public void addOperand(ISpacePredicate operand){
  if (_operandsList == null)   _operandsList=new ArrayList<ISpacePredicate>();
  _operandsList.add(operand);
}

public void addOperand ( ISpacePredicate operand ) { if ( _operandsList == null ) _operandsList = new ArrayList < ISpacePredicate > ( ) ; _operandsList . add ( operand ) ; }
adds an operand at the end of the current operands list .
