A more complex example to practice the Mikado Method
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This repository contains messy code for practicing the Mikado Method, refactorings and restructurings, clean code and object-oriented design.


The project has a Space class that is the main class. The main() method takes no parameters.

The Space class has two static boolean members that control behavior, IS_BOUNCING_BALLS and IS_BREAKOUT.

If IS_BOUNCING_BALLS is false, the application is a simulation of a solar system, not that different from ours. The value of IS_BREAKOUT doesn't matter.

If IS_BOUNCING_BALLS is true, the application shows a box of bouncing balls. If IS_BREAKOUT is true, the balls can exit through the lower side of the box. If IS_BREAKOUT is false, the balls just keep bouncing in the box.

There are also some tests available. They don't cover all the code, just as in real life. ;-)


Each of the exercises can start from a fresh pull of the code. They can also start from the previous (working) state as the exercises are completed.

Easy level


The PhysicalObject is to be used in another project. However, the entire Space class must NOT be shared. Your task is to extract the PhysicalObject to a new project.


Enable reuse of PhysicalObject

Intermediate level


The solar system and bouncing balls applications are to be sold in separate delivery packages. Due to legal issues, the solar system may not contain any bouncing balls logic and vice versa.


Two separate, minimal, deliverables for bouncing balls and solar system.

Difficult level


The application is a huge success, and will be ported to a limited device without Swing/AWT support. The exact API of the new graphics support is not ready, but to be first on the market when it arrives, you need to start separating presentation logic from domain ASAP.


The domain logic is compilable without Swing/AWT dependencies. When Swing/AWT + any bridging code is available, the application should be runnable.