public abstract class main4 {
    public static void main(String [] args) {
        StackI<Object> s=new Stack<Object>();
        StackI<Double> t=new stack<Double>();
        s.push(2);  System.out.println("s="+s);
        s.push("foo");  System.out.println("s="+s);
        t.push(7.34);  System.out.println("t="+t);
        s.push(null);  System.out.println("s="+s);
        System.out.println(s.pop());  System.out.println("s="+s);
        s.push(-12.3);  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);
    }
}