While there are workarounds -- for example, you could introduce a Factory class to generate transaction objects -- this adds complexity and could become a maintenance burden. Another approach could be ...

Abstract classes and interfaces in Java serve fundamentally different purposes. Learn the differences between these Java language elements and how to use them in your programs.

Packages can store classes and interfaces, as well as subpackages, which are packages nested within other packages. A package has a name, which must be a non-reserved identifier; for example, java.