Low Level Design
How the Strategy pattern replaces complex if-else chains with interchangeable algorithm objects, keeping business logic clean and extensible.
How the Chain of Responsibility pattern decouples request senders from receivers, letting multiple objects get a chance to handle a request without the sender knowing which one will.
How the Null Object pattern replaces null references with do-nothing objects that implement the expected interface, removing defensive null checks throughout your codebase.
How the State pattern replaces complex state-based conditionals with dedicated state classes, making transitions explicit and individual states independently testable.
Build a type-safe, decoupled event system using the Observer pattern. Covers the classic GoF design, Java's built-in tools, and a modern generic implementation.