public void addDecorator(final OperatorDrawDecorator decorator){
  if (decorator == null) {
    throw new IllegalArgumentException("decorator must not be null!");
  }
  operatorDecorators.add(decorator);
}

public void addDecorator ( final OperatorDrawDecorator decorator ) { if ( decorator == null ) { throw new IllegalArgumentException ( "decorator must not be null!" ) ; } operatorDecorators . add ( decorator ) ; }
adds the given operator draw decorator . the decorator is called directly after the operator was drawn .
