Software Architecture & Engineering

What the Law of Demeter is, why it is needed, and how to reduce coupling by limiting what objects depend on and expose.

What the composition reuse principle is, why it is needed, and how composition or aggregation can be preferred over inheritance for code reuse.

What object-oriented design principles are, why they are needed, and the main principles covered by these notes.

What design patterns are and the three main categories: creational, structural, and behavioral.

A class has one and only one instance, with Java and Go implementations including eager, lazy, DCL, static-inner-class, enum, mutex, and sync.Once approaches.

The proxy pattern adds functionality around an existing class or function without changing the original code, with static, dynamic, AOP, Go, and cache-proxy examples.

The template-method pattern applies when the overall algorithm steps are fixed while some parts vary, with Java and Go implementations and a combined template/factory/strategy example.

The factory-method pattern uses multiple factory classes and delays concrete product creation to subclasses.

The state pattern selects different processing logic according to the current state, with Java and Go examples.

The builder pattern constructs a complex object from many smaller parts; the builder creates the parts and the director assembles them.