public class Calculator {
    public int add(int x, int y) { return x+y; }
    public int mult(int x, int y) { return x*y; }

    public static void main(String[] args) {
	Calculator calc = new Calculator();
	assertEqual(calc.add(3,4),8,"add(3,4)");
	if ( calc.add(0,4)!=4 ) { System.err.println("error: add(0,4)"); }

	if ( calc.mult(0,4)!=0 ) { System.err.println("error: mult(0,4)"); }
    }

    public static void assertEqual(int result, int expecting, String msg) {
	if ( result!=expecting ) {
	    System.err.println("failure: "+msg+"="+result+"; expecting="+expecting);
	}
    }

}