Multi-format calculator - Software Development Case Studies in Java - page 147

base operand_1

<< abstract >>
Base

Calculator Rational

operand_2

format

<< abstract >>
Format

DecimalBase BinaryBase HexBase

FractionalFormat FixedPointFormat FloatingPointFormat

Figure 6.8 Calculator with format and base classes

: Base

3 : parse()

1 : addOperand()

2 : parse()

command :
Command

calc calc : Calculator format : Format

4 : new

: Rational

Figure 6.9 Collaboration for adding a new operand

new operand (1). The Calculator invokes the parse() method on the Format
object and passes the Base object as a parameter (2). Thus Format is able to
call the parse() method on the base to convert the number using the given
number base (3). Finally the method parse() of Format creates a new Rational
object.

6.5.3 Implementation

Class Base implements the generic concept of number base, it provides two
essential methods: parse() converts a string representation of a number into
a double, toString() does the opposite. The former is based on Equation 6.1,
while the latter uses Equation 6.2 and Equation 6.4. These methods can be
customized using two parameters: the base and the digits; they are stored in
the homonymous attributes and are initialized through the constructor.