    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 * @see org.apache.commons.collections4.iterators.ObjectArrayIterator
    033 * @see java.util.Iterator
    034 * @see java.util.ListIterator
    035 *
    036 * @since 3.0
    037 */
    038public class ObjectArrayListIterator<E> extends ObjectArrayIterator<E>
    039        implements ResettableListIterator<E> {
    040
    041    /**
    042     * Holds the index of the last item returned by a call to <code>next()</code>
    043     * or <code>previous()</code>. This is set to <code>-1</code> if neither method
    044     * has yet been invoked. <code>lastItemIndex</code> is used to to implement the
    045     * {@link #set} method.
    046     */
    047    private int lastItemIndex = -1;
    048
    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</code> is <code>null</code>
    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</code> is <code>null</code>
    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     * Construct 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</code> is <code>null</code>
    084     */
    085    public ObjectArrayListIterator(final E[] array, final int start, final int end) {
    086        super(array, start, end);
    087    }
    088
    089    // ListIterator interface
    090    //-------------------------------------------------------------------------
    091
    092    /**
    093     * Returns true if there are previous elements to return from the array.
    094     *
    095     * @return true if there is a previous element to return
    096     */
    097    @Override
    098    public boolean hasPrevious() {
    099        return this.index > getStartIndex();
    100    }
    101
    102    /**
    103     * Gets the previous element from the array.
    104     *
    105     * @return the previous element
    106     * @throws NoSuchElementException if there is no previous element
    107     */
    108    @Override
    109    public E previous() {
    110        if (hasPrevious() == false) {
    111            throw new NoSuchElementException();
    112        }
    113        this.lastItemIndex = --this.index;
    114        return this.array[this.index];
    115    }
    116
    117    /**
    118     * Gets the next element from the array.
    119     *
    120     * @return the next element
    121     * @throws NoSuchElementException if there is no next element
    122     */
    123    @Override
    124    public E next() {
    125        if (hasNext() == false) {
    126            throw new NoSuchElementException();
    127        }
    128        this.lastItemIndex = this.index;
    129        return this.array[this.index++];
    130    }
    131
    132    /**
    133     * Gets the next index to be retrieved.
    134     *
    135     * @return the index of the item to be retrieved next
    136     */
    137    @Override
    138    public int nextIndex() {
    139        return this.index - getStartIndex();
    140    }
    141
    142    /**
    143     * Gets the index of the item to be retrieved if {@link #previous()} is called.
    144     *
    145     * @return the index of the item to be retrieved next
    146     */
    147    @Override
    148    public int previousIndex() {
    149        return this.index - getStartIndex() - 1;
    150    }
    151
    152    /**
    153     * This iterator does not support modification of its backing array's size, and so will
    154     * always throw an {@link UnsupportedOperationException} when this method is invoked.
    155     *
    156     * @param obj  the object to add
    157     * @throws UnsupportedOperationException always thrown.
    158     */
    159    @Override
    160    public void add(final E obj) {
    161        throw new UnsupportedOperationException("add() method is not supported");
    162    }
    163
    164    /**
    165     * Sets the element under the cursor.
    166     * <p>
    167     * This method sets the element that was returned by the last call
    168     * to {@link #next()} of {@link #previous()}.
    169     *
    170     * <b>Note:</b> {@link java.util.ListIterator} implementations that support <code>add()</code>
    171     * and <code>remove()</code> only allow <code>set()</code> to be called once per call
    172     * to <code>next()</code> or <code>previous</code> (see the {@link java.util.ListIterator}
    173     * javadoc for more details). Since this implementation does not support
    174     * <code>add()</code> or <code>remove()</code>, <code>set()</code> may be
    175     * called as often as desired.
    176     *
    177     * @param obj  the object to set into the array
    178     * @throws IllegalStateException if next() has not yet been called.
    179     * @throws ClassCastException if the object type is unsuitable for the array
    180     */
    181    @Override
    182    public void set(final E obj) {
    183        if (this.lastItemIndex == -1) {
    184            throw new IllegalStateException("must call next() or previous() before a call to set()");
    185        }
    186
    187        this.array[this.lastItemIndex] = obj;
    188    }
    189
    190    /**
    191     * Resets the iterator back to the start index.
    192     */
    193    @Override
    194    public void reset() {
    195        super.reset();
    196        this.lastItemIndex = -1;
    197    }
    198
    199}