    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 * @see org.apache.commons.collections4.iterators.ArrayIterator
    036 * @see java.util.Iterator
    037 * @see java.util.ListIterator
    038 *
    039 * @since 3.0
    040 */
    041public class ArrayListIterator<E> extends ArrayIterator<E>
    042        implements ResettableListIterator<E> {
    043
    044    /**
    045     * Holds the index of the last item returned by a call to <code>next()</code>
    046     * or <code>previous()</code>. This is set to <code>-1</code> if neither method
    047     * has yet been invoked. <code>lastItemIndex</code> is used to to implement
    048     * the {@link #set} method.
    049     */
    050    private int lastItemIndex = -1;
    051
    052    // Constructors
    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</code> is not an array.
    060     * @throws NullPointerException if <code>array</code> is <code>null</code>
    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</code> is not an array.
    073     * @throws NullPointerException if <code>array</code> is <code>null</code>
    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     * Construct 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</code> 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</code> is <code>null</code>
    091     */
    092    public ArrayListIterator(final Object array, final int startIndex, final int endIndex) {
    093        super(array, startIndex, endIndex);
    094    }
    095
    096    // ListIterator interface
    097    //-----------------------------------------------------------------------
    098    /**
    099     * Returns true if there are previous elements to return from the array.
    100     *
    101     * @return true if there is a previous element to return
    102     */
    103    @Override
    104    public boolean hasPrevious() {
    105        return this.index > this.startIndex;
    106    }
    107
    108    /**
    109     * Gets the previous element from the array.
    110     *
    111     * @return the previous element
    112     * @throws NoSuchElementException if there is no previous element
    113     */
    114    @Override
    115    @SuppressWarnings("unchecked")
    116    public E previous() {
    117        if (hasPrevious() == false) {
    118            throw new NoSuchElementException();
    119        }
    120        this.lastItemIndex = --this.index;
    121        return (E) Array.get(this.array, this.index);
    122    }
    123
    124    /**
    125     * Gets the next element from the array.
    126     *
    127     * @return the next element
    128     * @throws NoSuchElementException if there is no next element
    129     */
    130    @Override
    131    @SuppressWarnings("unchecked")
    132    public E next() {
    133        if (hasNext() == false) {
    134            throw new NoSuchElementException();
    135        }
    136        this.lastItemIndex = this.index;
    137        return (E) Array.get(this.array, this.index++);
    138    }
    139
    140    /**
    141     * Gets the next index to be retrieved.
    142     *
    143     * @return the index of the item to be retrieved next
    144     */
    145    @Override
    146    public int nextIndex() {
    147        return this.index - this.startIndex;
    148    }
    149
    150    /**
    151     * Gets the index of the item to be retrieved if {@link #previous()} is called.
    152     *
    153     * @return the index of the item to be retrieved next
    154     */
    155    @Override
    156    public int previousIndex() {
    157        return this.index - this.startIndex - 1;
    158    }
    159
    160    /**
    161     * This iterator does not support modification of its backing collection, and so will
    162     * always throw an {@link UnsupportedOperationException} when this method is invoked.
    163     *
    164     * @param o  the element to add
    165     * @throws UnsupportedOperationException always thrown.
    166     * @see java.util.ListIterator#set
    167     */
    168    @Override
    169    public void add(final Object o) {
    170        throw new UnsupportedOperationException("add() method is not supported");
    171    }
    172
    173    /**
    174     * Sets the element under the cursor.
    175     * <p>
    176     * This method sets the element that was returned by the last call
    177     * to {@link #next()} of {@link #previous()}.
    178     * <p>
    179     * <b>Note:</b> {@link java.util.ListIterator} implementations that support
    180     * <code>add()</code> and <code>remove()</code> only allow <code>set()</code> to be called
    181     * once per call to <code>next()</code> or <code>previous</code> (see the {@link java.util.ListIterator}
    182     * javadoc for more details). Since this implementation does
    183     * not support <code>add()</code> or <code>remove()</code>, <code>set()</code> may be
    184     * called as often as desired.
    185     *
    186     * @param o  the element to set
    187     * @throws IllegalStateException if {@link #next()} or {@link #previous()} has not been called
    188     * before {@link #set(Object)}
    189     * @see java.util.ListIterator#set
    190     */
    191    @Override
    192    public void set(final Object o) {
    193        if (this.lastItemIndex == -1) {
    194            throw new IllegalStateException("must call next() or previous() before a call to set()");
    195        }
    196
    197        Array.set(this.array, this.lastItemIndex, o);
    198    }
    199
    200    /**
    201     * Resets the iterator back to the start index.
    202     */
    203    @Override
    204    public void reset() {
    205        super.reset();
    206        this.lastItemIndex = -1;
    207    }
    208
    209}