Java program codes: stack demo in java

import java.util.*;

public class StackDemo{
public static void main(String[] args) {
Stack stack=new Stack();
stack.push(new Integer(10));
stack.push("a");
System.out.println("The contents of Stack is" + stack);
System.out.println("The size of an Stack is" + stack.size());
System.out.println("The number poped out is" + stack.pop());
System.out.println("The number poped out is " + stack.pop());
//System.out.println("The number poped out is" + stack.pop());
System.out.println("The contents of stack is" + stack);
System.out.println("The size of an stack is" + stack.size());
}
}