java/util/Stack.java

/*
 * %W% %E%
 *
 * Copyright 2005 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package java.util;

/**
 * The <code>Stack</code> class represents a last-in-first-out
 * (LIFO) stack of objects. It extends class <tt>Vector</tt> with five
 * operations that allow a vector to be treated as a stack. The usual
 * <tt>push</tt> and <tt>pop</tt> operations are provided, as well as a
 * method to <tt>peek</tt> at the top item on the stack, a method to test
 * for whether the stack is <tt>empty</tt>, and a method to <tt>search</tt>
 * the stack for an item and discover how far it is from the top.
 * <p>
 * When a stack is first created, it contains no items.
 *
 * <p>A more complete and consistent set of LIFO stack operations is
 * provided by the {@link Deque} interface and its implementations, which
 * should be used in preference to this class.  For example:
 * <pre>   {@code
 *   Deque<Integer> stack = new ArrayDeque<Integer>();}</pre>
 *
 * @author  Jonathan Payne
 * @version %I%, %G%
 * @since   JDK1.0
 */
public
class Stack<E> extends Vector<E> {
    /**
     * Creates an empty Stack.
     */
    public Stack() {
    }

    /**
     * Pushes an item onto the top of this stack. This has exactly
     * the same effect as:
     * <blockquote><pre>
     * addElement(item)</pre></blockquote>
     *
     * @param   item   the item to be pushed onto this stack.
     * @return  the <code>item</code> argument.
     * @see     java.util.Vector#addElement
     */
    public E push(E item) {
        addElement(item);

        return item;
    }

    /**
     * Removes the object at the top of this stack and returns that
     * object as the value of this function.
     *
     * @return     The object at the top of this stack (the last item
     *             of the <tt>Vector</tt> object).
     * @exception  EmptyStackException  if this stack is empty.
     */
    public synchronized E pop() {
        E       obj;
        int     len = size();

        obj = peek();
        removeElementAt(len - 1);

        return obj;
    }

    /**
     * Looks at the object at the top of this stack without removing it
     * from the stack.
     *
     * @return     the object at the top of this stack (the last item
     *             of the <tt>Vector</tt> object).
     * @exception  EmptyStackException  if this stack is empty.
     */
    public synchronized E peek() {
        int     len = size();

        if (len == 0)
            throw new EmptyStackException();
        return elementAt(len - 1);
    }

    /**
     * Tests if this stack is empty.
     *
     * @return  <code>true</code> if and only if this stack contains
     *          no items; <code>false</code> otherwise.
     */
    public boolean empty() {
        return size() == 0;
    }

    /**
     * Returns the 1-based position where an object is on this stack.
     * If the object <tt>o</tt> occurs as an item in this stack, this
     * method returns the distance from the top of the stack of the
     * occurrence nearest the top of the stack; the topmost item on the
     * stack is considered to be at distance <tt>1</tt>. The <tt>equals</tt>
     * method is used to compare <tt>o</tt> to the
     * items in this stack.
     *
     * @param   o   the desired object.
     * @return  the 1-based position from the top of the stack where
     *          the object is located; the return value <code>-1</code>
     *          indicates that the object is not on the stack.
     */
    public synchronized int search(Object o) {
        int i = lastIndexOf(o);

