Dependency Metrics on Packages
- Efferent (outward) couplings measure
the number of packages the package we are examining depends on.
- Afferent (inward) couplings measure
the number of other packages that depend on the package we are examining.
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Stable Dependencies Principle
dependencies in our packages should follow the direction of stability:
less stable packages should depend on more stable ones.

An unstable package in Tomcat
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A stable package in the Eclipse distribution