Unit 16: Debugging, Refactoring, Packages, and Project Structure

You now have enough Java to create problems that syntax drills cannot solve.

This unit pulls the course together around three engineering behaviors:

1. locate the first meaningful divergence between expected and observed state;
2. improve internal structure while regression tests protect required behavior;
3. move from compact/single-source learning programs into explicit classes, packages, and multi-file project boundaries when scale requires them.

Checkpoint 5 is a tested refactor. The program must become easier to reason about without losing behavior.