Systems

The startup process/logic should be separate from the runtime logic.

• One solution is to do all construction in main or modules called by main, then run the rest of the system assuming everything in main has initialized correctly.

For objects that will be created while the program is already initialized and running, we can use an abstract factory

• E.g. when the program starts, the factory is initialized, and then while the program is running the factory is responsible for creating new objects of that type.

Dependency Injection - an object should not be responsible for creating its required dependencies - instead they should be injected into the object by an outside authority.

• I.E. the class has setters or constructor arguments that pass in its dependencies; the class itself does nothing with their instantiation.

Tightly coupled dependencies/logic make it hard to extend/add to the code since you have to work around the coupled dependencies.

"An optimal system architecture consists of modularized domains of concern, each of which is implemented with Plain Old Java (or other) Objects. The different domains are integrated together with minimally invasive Aspects or Aspect-like tools. This architecture can be test-driven, just like the code."

Obviously the book is Java oriented, but the idea is there.