The Law of Demeter

Don't talk to strangers.

The Law of Demeter, also known as "The Principle of Least Knowledge" is a principle for software design, particularly relevant in object orientated languages.

It states that a unit of software should talk only to its immediate collaborators. An object A with a reference to object B can call its methods, but if B has a reference to object C, A should not call Cs methods. So, if C has a doThing() method, A should not invoke it directly; B.getC().doThis().

Following this principal limits the scope of changes, making them easier and safer in future.