public JulianDate add(int units,int amount){
  JulianDate date=null;
synchronized (gc) {
    gc.setTime(getJavaDate());
    gc.add(units,amount);
    date=new JulianDate(gc.getTime());
  }
  return date;
}

public JulianDate add ( int units , int amount ) { JulianDate date = null ; synchronized ( gc ) { gc . setTime ( getJavaDate ( ) ) ; gc . add ( units , amount ) ; date = new JulianDate ( gc . getTime ( ) ) ; } return date ; }
add the given number of period units to this date .
