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