Coupling Between Object Classes

Number of classes to which a class is coupled.

Two classes are coupled when methods declared in one class use methods or instance variables defined by the other class. The uses relationship can go either way: both uses and used-by relationships are taken into account, but only once.

Multiple accesses to the same class are counted as one access. Only method calls and variable references are counted.

High CBO is undesirable. Excessive coupling between object classes is detrimental to modular design and prevents reuse. The more independent a class is, the easier it is to reuse it in another application. In order to improve modularity and promote encapsulation, inter-object class couples should be kept to a minimum. The larger the number of couples, the higher the sensitivity to changes in other parts of the design, and therefore maintenance is more difficult. A high coupling has been found to indicate fault-proneness.

A recommended CBO is 12 or less.

Additional resources:

• Chidamber-Kemerer metrics paper

Config example

dart_code_metrics:
  ...
  metrics:
    ...
    coupling-between-object-classes: 12
    ...