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