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;
018
019 import java.util.ArrayList;
020 import java.util.EmptyStackException;
021
022 /**
023 * An implementation of the {@link java.util.Stack} API that is based on an
024 * <code>ArrayList</code> instead of a <code>Vector</code>, so it is not
025 * synchronized to protect against multi-threaded access. The implementation
026 * is therefore operates faster in environments where you do not need to
027 * worry about multiple thread contention.
028 * <p>
029 * The removal order of an <code>ArrayStack</code> is based on insertion
030 * order: The most recently added element is removed first. The iteration
031 * order is <i>not</i> the same as the removal order. The iterator returns
032 * elements from the bottom up, whereas the {@link #remove()} method removes
033 * them from the top down.
034 * <p>
035 * Unlike <code>Stack</code>, <code>ArrayStack</code> accepts null entries.
036 * <p>
037 * <strong>Note:</strong> this class should be bytecode-identical to the
038 * version in commons collections. This is required to allow backwards
039 * compability with both previous versions of BeanUtils and also allow
040 * coexistance with both collections 2.1 and 3.0.
041 *
042 * @see java.util.Stack
043 * @since Commons Collections 1.0
044 * @version $Revision: 555824 $ $Date: 2007-07-13 01:27:15 +0100 (Fri, 13 Jul 2007) $
045 *
046 * @author Craig R. McClanahan
047 * @author Paul Jack
048 * @author Stephen Colebourne
049 */
050 public class ArrayStack extends ArrayList implements Buffer {
051
052 /** Ensure serialization compatibility */
053 private static final long serialVersionUID = 2130079159931574599L;
054
055 /**
056 * Constructs a new empty <code>ArrayStack</code>. The initial size
057 * is controlled by <code>ArrayList</code> and is currently 10.
058 */
059 public ArrayStack() {
060 super();
061 }
062
063 /**
064 * Constructs a new empty <code>ArrayStack</code> with an initial size.
065 *
066 * @param initialSize the initial size to use
067 * @throws IllegalArgumentException if the specified initial size
068 * is negative
069 */
070 public ArrayStack(int initialSize) {
071 super(initialSize);
072 }
073
074 /**
075 * Return <code>true</code> if this stack is currently empty.
076 * <p>
077 * This method exists for compatibility with <code>java.util.Stack</code>.
078 * New users of this class should use <code>isEmpty</code> instead.
079 *
080 * @return true if the stack is currently empty
081 */
082 public boolean empty() {
083 return isEmpty();
084 }
085
086 /**
087 * Returns the top item off of this stack without removing it.
088 *
089 * @return the top item on the stack
090 * @throws EmptyStackException if the stack is empty
091 */
092 public Object peek() throws EmptyStackException {
093 int n = size();
094 if (n <= 0) {
095 throw new EmptyStackException();
096 } else {
097 return get(n - 1);
098 }
099 }
100
101 /**
102 * Returns the n'th item down (zero-relative) from the top of this
103 * stack without removing it.
104 *
105 * @param n the number of items down to go
106 * @return the n'th item on the stack, zero relative
107 * @throws EmptyStackException if there are not enough items on the
108 * stack to satisfy this request
109 */
110 public Object peek(int n) throws EmptyStackException {
111 int m = (size() - n) - 1;
112 if (m < 0) {
113 throw new EmptyStackException();
114 } else {
115 return get(m);
116 }
117 }
118
119 /**
120 * Pops the top item off of this stack and return it.
121 *
122 * @return the top item on the stack
123 * @throws EmptyStackException if the stack is empty
124 */
125 public Object pop() throws EmptyStackException {
126 int n = size();
127 if (n <= 0) {
128 throw new EmptyStackException();
129 } else {
130 return remove(n - 1);
131 }
132 }
133
134 /**
135 * Pushes a new item onto the top of this stack. The pushed item is also
136 * returned. This is equivalent to calling <code>add</code>.
137 *
138 * @param item the item to be added
139 * @return the item just pushed
140 */
141 public Object push(Object item) {
142 add(item);
143 return item;
144 }
145
146 /**
147 * Returns the one-based position of the distance from the top that the
148 * specified object exists on this stack, where the top-most element is
149 * considered to be at distance <code>1</code>. If the object is not
150 * present on the stack, return <code>-1</code> instead. The
151 * <code>equals()</code> method is used to compare to the items
152 * in this stack.
153 *
154 * @param object the object to be searched for
155 * @return the 1-based depth into the stack of the object, or -1 if not found
156 */
157 public int search(Object object) {
158 int i = size() - 1; // Current index
159 int n = 1; // Current distance
160 while (i >= 0) {
161 Object current = get(i);
162 if ((object == null && current == null) ||
163 (object != null && object.equals(current))) {
164 return n;
165 }
166 i--;
167 n++;
168 }
169 return -1;
170 }
171
172 /**
173 * Returns the element on the top of the stack.
174 *
175 * @return the element on the top of the stack
176 * @throws BufferUnderflowException if the stack is empty
177 */
178 public Object get() {
179 int size = size();
180 if (size == 0) {
181 throw new BufferUnderflowException();
182 }
183 return get(size - 1);
184 }
185
186 /**
187 * Removes the element on the top of the stack.
188 *
189 * @return the removed element
190 * @throws BufferUnderflowException if the stack is empty
191 */
192 public Object remove() {
193 int size = size();
194 if (size == 0) {
195 throw new BufferUnderflowException();
196 }
197 return remove(size - 1);
198 }
199
200 }