This estimates the number of different callables (= methods or constructors) that can be executed when a callable is invoked on this type.

In ideal world, we would compute a precise static approximation of the dynamic call graph, and then take the number of reachable callables from each callable. However, there are two problems with such an approach. First, it is very expensive to compute such an approximation. Second, the approximation is likely to be crude, even when using these expensive algorithms.

For that reason, Chidamber and Kemerer suggested in their seminal 1994 article that one just counts the number of calls within the classes callables. Indeed Spinellis's ckjm tool does precisely that, and we follow its lead.

Pre-packaged Query

Name of query = "Semmle/Metrics/Types/RefTypes that have high response"

Reports types that have a response higher than 100.

from MetricRefType t, int d
where t.fromSource() and d = t.getResponse() and d > 100
select t, d order by d desc

.QL Source of Metric

This metric is defined in MetricRefType. It reads:

int getResponse() {
  result = sum(Callable c | c.getDeclaringType()=this | count(c.getACall()))
} 

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.

David Grove, Greg DeFouw, Jeffrey Dean, Craig Chambers. Call Graph Construction in Object-Oriented Languages . In: Proceedings of OOPSLA '97, pages 108-124, 1997.

Diomides D. Spinnelis. Code Quality: The Open Source Perspective. Addison-Wesley 2007.

Diomides D. Spinnelis. ckjm - Chidamber and Kemerer Java Metrics. (implementation of CK metrics), 2006.