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16 package org.apache.commons.collections;
17
18 import java.util.ArrayList;
19 import java.util.EmptyStackException;
20
21 /**
22 * An implementation of the {@link java.util.Stack} API that is based on an
23 * <code>ArrayList</code> instead of a <code>Vector</code>, so it is not
24 * synchronized to protect against multi-threaded access. The implementation
25 * is therefore operates faster in environments where you do not need to
26 * worry about multiple thread contention.
27 * <p>
28 * The removal order of an <code>ArrayStack</code> is based on insertion
29 * order: The most recently added element is removed first. The iteration
30 * order is <i>not</i> the same as the removal order. The iterator returns
31 * elements from the bottom up, whereas the {@link #remove()} method removes
32 * them from the top down.
33 * <p>
34 * Unlike <code>Stack</code>, <code>ArrayStack</code> accepts null entries.
35 * <p>
36 * <strong>Note:</strong> this class should be bytecode-identical to the
37 * version in commons collections. This is required to allow backwards
38 * compability with both previous versions of BeanUtils and also allow
39 * coexistance with both collections 2.1 and 3.0.
40 *
41 * @see java.util.Stack
42 * @since Commons Collections 1.0
43 * @version $Revision: 1.1 $ $Date: 2004/05/10 19:50:13 $
44 *
45 * @author Craig R. McClanahan
46 * @author Paul Jack
47 * @author Stephen Colebourne
48 */
49 public class ArrayStack extends ArrayList implements Buffer {
50
51 /** Ensure serialization compatibility */
52 private static final long serialVersionUID = 2130079159931574599L;
53
54 /**
55 * Constructs a new empty <code>ArrayStack</code>. The initial size
56 * is controlled by <code>ArrayList</code> and is currently 10.
57 */
58 public ArrayStack() {
59 super();
60 }
61
62 /**
63 * Constructs a new empty <code>ArrayStack</code> with an initial size.
64 *
65 * @param initialSize the initial size to use
66 * @throws IllegalArgumentException if the specified initial size
67 * is negative
68 */
69 public ArrayStack(int initialSize) {
70 super(initialSize);
71 }
72
73 /**
74 * Return <code>true</code> if this stack is currently empty.
75 * <p>
76 * This method exists for compatibility with <code>java.util.Stack</code>.
77 * New users of this class should use <code>isEmpty</code> instead.
78 *
79 * @return true if the stack is currently empty
80 */
81 public boolean empty() {
82 return isEmpty();
83 }
84
85 /**
86 * Returns the top item off of this stack without removing it.
87 *
88 * @return the top item on the stack
89 * @throws EmptyStackException if the stack is empty
90 */
91 public Object peek() throws EmptyStackException {
92 int n = size();
93 if (n <= 0) {
94 throw new EmptyStackException();
95 } else {
96 return get(n - 1);
97 }
98 }
99
100 /**
101 * Returns the n'th item down (zero-relative) from the top of this
102 * stack without removing it.
103 *
104 * @param n the number of items down to go
105 * @return the n'th item on the stack, zero relative
106 * @throws EmptyStackException if there are not enough items on the
107 * stack to satisfy this request
108 */
109 public Object peek(int n) throws EmptyStackException {
110 int m = (size() - n) - 1;
111 if (m < 0) {
112 throw new EmptyStackException();
113 } else {
114 return get(m);
115 }
116 }
117
118 /**
119 * Pops the top item off of this stack and return it.
120 *
121 * @return the top item on the stack
122 * @throws EmptyStackException if the stack is empty
123 */
124 public Object pop() throws EmptyStackException {
125 int n = size();
126 if (n <= 0) {
127 throw new EmptyStackException();
128 } else {
129 return remove(n - 1);
130 }
131 }
132
133 /**
134 * Pushes a new item onto the top of this stack. The pushed item is also
135 * returned. This is equivalent to calling <code>add</code>.
136 *
137 * @param item the item to be added
138 * @return the item just pushed
139 */
140 public Object push(Object item) {
141 add(item);
142 return item;
143 }
144
145 /**
146 * Returns the one-based position of the distance from the top that the
147 * specified object exists on this stack, where the top-most element is
148 * considered to be at distance <code>1</code>. If the object is not
149 * present on the stack, return <code>-1</code> instead. The
150 * <code>equals()</code> method is used to compare to the items
151 * in this stack.
152 *
153 * @param object the object to be searched for
154 * @return the 1-based depth into the stack of the object, or -1 if not found
155 */
156 public int search(Object object) {
157 int i = size() - 1;
158 int n = 1;
159 while (i >= 0) {
160 Object current = get(i);
161 if ((object == null && current == null) ||
162 (object != null && object.equals(current))) {
163 return n;
164 }
165 i--;
166 n++;
167 }
168 return -1;
169 }
170
171 /**
172 * Returns the element on the top of the stack.
173 *
174 * @return the element on the top of the stack
175 * @throws BufferUnderflowException if the stack is empty
176 */
177 public Object get() {
178 int size = size();
179 if (size == 0) {
180 throw new BufferUnderflowException();
181 }
182 return get(size - 1);
183 }
184
185 /**
186 * Removes the element on the top of the stack.
187 *
188 * @return the removed element
189 * @throws BufferUnderflowException if the stack is empty
190 */
191 public Object remove() {
192 int size = size();
193 if (size == 0) {
194 throw new BufferUnderflowException();
195 }
196 return remove(size - 1);
197 }
198
199 }