public abstract class intStack { // abstract ADT
    public abstract boolean empty ();
    public abstract void push (int i);
    public abstract int pop ();
    public void print () {
	int i;

	if (this.empty ()) {
	    Out.println ("The end of stack.");
	} else {
	    i = this.pop ();
	    Out.println (i + ""); this.print ();
	    this.push (i);
	}
    }
}