private void checkType(BtrpOperand e) {
        if (!(e instanceof BtrpNumber)) {
            throw new UnsupportedOperationException(e + " must be a '" + prettyType() + "' instead of a '" + e.prettyType() + "'");
        }
    }
private void checkType ( BtrpOperand e ) { if ( ! ( e instanceof BtrpNumber ) ) { throw new UnsupportedOperationException ( e + " must be a '" + prettyType ( ) + "' instead of a '" + e . prettyType ( ) + "'" ) ; } }
Check the operand is a number. If not, throws a {@link UnsupportedOperationException} exception.

@param e the operand to check