The efferent coupling of a package p is the number of types inside p that directly depends on types outside p.

A high efferent coupling may be an indication that perhaps this package could be merged with others. However, the main function of efferent coupling is to define the stability metric.

For a detailed discussion of the notion of dependency between types, please refer to Afferent Coupling of a Type.

Pre-packaged Query

Query name = "Semmle/Metrics/Packages/Coupling/Packages that have high efferent coupling"

Reports packages that have efferent coupling greater than 20, in descending order, as a bar chart.

from MetricPackage p, int c
where p.fromSource() and c = p.getEfferentCoupling() and c > 20
select p, c order by c desc

.QL Source of Metric

This metric is defined in MetricPackage. Its definition reads:

    int getEfferentCoupling() {
      result = count(RefType t |
                       t.getPackage() = this
                       and
                       exists(RefType s |
                              s.getPackage() != this
                              and
                              depends(t,s)))
    }

References

Robert C. Martin. OO Design Quality Metrics. October 24, 1994.

Robert C. Martin. Agile Software Development, Principles, Patterns and Practices. Addison Wesley, 2002.

Andrew Glover . In Pursuit of Code Quality: Code Quality for Software Architects. April 2006.

Jack Shirazi and Kirk Pepperdine. Eye on performance: Determining the riskiness of change. July 2004.