This metric simply measures the number of immediate subtypes of a reference type in the inheritance hierarchy.

This number is an indicator of the number of responsibilities of a class, and of its importance in the design of the system as a whole. Rosenberg and Hyatt recommend that classes with a large number of children be thoroughly tested.

Pre-packaged Query

Name of Query = "Semmle/Metrics/Types/Reftypes with many children"

Reports reference types in the source that have more than more than five immediate descendants, in decreasing order, as a bar chart.

from MetricRefType t, int n
where t.fromSource() and
      n = t.getNumberOfChildren() and
      n > 5
select t,n order by n desc

.QL Source of Metric

This metric is defined in the class MetricRefType. Its definition reads:

int getNumberOfChildren() {
   result = count(this.getASubtype())
}

References

Shyam R. Chidamber and Chris F. Kemerer. A Metrics Suite for Object Oriented Design . IEEE Transactions on Software Engineering, 20(6), pages 476-493, June 1994.

Linda H. Rosenberg and Lawrence E. Hyatt. Software Quality Metrics for Object-Oriented Environments NASA Software Assurance Technology Center, April 1997.