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