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17 package org.apache.commons.collections;
18
19 import java.util.ArrayList;
20 import java.util.EmptyStackException;
21
22 /***
23 * An implementation of the {@link java.util.Stack} API that is based on an
24 * <code>ArrayList</code> instead of a <code>Vector</code>, so it is not
25 * synchronized to protect against multi-threaded access. The implementation
26 * is therefore operates faster in environments where you do not need to
27 * worry about multiple thread contention.
28 * <p>
29 * The removal order of an <code>ArrayStack</code> is based on insertion
30 * order: The most recently added element is removed first. The iteration
31 * order is <i>not</i> the same as the removal order. The iterator returns
32 * elements from the bottom up, whereas the {@link #remove()} method removes
33 * them from the top down.
34 * <p>
35 * Unlike <code>Stack</code>, <code>ArrayStack</code> accepts null entries.
36 * <p>
37 * <strong>Note:</strong> this class should be bytecode-identical to the
38 * version in commons collections. This is required to allow backwards
39 * compability with both previous versions of BeanUtils and also allow
40 * coexistance with both collections 2.1 and 3.0.
41 *
42 * @see java.util.Stack
43 * @since Commons Collections 1.0
44 * @version $Revision: 555824 $ $Date: 2007-07-13 01:27:15 +0100 (Fri, 13 Jul 2007) $
45 *
46 * @author Craig R. McClanahan
47 * @author Paul Jack
48 * @author Stephen Colebourne
49 */
50 public class ArrayStack extends ArrayList implements Buffer {
51
52 /*** Ensure serialization compatibility */
53 private static final long serialVersionUID = 2130079159931574599L;
54
55 /***
56 * Constructs a new empty <code>ArrayStack</code>. The initial size
57 * is controlled by <code>ArrayList</code> and is currently 10.
58 */
59 public ArrayStack() {
60 super();
61 }
62
63 /***
64 * Constructs a new empty <code>ArrayStack</code> with an initial size.
65 *
66 * @param initialSize the initial size to use
67 * @throws IllegalArgumentException if the specified initial size
68 * is negative
69 */
70 public ArrayStack(int initialSize) {
71 super(initialSize);
72 }
73
74 /***
75 * Return <code>true</code> if this stack is currently empty.
76 * <p>
77 * This method exists for compatibility with <code>java.util.Stack</code>.
78 * New users of this class should use <code>isEmpty</code> instead.
79 *
80 * @return true if the stack is currently empty
81 */
82 public boolean empty() {
83 return isEmpty();
84 }
85
86 /***
87 * Returns the top item off of this stack without removing it.
88 *
89 * @return the top item on the stack
90 * @throws EmptyStackException if the stack is empty
91 */
92 public Object peek() throws EmptyStackException {
93 int n = size();
94 if (n <= 0) {
95 throw new EmptyStackException();
96 } else {
97 return get(n - 1);
98 }
99 }
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;
159 int n = 1;
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 }