public abstract class main3 {
    public static void main(String [] args) {
        StackI<String> s=new Stack<String>();
        StackI<String> t=new stack<String>();
        s.push("foo");  System.out.println("s="+s);
        s.push("bar");  System.out.println("s="+s);
        t.push("boing");  System.out.println("t="+t);
        s.push("flip");  System.out.println("s="+s);
        System.out.println(s.pop());  System.out.println("s="+s);
        s.push("flop");  System.out.println("s="+s);
        System.out.println(s.pop());  System.out.println("s="+s);
        System.out.println(t.pop());  System.out.println("t="+t);
        System.out.println(s.pop());  System.out.println("s="+s);
        System.out.println(s.pop());  System.out.println("s="+s);
    }
}