KABA is an innovative system for refactoring Java class hierarchies. It uses the Snelting/Tip algorithm [13] in order to determine a behavior-preserving refactoring which is optimal with respect to a given set of client programs. KABA can be based on dynamic as well as static program analysis. The static variant will preserve program behavior for all possible input values; the dynamic version guarantees preservation of behavior for all runs in a given test suite. KABA offers automatic refactoring as well as manual refactoring using a dedicated editor.In this contribution, we recapitulate the Snelting/Tip algorithm, present the new dynamic version, and explain new extensions which allow to handle full Java. We then present five case studies which discuss the KABA refactoring proposals for programs such as javac and antlr. KABA proved that javac does not need refactoring, but generated semantics-based refactoring proposals for antlr.