The Hollywood Principle (Dont call us, we'll call you)

The Hollywood Principle (Don't call us, we'll call you)

Gives us a way to prevent dependency rot.
Dependency rot happens when you have high level components depending on low-level components depending on high-level components depending on side-way components depending on low-level components and so on.

With the Hollywood principle,  we allow low-level components to hook themselves into a system, but the high-level components determine when they are needed, and how. in other words, the high-level components give the low level components the "Don't call use, we'll call you" treatment.


The connection between the template design method and the Hollywood Principle is somewhat app-rant. Considering it is the abstract class (the higher level component) that calls the Subclasses implementations of its abstract methods.

Subclasses (low level components) never call abstract classes (high level components) without being called first.


Q: is a low level component disallowed from calling a method in a high-level component?

A Not really, IN, fact a low level component will often end up calling a member defined above in its inheritance hierarchy purely through inheritance. But we want to avoid creating explicit circular dependencies between the low-level component and the high-level ones.