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.util.NoSuchElementException;
020
021import org.apache.commons.collections4.ResettableListIterator;
022
023/**
024 * Implements a {@link java.util.ListIterator} over an array of objects.
025 * <p>
026 * This iterator does not support {@link #add} or {@link #remove}, as the object array
027 * cannot be structurally modified. The {@link #set} method is supported however.
028 * </p>
029 * <p>
030 * The iterator implements a {@link #reset} method, allowing the reset of the iterator
031 * back to the start if required.
032 * </p>
033 *
034 * @param <E> the type of elements returned by this iterator.
035 * @see org.apache.commons.collections4.iterators.ObjectArrayIterator
036 * @see java.util.Iterator
037 * @see java.util.ListIterator
038 * @since 3.0
039 */
040public class ObjectArrayListIterator<E> extends ObjectArrayIterator<E>
041        implements ResettableListIterator<E> {
042
043    /**
044     * Holds the index of the last item returned by a call to {@code next()}
045     * or {@code previous()}. This is set to {@code -1} if neither method
046     * has yet been invoked. {@code lastItemIndex} is used to implement the
047     * {@link #set} method.
048     */
049    private int lastItemIndex = -1;
050
051    /**
052     * Constructs an ObjectArrayListIterator that will iterate over the values in the
053     * specified array.
054     *
055     * @param array the array to iterate over
056     * @throws NullPointerException if {@code array} is {@code null}
057     */
058    public ObjectArrayListIterator(final E... array) {
059        super(array);
060    }
061
062    /**
063     * Constructs an ObjectArrayListIterator that will iterate over the values in the
064     * specified array from a specific start index.
065     *
066     * @param array  the array to iterate over
067     * @param start  the index to start iterating at
068     * @throws NullPointerException if {@code array} is {@code null}
069     * @throws IndexOutOfBoundsException if the start index is out of bounds
070     */
071    public ObjectArrayListIterator(final E[] array, final int start) {
072        super(array, start);
073    }
074
075    /**
076     * Constructs an ObjectArrayListIterator that will iterate over a range of values
077     * in the specified array.
078     *
079     * @param array  the array to iterate over
080     * @param start  the index to start iterating at
081     * @param end  the index (exclusive) to finish iterating at
082     * @throws IndexOutOfBoundsException if the start or end index is out of bounds
083     * @throws IllegalArgumentException if end index is before the start
084     * @throws NullPointerException if {@code array} is {@code null}
085     */
086    public ObjectArrayListIterator(final E[] array, final int start, final int end) {
087        super(array, start, end);
088    }
089
090    /**
091     * This iterator does not support modification of its backing array's size, and so will
092     * always throw an {@link UnsupportedOperationException} when this method is invoked.
093     *
094     * @param obj  the object to add
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 java.util.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 java.util.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}