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 * Copyright (c) 1994, 2010, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package java.util;

/**
 * The {@code Stack} class represents a last-in-first-out
 * (LIFO) stack of objects. It extends class {@code Vector} with five
 * operations that allow a vector to be treated as a stack. The usual
 * {@code push} and {@code pop} operations are provided, as well as a
 * method to {@code peek} at the top item on the stack, a method to test
 * for whether the stack is {@code empty}, and a method to {@code search}
 * 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
 * @since 1.0
 */
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} 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 {@code Vector} object).
 * @throws 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 {@code Vector} object).
 * @throws 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} if and only if this stack contains
 * no items; {@code false} otherwise.
 */
 public boolean empty() {
 return size() == 0;
 }

 /**
 * Returns the 1-based position where an object is on this stack.
 * If the object {@code o} 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 {@code 1}. The {@code equals}
 * method is used to compare {@code o} 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}
 * 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;
}