8. The Single-Responsibility Principle (SRP)
© Jennifer M. Kohnke
None but Buddha himself must take the responsibility of giving out occult secrets . . .
—E. Cobham Brewer 1810–1897, Dictionary of Phrase and Fable (1898)
This principle was described in the work of Tom DeMarco1 and Meilir Page-Jones.2 They called it cohesion, which they defined as the functional relatedness of the elements of a module. In this chapter, we modify that meaning a bit and relate cohesion to the forces that cause a module, or a class, to change.
The Single-Responsibility Principle
A class should have only one reason to change.
Consider the bowling game from Chapter ...