Ugly code: The Law of Demeter

I’ve recently come to a heuristic called the Law of Demeter (LoD) or Principle of Least Knowledge that says a module should not know about the innards of the objects it manipulates. More precisely, the method of a particular class should call:

• other methods of the same class
• objects created by the method itself
• objects passed as arguments to the method
• objects held in an instance variable of the same class

And that”s all!

So the following code appears to violate the Law:

String output = obj.getContext().getOptions().getDir().getPath();

It’s easy to forget something around such a structure. This one can solve the issue:

String output = obj.getPathFromContext();

Related posts:

1. Clean code
2. Collision detection in practice
3. Testing java with JUnit
4. Intro C++
5. PMD XPath: creating custom rules