n To determine if they are “equal” dates, we must compare their day, month, and year. public boolean equals (Object obj){   Require.condition(obj          instanceof Date);   Date d = (Date)obj;    return   this.year()==d.year() &&             this.month()==d.month() &&        this.day()==d.day(); } // instanceof returns true if the object is // an instance of // the class