@Pattern(name="Facade", scope=Object, purpose=Structural, participants={"Facade","SubsystemClass"})

Package dk.rode.thesis.facade

Implementations and examples of the Facade design pattern [Gamma95, p.185].

See:
Description

Class Summary

AckermannSequence	An Ackermann sequence calculates the next value of the Ackermann function, v = A(m, n), each time AckermannSequence.next() is invoked, using a fixed value for m and thus increasing n, either indefinitely, or until a maximum value has been reached.
FibonacciSequence	A Fibonacci sequence represents an integer sequence, where each number delivered by FibonacciSequence.next() is the sum of the two preceding numbers, except one which is the initial value: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, ..
Main	Facade tests.
MathFacade	A math facade is a small math library that represents an-easy-to-use high-level interface for complex mathematical functions.
RandomSequence	A random sequence returns a pseudo integer random number with each call to RandomSequence.next() between [0, maximum], where maximum is supplied at construction time.
UnboundedRandomSequence	An unbounded random sequence returns a pseudo integer random number with each call to UnboundedRandomSequence.next() with no upper bound.

Package dk.rode.thesis.facade Description

Implementations and examples of the Facade design pattern [Gamma95, p.185].

Intent:

Provide a unified interface to a set of interfaces in a sub—system. Facade defines a higher—level interface that makes the sub—system easier to use.

Here, the Facade participant is represented by the MathFacade class. It supplies an an-easy-to-use high-level interface to complex mathematical functions that internally are implemented using various Sequence types.

Specific SubsystemClass participants defined in this package are AckermannSequence, FibonacciSequence, RandomSequence, and UnboundedRandomSequence, while various classes from other packages are also used to represent sub-system classes, for example SequenceIterator and ReversiblePrimeSequence.

UML Class Diagram:

Implementation notes:
The small examples used throughout this thesis does not really justify use of Facade; they are simply not complex enough. Still, this Facade implementation address several issues discussed by Gamma et al. [Gamma95, p.185-193]:

• The mathematical functions implemented with Sequence types are too verbose and tedious to be implemented by any client, and hence this facade help provide the desired functionality, shielding clients from the gory details.

• The facade shield the client from knowing about specific sub-system classes, i.e. sequences. Some sequences are declared package private, others not. This illustrate the use of private and public sub-system classes as discussed by Gamma et al. [Gamma95, p.188]

• The facade implementation use package private access to ensure certain sub-system classes are off-limit from clients. An example is the AckermannSequence class.

• The facade is implemented as a Singleton.

Author:

Gunni Rode / rode.dk