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