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Top 50 Design Patterns (Gang of Four) Interview Questions & Answers (2026)

50 Questions 20 Beginner 20 Intermediate 10 Advanced

About Design Patterns (Gang of Four)

Top 50 Design Patterns interview questions covering creational, structural, and behavioral patterns from the Gang of Four book. Companies hiring for Design Patterns (Gang of Four) roles test this knowledge at every stage — from first-round screens that check the basics to final-round conversations about real-world trade-offs.

What to Expect in a Design Patterns (Gang of Four) Interview

Expect a mix of conceptual and practical Design Patterns (Gang of Four) questions: clear definitions and core-concept checks for junior roles, hands-on scenario questions for mid-level roles, and architecture or trade-off discussions for senior roles. Interviewers usually move from foundational topics toward the kind of problems you'd actually face on the job.

How to Use This Guide

Work through the Design Patterns (Gang of Four) questions in order — Beginner, then Intermediate, then Advanced — so each concept builds on the last. Every question has its own page; bookmark the ones that trip you up and revisit them the day before your interview.

Curated by Tech Baithak Editorial Team · Last updated: May 2026

Beginner 20 questions

Core concepts every Design Patterns (Gang of Four) developer must know.

01 What is the Singleton design pattern? 02 What is the Factory Method design pattern? 03 What is the Abstract Factory design pattern? 04 What is the Builder design pattern? 05 What is the Prototype design pattern? 06 What is the Adapter design pattern? 07 What is the Bridge design pattern? 08 What is the Composite design pattern? 09 What is the Decorator design pattern? 10 What is the Facade design pattern? 11 What is the Flyweight design pattern? 12 What is the Proxy design pattern? 13 What is the Chain of Responsibility design pattern? 14 What is the Command design pattern? 15 What is the Iterator design pattern? 16 What is the Mediator design pattern? 17 What is the Memento design pattern? 18 What is the Observer design pattern? 19 What is the State design pattern? 20 What is the Strategy design pattern?

Intermediate 20 questions

Practical knowledge for developers with hands-on experience.

01 What is the Template Method design pattern? 02 What is the Visitor design pattern? 03 What is the difference between Factory Method and Abstract Factory? 04 When should you NOT use design patterns? 05 How are the Gang of Four patterns categorized? 06 How are GoF patterns used in real-world frameworks? 07 How can you combine the Decorator and Strategy patterns? 08 What is the difference between Decorator and Composite? 09 What is the difference between Observer and Mediator? 10 What is the difference between Strategy and Template Method? 11 What are the different types of Proxy? 12 How does the Command pattern support undo/redo? 13 What is the difference between Bridge and Adapter? 14 How does the Facade pattern differ from Mediator? 15 What are the internals of the Iterator pattern? 16 What are practical use cases for the Memento pattern? 17 What is the difference between Chain of Responsibility and Decorator? 18 How are GoF patterns used in Java and Python? 19 What is the Interpreter design pattern? 20 How does the Observer pattern relate to event-driven programming?

Advanced 10 questions

Deep expertise questions for senior and lead roles.

01 How do you implement a thread-safe Singleton using double-checked locking? 02 How do the SOLID principles relate to GoF patterns? 03 What is the difference between GoF anti-patterns and the patterns themselves? 04 How are GoF patterns used in modern frameworks like Spring and Django? 05 What criteria should guide pattern selection? 06 How do GoF patterns apply in functional programming? 07 What is the difference between dependency injection and the Service Locator pattern? 08 How does the Observer pattern scale in event-driven and distributed systems? 09 How can you use the Composite and Visitor patterns together? 10 How do GoF patterns apply to distributed systems design?

Back to All Topics 50 questions total