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     */
017    package org.apache.commons.collections.list;
018    
019    import java.util.ArrayList;
020    import java.util.Collection;
021    import java.util.Collections;
022    import java.util.List;
023    
024    /**
025     * Decorates another <code>List</code> 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     * Trying to set or add to an index larger than the size will cause the list
034     * to grow (using <code>null</code> elements). Clearly, care must be taken
035     * not to use excessively large indices, as the internal list will grow to
036     * match.
037     * <p>
038     * Trying to use any method other than add or set with an invalid index will
039     * call the underlying list and probably result in an IndexOutOfBoundsException.
040     * <p>
041     * Take care when using this list with <code>null</code> values, as
042     * <code>null</code> is the value added when growing the list.
043     * <p>
044     * All sub-lists will access the underlying list directly, and will throw
045     * IndexOutOfBoundsExceptions.
046     * <p>
047     * This class differs from {@link LazyList} because here growth occurs on
048     * set and add, where <code>LazyList</code> grows on get. However, they
049     * can be used together by decorating twice.
050     *
051     * @see LazyList
052     * @since Commons Collections 3.2
053     * @version $Revision: 155406 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
054     *
055     * @author Stephen Colebourne
056     * @author Paul Legato
057     */
058    public class GrowthList extends AbstractSerializableListDecorator {
059    
060        /** Serialization version */
061        private static final long serialVersionUID = -3620001881672L;
062    
063        /**
064         * Factory method to create a growth list.
065         *
066         * @param list  the list to decorate, must not be null
067         * @throws IllegalArgumentException if list is null
068         */
069        public static List decorate(List list) {
070            return new GrowthList(list);
071        }
072    
073        //-----------------------------------------------------------------------
074        /**
075         * Constructor that uses an ArrayList internally.
076         */
077        public GrowthList() {
078            super(new ArrayList());
079        }
080    
081        /**
082         * Constructor that uses an ArrayList internally.
083         *
084         * @param initialSize  the initial size of the ArrayList
085         * @throws IllegalArgumentException if initial size is invalid
086         */
087        public GrowthList(int initialSize) {
088            super(new ArrayList(initialSize));
089        }
090    
091        /**
092         * Constructor that wraps (not copies).
093         *
094         * @param list  the list to decorate, must not be null
095         * @throws IllegalArgumentException if list is null
096         */
097        protected GrowthList(List list) {
098            super(list);
099        }
100    
101        //-----------------------------------------------------------------------
102        /**
103         * Decorate the add method to perform the growth behaviour.
104         * <p>
105         * If the requested index is greater than the current size, the list will
106         * grow to the new size. Indices between the old size and the requested
107         * size will be filled with <code>null</code>.
108         * <p>
109         * If the index is less than the current size, the value will be added to
110         * the underlying list directly.
111         * If the index is less than zero, the underlying list is called, which
112         * will probably throw an IndexOutOfBoundsException.
113         *
114         * @param index  the index to add at
115         * @param element  the object to add at the specified index
116         * @throws UnsupportedOperationException if the underlying list doesn't implement set
117         * @throws ClassCastException if the underlying list rejects the element
118         * @throws IllegalArgumentException if the underlying list rejects the element
119         */
120        public void add(int index, Object element) {
121            int size = getList().size();
122            if (index > size) {
123                getList().addAll(Collections.nCopies(index - size, null));
124            }
125            getList().add(index, element);
126        }
127    
128        //-----------------------------------------------------------------------
129        /**
130         * Decorate the addAll method to perform the growth behaviour.
131         * <p>
132         * If the requested index is greater than the current size, the list will
133         * grow to the new size. Indices between the old size and the requested
134         * size will be filled with <code>null</code>.
135         * <p>
136         * If the index is less than the current size, the values will be added to
137         * the underlying list directly.
138         * If the index is less than zero, the underlying list is called, which
139         * will probably throw an IndexOutOfBoundsException.
140         *
141         * @param index  the index to add at
142         * @param coll  the collection to add at the specified index
143         * @return true if the list changed
144         * @throws UnsupportedOperationException if the underlying list doesn't implement set
145         * @throws ClassCastException if the underlying list rejects the element
146         * @throws IllegalArgumentException if the underlying list rejects the element
147         */
148        public boolean addAll(int index, Collection coll) {
149            int size = getList().size();
150            boolean result = false;
151            if (index > size) {
152                getList().addAll(Collections.nCopies(index - size, null));
153                result = true;
154            }
155            return (getList().addAll(index, coll) | result);
156        }
157    
158        //-----------------------------------------------------------------------
159        /**
160         * Decorate the set method to perform the growth behaviour.
161         * <p>
162         * If the requested index is greater than the current size, the list will
163         * grow to the new size. Indices between the old size and the requested
164         * size will be filled with <code>null</code>.
165         * <p>
166         * If the index is less than the current size, the value will be set onto
167         * the underlying list directly.
168         * If the index is less than zero, the underlying list is called, which
169         * will probably throw an IndexOutOfBoundsException.
170         *
171         * @param index  the index to set
172         * @param element  the object to set at the specified index
173         * @return the object previously at that index
174         * @throws UnsupportedOperationException if the underlying list doesn't implement set
175         * @throws ClassCastException if the underlying list rejects the element
176         * @throws IllegalArgumentException if the underlying list rejects the element
177         */
178        public Object set(int index, Object element) {
179            int size = getList().size();
180            if (index >= size) {
181                getList().addAll(Collections.nCopies((index - size) + 1, null));
182            }
183            return getList().set(index, element);
184        }
185    
186    }