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package java.util;


The Stack class represents a last-in-first-out (LIFO) stack of objects. It extends class Vector with five operations that allow a vector to be treated as a stack. The usual push and pop operations are provided, as well as a method to peek at the top item on the stack, a method to test for whether the stack is empty, and a method to search the stack for an item and discover how far it is from the top. 

When a stack is first created, it contains no items.

A more complete and consistent set of LIFO stack operations is provided by the Deque interface and its implementations, which should be used in preference to this class. For example: 
 
  Deque<Integer> stack = new ArrayDeque<Integer>();


Author: Jonathan Payne
Since:  1.0
/**
 * 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.

/**
     * Creates an empty Stack.
     */
    public Stack() {
    }

    
Pushes an item onto the top of this stack. This has exactly
the same effect as:

addElement(item)


Params:
  • item –   the item to be pushed onto this stack.
See Also:
Returns: the item argument.
/**
     * 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.

Throws:
Returns: The object at the top of this stack (the last item of the Vector object).
/**
     * 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.

Throws:
Returns: the object at the top of this stack (the last item of the Vector object).
/**
     * 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.

Returns: true if and only if this stack contains no items; false otherwise.
/**
     * 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 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 1. The equals method is used to compare o to the items in this stack. 
Params:
  • o –   the desired object.
Returns: the 1-based position from the top of the stack where the object is located; the return value -1 indicates that the object is not on the stack.
/**
     * 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 
/** use serialVersionUID from JDK 1.0.2 for interoperability */
    private static final long serialVersionUID = 1224463164541339165L;
}