1. Why Patterns Matter in Interviews
Interviewers don't test design patterns for academic trivia; they look for standard vocabularies that produce extensible, decoupled code adhering to the Open/Closed Principle.
2. The Essential 7 Interview Patterns
1. Strategy Pattern: Pluggable algorithms (pricing models, payment methods, route finders).
2. Observer Pattern: Decoupled event pub/sub (notifying riders when a driver accepts).
3. State Pattern: Clean state transitions without 50 nested switch statements (order lifecycle, ATM states, elevator car motion).
4. Factory Method: Encapsulating object creation based on dynamic inputs.
5. Decorator Pattern: Adding responsibilities to objects dynamically without subclass explosion (pizza toppings, coffee extras, discount layers).
6. Chain of Responsibility: Passing requests along a handler pipeline (logging filters, approval workflows, currency note dispensers).
7. Adapter Pattern: Bridging incompatible legacy interfaces to new clean contracts.
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Written by HLDForge Architecture Team
Staff Systems Architect
The HLDForge Architecture Team publishes practical engineering guides, real-world case studies, and high-concurrency blueprints to help engineers build scalable and fault-tolerant software.