        if (i >= 0) {
            return size() - i;
        }
        return -1;
    }

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = 1224463164541339165L;
}
Revision:	1.3
Committed:	Sat Oct 1 22:07:26 2005 UTC (18 years, 7 months ago) by jsr166
Branch:	MAIN
Changes since 1.2:	+26 -27 lines
Log Message:	minor rewording
#	User	Rev	Content
1	dl	1.1	/*
2	jsr166	1.2	* %W% %E%
3	dl	1.1	*
4	jsr166	1.2	* Copyright 2005 Sun Microsystems, Inc. All rights reserved.
5	dl	1.1	* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6			*/
7
8			package java.util;
9
10			/**
11	jsr166	1.3	* The <code>Stack</code> class represents a last-in-first-out
12			* (LIFO) stack of objects. It extends class <tt>Vector</tt> with five
13			* operations that allow a vector to be treated as a stack. The usual
14	dl	1.1	* <tt>push</tt> and <tt>pop</tt> operations are provided, as well as a
15	jsr166	1.3	* method to <tt>peek</tt> at the top item on the stack, a method to test
16			* for whether the stack is <tt>empty</tt>, and a method to <tt>search</tt>
17	dl	1.1	* the stack for an item and discover how far it is from the top.
18			* <p>
19	jsr166	1.3	* When a stack is first created, it contains no items.
20	dl	1.1	*
21	jsr166	1.3	* <p>A more complete and consistent set of LIFO stack operations is
22			* provided by the {@link Deque} interface and its implementations, which
23	dl	1.1	* should be used in preference to this class. For example:
24	jsr166	1.3	* <pre> {@code
25			* Deque<Integer> stack = new ArrayDeque<Integer>();}</pre>
26	dl	1.1	*
27			* @author Jonathan Payne
28	jsr166	1.2	* @version %I%, %G%
29	dl	1.1	* @since JDK1.0
30			*/
31			public
32			class Stack<E> extends Vector<E> {
33			/**
34			* Creates an empty Stack.
35			*/
36			public Stack() {
37			}
38
39			/**
40	jsr166	1.3	* Pushes an item onto the top of this stack. This has exactly
41	dl	1.1	* the same effect as:
42			* <blockquote><pre>
43			* addElement(item)</pre></blockquote>
44			*
45			* @param item the item to be pushed onto this stack.
46			* @return the <code>item</code> argument.
47			* @see java.util.Vector#addElement
48			*/
49			public E push(E item) {
50			addElement(item);
51
52			return item;
53			}
54
55			/**
56	jsr166	1.3	* Removes the object at the top of this stack and returns that
57			* object as the value of this function.
58	dl	1.1	*
59	jsr166	1.3	* @return The object at the top of this stack (the last item
60	dl	1.1	* of the <tt>Vector</tt> object).
61			* @exception EmptyStackException if this stack is empty.
62			*/
63			public synchronized E pop() {
64			E obj;
65			int len = size();
66
67			obj = peek();
68			removeElementAt(len - 1);
69
70			return obj;
71			}
72
73			/**
74	jsr166	1.3	* Looks at the object at the top of this stack without removing it
75			* from the stack.
76	dl	1.1	*
77	jsr166	1.3	* @return the object at the top of this stack (the last item
78			* of the <tt>Vector</tt> object).
79	dl	1.1	* @exception EmptyStackException if this stack is empty.
80			*/
81			public synchronized E peek() {
82			int len = size();
83
84			if (len == 0)
85			throw new EmptyStackException();
86			return elementAt(len - 1);
87			}
88
89			/**
90			* Tests if this stack is empty.
91			*
92	jsr166	1.3	* @return <code>true</code> if and only if this stack contains
93	dl	1.1	* no items; <code>false</code> otherwise.
94			*/
95			public boolean empty() {
96			return size() == 0;
97			}
98
99			/**
100	jsr166	1.3	* Returns the 1-based position where an object is on this stack.
101			* If the object <tt>o</tt> occurs as an item in this stack, this
102			* method returns the distance from the top of the stack of the
103			* occurrence nearest the top of the stack; the topmost item on the
104			* stack is considered to be at distance <tt>1</tt>. The <tt>equals</tt>
105			* method is used to compare <tt>o</tt> to the
106	dl	1.1	* items in this stack.
107			*
108			* @param o the desired object.
109	jsr166	1.3	* @return the 1-based position from the top of the stack where
110	dl	1.1	* the object is located; the return value <code>-1</code>
111			* indicates that the object is not on the stack.
112			*/
113			public synchronized int search(Object o) {
114			int i = lastIndexOf(o);
115
116			if (i >= 0) {
117			return size() - i;
118			}
119			return -1;
120			}
121
122			/** use serialVersionUID from JDK 1.0.2 for interoperability */
123			private static final long serialVersionUID = 1224463164541339165L;
124			}