public class OurStack4 {

    char[] letters;
    int top;

    public OurStack4 ()
    {
	letters = new char [100];
	top = 0;
    }

    public void push (char ch)
    {
	letters[top] = ch;
	top ++;
    }


    public char pop ()
        throws OurStackException
    {
	if (top > 0) {
	    top --;
	    return letters[top];
	}
	else {
	    // Error: throw an exception
            throw new OurStackException ();
	    // Don't need this: return '@';
	}
    }


    public boolean isEmpty ()
    {
	if (top == 0) {
	    return true;
	}
	else {
	    return false;
	}
	// Alt: return (top==0? true: false);
    }

}