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 *
037 * @see java.util.Stack
038 * @since Commons Collections 1.0
039 * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
040 *
041 * @author Craig R. McClanahan
042 * @author Paul Jack
043 * @author Stephen Colebourne
044 */
045 public class ArrayStack extends ArrayList implements Buffer {
046
047 /** Ensure serialization compatibility */
048 private static final long serialVersionUID = 2130079159931574599L;
049
050 /**
051 * Constructs a new empty <code>ArrayStack</code>. The initial size
052 * is controlled by <code>ArrayList</code> and is currently 10.
053 */
054 public ArrayStack() {
055 super();
056 }
057
058 /**
059 * Constructs a new empty <code>ArrayStack</code> with an initial size.
060 *
061 * @param initialSize the initial size to use
062 * @throws IllegalArgumentException if the specified initial size
063 * is negative
064 */
065 public ArrayStack(int initialSize) {
066 super(initialSize);
067 }
068
069 /**
070 * Return <code>true</code> if this stack is currently empty.
071 * <p>
072 * This method exists for compatibility with <code>java.util.Stack</code>.
073 * New users of this class should use <code>isEmpty</code> instead.
074 *
075 * @return true if the stack is currently empty
076 */
077 public boolean empty() {
078 return isEmpty();
079 }
080
081 /**
082 * Returns the top item off of this stack without removing it.
083 *
084 * @return the top item on the stack
085 * @throws EmptyStackException if the stack is empty
086 */
087 public Object peek() throws EmptyStackException {
088 int n = size();
089 if (n <= 0) {
090 throw new EmptyStackException();
091 } else {
092 return get(n - 1);
093 }
094 }
095
096 /**
097 * Returns the n'th item down (zero-relative) from the top of this
098 * stack without removing it.
099 *
100 * @param n the number of items down to go
101 * @return the n'th item on the stack, zero relative
102 * @throws EmptyStackException if there are not enough items on the
103 * stack to satisfy this request
104 */
105 public Object peek(int n) throws EmptyStackException {
106 int m = (size() - n) - 1;
107 if (m < 0) {
108 throw new EmptyStackException();
109 } else {
110 return get(m);
111 }
112 }
113
114 /**
115 * Pops the top item off of this stack and return it.
116 *
117 * @return the top item on the stack
118 * @throws EmptyStackException if the stack is empty
119 */
120 public Object pop() throws EmptyStackException {
121 int n = size();
122 if (n <= 0) {
123 throw new EmptyStackException();
124 } else {
125 return remove(n - 1);
126 }
127 }
128
129 /**
130 * Pushes a new item onto the top of this stack. The pushed item is also
131 * returned. This is equivalent to calling <code>add</code>.
132 *
133 * @param item the item to be added
134 * @return the item just pushed
135 */
136 public Object push(Object item) {
137 add(item);
138 return item;
139 }
140
141 /**
142 * Returns the one-based position of the distance from the top that the
143 * specified object exists on this stack, where the top-most element is
144 * considered to be at distance <code>1</code>. If the object is not
145 * present on the stack, return <code>-1</code> instead. The
146 * <code>equals()</code> method is used to compare to the items
147 * in this stack.
148 *
149 * @param object the object to be searched for
150 * @return the 1-based depth into the stack of the object, or -1 if not found
151 */
152 public int search(Object object) {
153 int i = size() - 1; // Current index
154 int n = 1; // Current distance
155 while (i >= 0) {
156 Object current = get(i);
157 if ((object == null && current == null) ||
158 (object != null && object.equals(current))) {
159 return n;
160 }
161 i--;
162 n++;
163 }
164 return -1;
165 }
166
167 /**
168 * Returns the element on the top of the stack.
169 *
170 * @return the element on the top of the stack
171 * @throws BufferUnderflowException if the stack is empty
172 */
173 public Object get() {
174 int size = size();
175 if (size == 0) {
176 throw new BufferUnderflowException();
177 }
178 return get(size - 1);
179 }
180
181 /**
182 * Removes the element on the top of the stack.
183 *
184 * @return the removed element
185 * @throws BufferUnderflowException if the stack is empty
186 */
187 public Object remove() {
188 int size = size();
189 if (size == 0) {
190 throw new BufferUnderflowException();
191 }
192 return remove(size - 1);
193 }
194
195 }