Software Engineering for Students A Programming Approach

82 Chapter 6 ■ Modularity
■ input transaction
■ open valve
■ obtain date
As with the ideas of coupling, if we find that the methods in our software exhibit
poor cohesion, the concepts of cohesion do not provide us with a method for improving
our structure – they merely tell us how poor our structure is. Another problem with
the classification scheme is that it is sometimes very difficult to identify which type of
cohesion is present.
SELF-TEST QUESTION
6.2 A library method draws a line from one set of coordinates to another.
What type of cohesion does it exhibit?
6.10 ● Object-oriented programming
In this form of programming, methods and data that are strongly related are grouped
together into an object. This matches exactly the ideas of information hiding and encapsulation
discussed above. The items within an object are strongly coupled and the object
as a whole possesses high cohesion. A well-designed object presents a few simple interfaces
to its clients. The interfaces are those public methods that are declared to be accessible outside
of the object. Thus a well-designed object displays loose coupling with other objects –
method calls with pure data parameters to methods with functional cohesion. It is possible
to code an object that allows clients direct access to its variables, but this is regarded as
poor practice and is heavily discouraged because it is essentially making data global.
Object-oriented languages encourage the programmer to describe classes rather than
individual objects. For example, here is the description, in Java, of a graphical object, a
ball, which has x and y screen coordinates:
class Ball {
protected int x, y;
private int radius;
public void setRadius(int newRadius) {
radius = newRadius;
}
public void setX(int newX) {
x = newX;
}
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