/* * @(#)Stack.java	1.26 03/01/23 * * Copyright 2003 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.  * * @author  Jonathan Payne * @version 1.26, 01/23/03 * @since   JDK1.0 */publicclass Stack extends Vector {    /**     * 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 Object push(Object 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 Object pop() {	Object	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 Object 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;}