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