    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.list;
    018
    019import java.util.ArrayList;
    020import java.util.Collection;
    021import java.util.Collections;
    022import java.util.List;
    023
    024/**
    025 * Decorates another {@code List} to make it seamlessly grow when
    026 * indices larger than the list size are used on add and set,
    027 * avoiding most IndexOutOfBoundsExceptions.
    028 * <p>
    029 * This class avoids errors by growing when a set or add method would
    030 * normally throw an IndexOutOfBoundsException.
    031 * Note that IndexOutOfBoundsException IS returned for invalid negative indices.
    032 * </p>
    033 * <p>
    034 * Trying to set or add to an index larger than the size will cause the list
    035 * to grow (using {@code null} elements). Clearly, care must be taken
    036 * not to use excessively large indices, as the internal list will grow to
    037 * match.
    038 * </p>
    039 * <p>
    040 * Trying to use any method other than add or set with an invalid index will
    041 * call the underlying list and probably result in an IndexOutOfBoundsException.
    042 * </p>
    043 * <p>
    044 * Take care when using this list with {@code null} values, as
    045 * {@code null} is the value added when growing the list.
    046 * </p>
    047 * <p>
    048 * All sub-lists will access the underlying list directly, and will throw
    049 * IndexOutOfBoundsExceptions.
    050 * </p>
    051 * <p>
    052 * This class differs from {@link LazyList} because here growth occurs on
    053 * set and add, where {@code LazyList} grows on get. However, they
    054 * can be used together by decorating twice.
    055 * </p>
    056 *
    057 * @see LazyList
    058 * @since 3.2
    059 */
    060public class GrowthList<E> extends AbstractSerializableListDecorator<E> {
    061
    062    /** Serialization version */
    063    private static final long serialVersionUID = -3620001881672L;
    064
    065    /**
    066     * Factory method to create a growth list.
    067     *
    068     * @param <E> the type of the elements in the list
    069     * @param list  the list to decorate, must not be null
    070     * @return a new growth list
    071     * @throws NullPointerException if list is null
    072     * @since 4.0
    073     */
    074    public static <E> GrowthList<E> growthList(final List<E> list) {
    075        return new GrowthList<>(list);
    076    }
    077
    078    /**
    079     * Constructor that uses an ArrayList internally.
    080     */
    081    public GrowthList() {
    082        super(new ArrayList<>());
    083    }
    084
    085    /**
    086     * Constructor that uses an ArrayList internally.
    087     *
    088     * @param initialCapacity  the initial capacity of the ArrayList
    089     * @throws IllegalArgumentException if initial capacity is invalid
    090     */
    091    public GrowthList(final int initialCapacity) {
    092        super(new ArrayList<>(initialCapacity));
    093    }
    094
    095    /**
    096     * Constructor that wraps (not copies).
    097     *
    098     * @param list  the list to decorate, must not be null
    099     * @throws NullPointerException if list is null
    100     */
    101    protected GrowthList(final List<E> list) {
    102        super(list);
    103    }
    104
    105    /**
    106     * Decorate the add method to perform the growth behavior.
    107     * <p>
    108     * If the requested index is greater than the current size, the list will
    109     * grow to the new size. Indices between the old size and the requested
    110     * size will be filled with {@code null}.
    111     * <p>
    112     * If the index is less than the current size, the value will be added to
    113     * the underlying list directly.
    114     * If the index is less than zero, the underlying list is called, which
    115     * will probably throw an IndexOutOfBoundsException.
    116     *
    117     * @param index  the index to add at
    118     * @param element  the object to add at the specified index
    119     * @throws UnsupportedOperationException if the underlying list doesn't implement set
    120     * @throws ClassCastException if the underlying list rejects the element
    121     * @throws IllegalArgumentException if the underlying list rejects the element
    122     */
    123    @Override
    124    public void add(final int index, final E element) {
    125        final int size = decorated().size();
    126        if (index > size) {
    127            decorated().addAll(Collections.<E>nCopies(index - size, null));
    128        }
    129        decorated().add(index, element);
    130    }
    131
    132    /**
    133     * Decorate the addAll method to perform the growth behavior.
    134     * <p>
    135     * If the requested index is greater than the current size, the list will
    136     * grow to the new size. Indices between the old size and the requested
    137     * size will be filled with {@code null}.
    138     * <p>
    139     * If the index is less than the current size, the values will be added to
    140     * the underlying list directly.
    141     * If the index is less than zero, the underlying list is called, which
    142     * will probably throw an IndexOutOfBoundsException.
    143     *
    144     * @param index  the index to add at
    145     * @param coll  the collection to add at the specified index
    146     * @return true if the list changed
    147     * @throws UnsupportedOperationException if the underlying list doesn't implement set
    148     * @throws ClassCastException if the underlying list rejects the element
    149     * @throws IllegalArgumentException if the underlying list rejects the element
    150     */
    151    @Override
    152    public boolean addAll(final int index, final Collection<? extends E> coll) {
    153        final int size = decorated().size();
    154        boolean result = false;
    155        if (index > size) {
    156            decorated().addAll(Collections.<E>nCopies(index - size, null));
    157            result = true;
    158        }
    159        return decorated().addAll(index, coll) || result;
    160    }
    161
    162    /**
    163     * Decorate the set method to perform the growth behavior.
    164     * <p>
    165     * If the requested index is greater than the current size, the list will
    166     * grow to the new size. Indices between the old size and the requested
    167     * size will be filled with {@code null}.
    168     * <p>
    169     * If the index is less than the current size, the value will be set onto
    170     * the underlying list directly.
    171     * If the index is less than zero, the underlying list is called, which
    172     * will probably throw an IndexOutOfBoundsException.
    173     *
    174     * @param index  the index to set
    175     * @param element  the object to set at the specified index
    176     * @return the object previously at that index
    177     * @throws UnsupportedOperationException if the underlying list doesn't implement set
    178     * @throws ClassCastException if the underlying list rejects the element
    179     * @throws IllegalArgumentException if the underlying list rejects the element
    180     */
    181    @Override
    182    public E set(final int index, final E element) {
    183        final int size = decorated().size();
    184        if (index >= size) {
    185            decorated().addAll(Collections.<E>nCopies(index - size + 1, null));
    186        }
    187        return decorated().set(index, element);
    188    }
    189
    190}