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 }