lastItemIndex} is used to implement
049     * the {@link #set} method.
050     */
051    private int lastItemIndex = -1;
052
053    /**
054     * Constructs an ArrayListIterator that will iterate over the values in the
055     * specified array.
056     *
057     * @param array the array to iterate over
058     * @throws IllegalArgumentException if {@code array} is not an array.
059     * @throws NullPointerException if {@code array} is {@code null}
060     */
061    public ArrayListIterator(final Object array) {
062        super(array);
063    }
064
065    /**
066     * Constructs an ArrayListIterator that will iterate over the values in the
067     * specified array from a specific start index.
068     *
069     * @param array  the array to iterate over
070     * @param startIndex  the index to start iterating at
071     * @throws IllegalArgumentException if {@code array} is not an array.
072     * @throws NullPointerException if {@code array} is {@code null}
073     * @throws IndexOutOfBoundsException if the start index is out of bounds
074     */
075    public ArrayListIterator(final Object array, final int startIndex) {
076        super(array, startIndex);
077    }
078
079    /**
080     * Constructs an ArrayListIterator that will iterate over a range of values
081     * in the specified array.
082     *
083     * @param array  the array to iterate over
084     * @param startIndex  the index to start iterating at
085     * @param endIndex  the index (exclusive) to finish iterating at
086     * @throws IllegalArgumentException if {@code array} is not an array.
087     * @throws IndexOutOfBoundsException if the start or end index is out of bounds
088     * @throws IllegalArgumentException if end index is before the start
089     * @throws NullPointerException if {@code array} is {@code null}
090     */
091    public ArrayListIterator(final Object array, final int startIndex, final int endIndex) {
092        super(array, startIndex, endIndex);
093    }
094
095    /**
096     * This iterator does not support modification of its backing collection, and so will
097     * always throw an {@link UnsupportedOperationException} when this method is invoked.
098     *
099     * @param o  the element to add
100     * @throws UnsupportedOperationException always thrown.
101     * @see java.util.ListIterator#set
102     */
103    @Override
104    public void add(final Object o) {
105        throw new UnsupportedOperationException("add() method is not supported");
106    }
107
108    // ListIterator interface
109    /**
110     * Returns true if there are previous elements to return from the array.
111     *
112     * @return true if there is a previous element to return
113     */
114    @Override
115    public boolean hasPrevious() {
116        return this.index > this.startIndex;
117    }
118
119    /**
120     * Gets the next element from the array.
121     *
122     * @return the next element
123     * @throws NoSuchElementException if there is no next element
124     */
125    @Override
126    @SuppressWarnings("unchecked")
127    public E next() {
128        if (!hasNext()) {
129            throw new NoSuchElementException();
130        }
131        this.lastItemIndex = this.index;
132        return (E) Array.get(this.array, this.index++);
133    }
134
135    /**
136     * Gets the next index to be retrieved.
137     *
138     * @return the index of the item to be retrieved next
139     */
140    @Override
141    public int nextIndex() {
142        return this.index - this.startIndex;
143    }
144
145    /**
146     * Gets the previous element from the array.
147     *
148     * @return the previous element
149     * @throws NoSuchElementException if there is no previous element
150     */
151    @Override
152    @SuppressWarnings("unchecked")
153    public E previous() {
154        if (!hasPrevious()) {
155            throw new NoSuchElementException();
156        }
157        this.lastItemIndex = --this.index;
158        return (E) Array.get(this.array, this.index);
159    }
160
161    /**
162     * Gets the index of the item to be retrieved if {@link #previous()} is called.
163     *
164     * @return the index of the item to be retrieved next
165     */
166    @Override
167    public int previousIndex() {
168        return this.index - this.startIndex - 1;
169    }
170
171    /**
172     * Resets the iterator back to the start index.
173     */
174    @Override
175    public void reset() {
176        super.reset();
177        this.lastItemIndex = -1;
178    }
179
180    /**
181     * Sets the element under the cursor.
182     * <p>
183     * This method sets the element that was returned by the last call
184     * to {@link #next()} of {@link #previous()}.
185     * <p>
186     * <b>Note:</b> {@link java.util.ListIterator} implementations that support
187     * {@code add()} and {@code remove()} only allow {@code set()} to be called
188     * once per call to {@code next()} or {@code previous} (see the {@link java.util.ListIterator}
189     * Javadoc for more details). Since this implementation does
190     * not support {@code add()} or {@code remove()}, {@code set()} may be
191     * called as often as desired.
192     *
193     * @param o  the element to set
194     * @throws IllegalStateException if {@link #next()} or {@link #previous()} has not been called
195     * before {@link #set(Object)}
196     * @see java.util.ListIterator#set
197     */
198    @Override
199    public void set(final Object o) {
200        if (this.lastItemIndex == -1) {
201            throw new IllegalStateException("must call next() or previous() before a call to set()");
202        }
203
204        Array.set(this.array, this.lastItemIndex, o);
205    }
206
207}