Implement and compare key design patterns
Implement Core GoF Patterns in Java and Discuss Trade-offs
Context
You are designing a small Java library and want to demonstrate three classic GoF design patterns with concise examples. You should:
-
Implement a thread-safe, lazy Singleton.
-
Implement the Factory Method pattern.
-
Implement the Strategy pattern and a simple client that uses it.
-
Compare these patterns in terms of trade-offs, extensibility, and testability.
-
Refactor one example to reduce coupling and enable dependency injection (constructor injection is fine).
Keep code snippets small and focused on illustrating the pattern rather than full application logic.
Constraints & Assumptions
-
Preserve the scope, facts, inputs, and requested outputs from the prompt above.
-
If the prompt leaves a detail unspecified, state a reasonable assumption before relying on it.
-
Keep the answer interview-ready: concise enough to present, but concrete enough to implement or evaluate.
Clarifying Questions to Ask
-
Clarify users, core use cases, read/write patterns, scale, latency, availability, and data retention.
-
State explicit assumptions before making sizing or architecture decisions.
-
Prioritize the functional path first, then address reliability, security, observability, and rollout.
What a Strong Answer Covers
-
A scoped requirements summary with concrete non-goals and success metrics.
-
API, data model, architecture, consistency, capacity, and operations.
-
Reasoned trade-offs among simple and scalable designs, including bottlenecks and failure modes.
-
A validation, monitoring, migration, and launch plan appropriate for the risk level.
Follow-up Questions
-
What breaks first at 10x traffic or data volume?
-
How would you degrade gracefully during dependency failures?
-
What metrics and alerts would prove the design is healthy after launch?