stack.java

来自「《移动Agent技术》一书的所有章节源代码。」· Java 代码 · 共 114 行

/*
 * @(#)Stack.java	1.16 97/01/28
 * 
 * Copyright (c) 1995, 1996 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the confidential and proprietary information of Sun
 * Microsystems, Inc. ("Confidential Information").  You shall not
 * disclose such Confidential Information and shall use it only in
 * accordance with the terms of the license agreement you entered into
 * with Sun.
 * 
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
 * SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
 * THIS SOFTWARE OR ITS DERIVATIVES.
 * 
 * CopyrightVersion 1.1_beta
 * 
 */

package java.util;

/**
 * The <code>Stack</code> class represents a last-in-first-out 
 * (LIFO) stack of objects. 
 *
 * @author  Jonathan Payne
 * @version 1.16, 01/28/97
 * @since   JDK1.0
 */
public
class Stack extends Vector {
    /**
     * Pushes an item onto the top of this stack. 
     *
     * @param   item   the item to be pushed onto this stack.
     * @return  the <code>item</code> argument.
     * @since   JDK1.0
     */
    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.
     * @exception  EmptyStackException  if this stack is empty.
     * @since      JDK1.0
     */
    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. 
     * @exception  EmptyStackException  if this stack is empty.
     * @since      JDK1.0
     */
    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 this stack is empty;
     *          <code>false</code> otherwise.
     * @since   JDK1.0
     */
    public boolean empty() {
	return size() == 0;
    }

    /**
     * Returns where an object is on this stack. 
     *
     * @param   o   the desired object.
     * @return  the distance 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.
     * @since   JDK1.0
     */
    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;
}