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 *      https://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.ListIterator;
021import java.util.NoSuchElementException;
022
023import org.apache.commons.collections4.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 * </p>
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 * </p>
036 *
037 * @param <E> The type of elements returned by this iterator.
038 * @see org.apache.commons.collections4.iterators.ArrayIterator
039 * @see java.util.Iterator
040 * @see java.util.ListIterator
041 * @since 3.0
042 */
043public class ArrayListIterator<E> extends ArrayIterator<E>
044        implements ResettableListIterator<E> {
045
046    /**
047     * Holds the index of the last item returned by a call to {@code next()}
048     * or {@code previous()}. This is set to {@code -1} if neither method
049     * has yet been invoked. {@code lastItemIndex} is used to implement
050     * the {@link #set} method.
051     */
052    private int lastItemIndex = -1;
053
054    /**
055     * Constructs an ArrayListIterator that will iterate over the values in the
056     * specified array.
057     *
058     * @param array The array to iterate over
059     * @throws IllegalArgumentException if {@code array} is not an array.
060     * @throws NullPointerException if {@code array} is {@code null}
061     */
062    public ArrayListIterator(final Object array) {
063        super(array);
064    }
065
066    /**
067     * Constructs an ArrayListIterator that will iterate over the values in the
068     * specified array from a specific start index.
069     *
070     * @param array  The array to iterate over
071     * @param startIndex  The index to start iterating at
072     * @throws IllegalArgumentException if {@code array} is not an array.
073     * @throws NullPointerException if {@code array} is {@code null}
074     * @throws IndexOutOfBoundsException if the start index is out of bounds
075     */
076    public ArrayListIterator(final Object array, final int startIndex) {
077        super(array, startIndex);
078    }
079
080    /**
081     * Constructs an ArrayListIterator that will iterate over a range of values
082     * in the specified array.
083     *
084     * @param array  The array to iterate over
085     * @param startIndex  The index to start iterating at
086     * @param endIndex  The index (exclusive) to finish iterating at
087     * @throws IllegalArgumentException if {@code array} is not an array.
088     * @throws IndexOutOfBoundsException if the start or end index is out of bounds
089     * @throws IllegalArgumentException if end index is before the start
090     * @throws NullPointerException if {@code array} is {@code null}
091     */
092    public ArrayListIterator(final Object array, final int startIndex, final int endIndex) {
093        super(array, startIndex, endIndex);
094    }
095
096    /**
097     * This iterator does not support modification of its backing collection, and so will
098     * always throw an {@link UnsupportedOperationException} when this method is invoked.
099     *
100     * @param o  The element to add
101     * @throws UnsupportedOperationException always thrown.
102     * @see java.util.ListIterator#set
103     */
104    @Override
105    public void add(final Object o) {
106        throw new UnsupportedOperationException("add() method is not supported");
107    }
108
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 index > 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        lastItemIndex = index;
132        return (E) Array.get(array, 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 index - 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        lastItemIndex = --index;
158        return (E) Array.get(array, 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 index - 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        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     * <p>
187     * <strong>Note:</strong> {@link ListIterator} implementations that support
188     * {@code add()} and {@code remove()} only allow {@code set()} to be called
189     * once per call to {@code next()} or {@code previous} (see the {@link ListIterator}
190     * Javadoc for more details). Since this implementation does
191     * not support {@code add()} or {@code remove()}, {@code set()} may be
192     * called as often as desired.
193     * </p>
194     *
195     * @param o  The element to set
196     * @throws IllegalStateException if {@link #next()} or {@link #previous()} has not been called
197     * before {@link #set(Object)}
198     * @see java.util.ListIterator#set
199     */
200    @Override
201    public void set(final Object o) {
202        if (lastItemIndex == -1) {
203            throw new IllegalStateException("must call next() or previous() before a call to set()");
204        }
205
206        Array.set(array, lastItemIndex, o);
207    }
208
209}