Method isValid

ch2/YoilTellerMVC5.java:52–54

(MyDate date)

    }

    private boolean isValid(MyDate date) {
    	return isValid(date.getYear(), date.getMonth(), date.getDay());
    }
    
    private boolean isValid(int year, int month, int day) {    
    	if(year==-1 || month==-1 || day==-1)