In our batch jobs for data import we had many similar classes for holding the data being imported. Technically they are all different, with different fields, yet conceptually they are all same. I find this conceptual duplication discomforting and have written a single, more generic, class to replace them all.
The refactoring has been inspired by Clojure and its preference of few generic structures such as maps with many functions over the OO way of many case-specific data structures (i.e. classes), as explained for example in this interview of Rich Hickey, starting with “OO can seriously thwart reuse”.
The original code:
The refactored code, where all the LogEntry implementations have been replaced by MapLogEntry:
Improvements We have replaced about 15 classes with one, made it possible to change the way data are transformed into a tab-separated string at a single place (DRY), and provided a nice, fluent API whose use looks quite similarly at each place. The new MapLogEntry is also much more testing-friendly (it would be a nightmare to modify all the existing classes to support what M.L.E. does).
Objections Somebody might consider a number of primitive POJO classes simpler than one generic class. The one generic class is certainly more complex than a primitive data structure but in total the solution is less complex because there is fewer pieces and the single piece is used in the same way everywhere so the resulting cognitive load is smaller. The former code is more “easy” to understand while the latter is, all in all, more “simple.”
Principles DRY
