What does $$ and means in java stacktrace?

Question

Many times I get stacktraces like this one (please see the arrow for the confusing line):

org.springframework.dao.DataIntegrityViolationException: could not exec         


        

Answer 1

$ is an allowed character in class names.

The name SimpleDetectorPersistenceService$$EnhancerBySpringCGLIB$$66303639 hints that it is a class which was dynamically generated at runtime by Spring framework using CGLIB.

They use $$ and a numeric offset to make this class name unique to avoid conflicts with existing classes.

The string () in the stracktrace too was generated by CGLIB:
When CGLIB creates a class at runtime it uses as placeholder for the name of the source file. The stacktrace then simply prints this string instead of the real source file and line number.