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29 * The <code>Stack</code> class represents a last-in-first-out
30 * (LIFO) stack of objects. It extends class <tt>Vector</tt> with five
31 * operations that allow a vector to be treated as a stack. The usual
32 * <tt>push</tt> and <tt>pop</tt> operations are provided, as well as a
33 * method to <tt>peek</tt> at the top item on the stack, a method to test
34 * for whether the stack is <tt>empty</tt>, and a method to <tt>search</tt>
35 * the stack for an item and discover how far it is from the top.
37 * When a stack is first created, it contains no items.
39 * <p>A more complete and consistent set of LIFO stack operations is
40 * provided by the {@link Deque} interface and its implementations, which
41 * should be used in preference to this class. For example:
43 * Deque<Integer> stack = new ArrayDeque<Integer>();}</pre>
45 * @author Jonathan Payne
49 class Stack<E> extends Vector<E> {
51 * Creates an empty Stack.
57 * Pushes an item onto the top of this stack. This has exactly
60 * addElement(item)</pre></blockquote>
62 * @param item the item to be pushed onto this stack.
63 * @return the <code>item</code> argument.
64 * @see java.util.Vector#addElement
66 public E push(E item) {
73 * Removes the object at the top of this stack and returns that
74 * object as the value of this function.
76 * @return The object at the top of this stack (the last item
77 * of the <tt>Vector</tt> object).
78 * @throws EmptyStackException if this stack is empty.
80 public synchronized E pop() {
85 removeElementAt(len - 1);
91 * Looks at the object at the top of this stack without removing it
94 * @return the object at the top of this stack (the last item
95 * of the <tt>Vector</tt> object).
96 * @throws EmptyStackException if this stack is empty.
98 public synchronized E peek() {
102 throw new EmptyStackException();
103 return elementAt(len - 1);
107 * Tests if this stack is empty.
109 * @return <code>true</code> if and only if this stack contains
110 * no items; <code>false</code> otherwise.
112 public boolean empty() {
117 * Returns the 1-based position where an object is on this stack.
118 * If the object <tt>o</tt> occurs as an item in this stack, this
119 * method returns the distance from the top of the stack of the
120 * occurrence nearest the top of the stack; the topmost item on the
121 * stack is considered to be at distance <tt>1</tt>. The <tt>equals</tt>
122 * method is used to compare <tt>o</tt> to the
123 * items in this stack.
125 * @param o the desired object.
126 * @return the 1-based position from the top of the stack where
127 * the object is located; the return value <code>-1</code>
128 * indicates that the object is not on the stack.
130 public synchronized int search(Object o) {
131 int i = lastIndexOf(o);
139 /** use serialVersionUID from JDK 1.0.2 for interoperability */
140 private static final long serialVersionUID = 1224463164541339165L;