Are There Metrics For Cohesion And Coupling?

Question

Is there a metric analogous to the McCabe Complexity measure to measure how cohesive a routine is and also how loosely (or tightly) coupled the routine is to other code in the same code base?

Answer 1

I think the metric you are looking for is LCOM4, although it applies more to classes.

Sonar explains it nicely here:

...metric : LCOM4 (Lack Of Cohesion Methods) to measure how cohesive classes are. Interpreting this metric is pretty simple as value 1 means that a class has only one responsibility (good) and value X means that a class has probably X responsibilities (bad) and should be refactored/split.

There is not any magic here, only common sense. Let’s take a simple example with class Driver. This class has two fields : Car and Brain, and five methods : drive(), goTo(), stop(), getAngry() and drinkCoffee(). Here is the dependency graph between those components. There are three blocks of related components, so LCOM4 = 3, so the class seems to have three different responsibilities and breaks the Single Responsibility Principle.

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It's a great tool, if you can use it. :)

Answer 2

• Afferent coupling: Number of responsibilities
• Efferent coupling: Number of dependencies
• Instability: Ratio of efferent coupling to total coupling (Afferent + Efferent).

Instability is supported in various code metric tools.