    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.lang.reflect.Array;
    020import java.util.ListIterator;
    021import java.util.NoSuchElementException;
    022
    023import org.apache.commons.collections4.ResettableListIterator;
    024
    025/**
    026 * Implements a {@link ListIterator} over an array.
    027 * <p>
    028 * The array can be either an array of object or of primitives. If you know
    029 * that you have an object array, the {@link ObjectArrayListIterator}
    030 * class is a better choice, as it will perform better.
    031 * </p>
    032 * <p>
    033 * This iterator does not support {@link #add(Object)} or {@link #remove()}, as the array
    034 * cannot be changed in size. The {@link #set(Object)} method is supported however.
    035 * </p>
    036 *
    037 * @param <E> The type of elements returned by this iterator.
    038 * @see org.apache.commons.collections4.iterators.ArrayIterator
    039 * @see java.util.Iterator
    040 * @see java.util.ListIterator
    041 * @since 3.0
    042 */
    043public class ArrayListIterator<E> extends ArrayIterator<E>
    044        implements ResettableListIterator<E> {
    045
    046    /**
    047     * Holds the index of the last item returned by a call to {@code next()}
    048     * or {@code previous()}. This is set to {@code -1} if neither method
    049     * has yet been invoked. {@code lastItemIndex} is used to implement
    050     * the {@link #set} method.
    051     */
    052    private int lastItemIndex = -1;
    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} is not an array.
    060     * @throws NullPointerException if {@code array} is {@code null}
    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} is not an array.
    073     * @throws NullPointerException if {@code array} is {@code null}
    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     * Constructs 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} 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} is {@code null}
    091     */
    092    public ArrayListIterator(final Object array, final int startIndex, final int endIndex) {
    093        super(array, startIndex, endIndex);
    094    }
    095
    096    /**
    097     * This iterator does not support modification of its backing collection, and so will
    098     * always throw an {@link UnsupportedOperationException} when this method is invoked.
    099     *
    100     * @param o  The element to add
    101     * @throws UnsupportedOperationException always thrown.
    102     * @see java.util.ListIterator#set
    103     */
    104    @Override
    105    public void add(final Object o) {
    106        throw new UnsupportedOperationException("add() method is not supported");
    107    }
    108
    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 index > 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        lastItemIndex = index;
    132        return (E) Array.get(array, 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 index - 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        lastItemIndex = --index;
    158        return (E) Array.get(array, 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 index - 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        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     * <p>
    187     * <strong>Note:</strong> {@link ListIterator} implementations that support
    188     * {@code add()} and {@code remove()} only allow {@code set()} to be called
    189     * once per call to {@code next()} or {@code previous} (see the {@link ListIterator}
    190     * Javadoc for more details). Since this implementation does
    191     * not support {@code add()} or {@code remove()}, {@code set()} may be
    192     * called as often as desired.
    193     * </p>
    194     *
    195     * @param o  The element to set
    196     * @throws IllegalStateException if {@link #next()} or {@link #previous()} has not been called
    197     * before {@link #set(Object)}
    198     * @see java.util.ListIterator#set
    199     */
    200    @Override
    201    public void set(final Object o) {
    202        if (lastItemIndex == -1) {
    203            throw new IllegalStateException("must call next() or previous() before a call to set()");
    204        }
    205
    206        Array.set(array, lastItemIndex, o);
    207    }
    208
    209}