private double doubleValue ( double left , double right ) { switch ( operator ) { case ' ' : return left + right ; case ' ' : return left - right ; case ' ' : return left * right ; case ' ' : return left / right ; default : throw createException ( "Not supported Oprator '" + operator + "' for Expression '" + toString ( ) + ' ' ) ; } }
Calculate the number value of two operands if possible .