What are the interview questions for an application developer?

Application developer interviews typically cover a broad spectrum of skills, from coding fundamentals and system architecture to domain-specific knowledge (e.g., mobile vs. web, frontend vs. backend). Below is a curated list of sample questions across various categories to help you prepare. To strengthen your fundamentals and receive comprehensive guidance, explore the recommended DesignGurus.io courses at the end.

1. Coding & Algorithmic Questions

1. Data Structures & Algorithms

   • Can you explain the difference between arrays and linked lists? What are their pros and cons for insertion, deletion, and random access?
   • Describe a scenario where a hash map is more suitable than a tree-based data structure.
   • How do you detect a cycle in a linked list? (Follow-up: how do you remove it?)

2. Algorithmic Patterns

   • Give an example of how you’d use the sliding window technique to solve a subarray-based problem.
   • What is the two-pointer approach, and when would you consider it?
   • Describe backtracking. Can you outline how it differs from brute force?

3. Optimization & Complexity

   • What is Big-O notation? Compare the complexities of bubble sort, merge sort, and quicksort.
   • How do you optimize a solution that’s running in O(n^2) time when you need faster performance?

Recommended Resource

• Grokking the Coding Interview: Patterns for Coding Questions
  This course delves deep into recurring coding patterns (sliding window, two pointers, BFS/DFS, etc.) to help you solve problems methodically.

2. System Design & Architecture Questions

1. Designing Scalable Apps

   • How would you design a messaging app (like WhatsApp) that needs to support millions of concurrent users?
   • What components are essential for ensuring high availability and scalability?

2. Microservices & APIs

   • What are microservices, and when would you use them over a monolithic architecture?
   • How do you design RESTful or GraphQL APIs? Which design principles do you follow (e.g., versioning, idempotency)?

3. Performance & Caching

   • How do you handle peak loads or sudden spikes in traffic (like flash sales or viral campaigns)?
   • How can caching improve performance, and what are the trade-offs (e.g., invalidation strategies, cache stampede)?

4. Database Selection

   • When would you choose a NoSQL database over a relational one?
   • Describe partitioning and sharding in databases. How does it help with scalability?

Recommended Resource

• Grokking the System Design Interview
  Explores distributed system concepts, load balancing, data partitioning, caching, and more—key topics in interviews for roles that demand large-scale or backend expertise.

3. Platform-Specific & Technical Deep Dive

Depending on the role (e.g., mobile developer, web developer, full stack engineer), expect questions tailored to that ecosystem.

1. Mobile (iOS/Android)

   • How does memory management differ between iOS and Android?
   • Explain the activity lifecycle in Android or the view controller lifecycle in iOS.
   • What are best practices for handling background tasks and push notifications?

2. Web & Frontend

   • Compare React, Angular, and Vue. What are the core principles of each?
   • How do you optimize performance for single-page applications (SPAs)?
   • What is the concept of virtual DOM, and how does it improve rendering performance?

3. Cross-Platform (React Native, Flutter, Xamarin)

   • How does Flutter achieve near-native performance?
   • How do React Native apps differ from pure native development, especially in terms of performance?
   • What is the role of “bridge” modules in cross-platform frameworks?

4. Best Practices & Code Quality

1. Design Patterns

   • How do you apply MVC, MVVM, or MVP patterns in your projects?
   • What is the Singleton pattern? Why can it be problematic, and how do you mitigate these issues?

2. Testing & QA

   • How do you approach unit testing vs. integration testing vs. end-to-end testing?
   • What tools or frameworks do you use for automated testing (e.g., Jest, Mocha, Espresso, XCTest)?

3. Security

   • How do you handle sensitive data (e.g., encryption at rest, secure key storage)?
   • What common security pitfalls do you watch out for (e.g., SQL injection, cross-site scripting, insecure direct object references)?

5. Behavioral & Team-Fit Questions

Employers also want to see how you approach collaboration, problem-solving under pressure, and continuous learning.

1. Collaboration & Communication

   • Describe a time you had to work with cross-functional teams (designers, QA, product managers). How did you ensure smooth communication?
   • Tell me about a time you had to resolve a technical disagreement within your team.

2. Problem-Solving & Learning

   • How do you stay updated with new technologies, frameworks, or best practices?
   • Describe a challenging bug you faced. What was your debugging process, and how did you resolve it?

3. Time Management & Prioritization

   • How do you handle tight deadlines or unexpected feature requests?
   • Give an example of a time you had to deliver an MVP first, then iterate.

Final Tips for Success

1. Combine Theory With Practice

   • While it’s important to know data structures, algorithms, and system design concepts, hands-on practice (e.g., small projects, open-source contributions) will strengthen your real-world understanding.

2. Mock Interviews

   • Participating in System Design Mock Interview or Coding Mock Interview sessions provides real-time feedback. You’ll hone your problem-solving speed, communication clarity, and confidence under pressure.

3. Showcase Strong Communication

   • Interviewers often look for clarity of thought and the ability to break down complex ideas. Use step-by-step explanations, articulate trade-offs, and be receptive to hints or corrections.

4. Stay Curious and Adaptable

   • Technology evolves rapidly. Demonstrating an eagerness to learn new tools, follow best practices, and implement feedback can set you apart—no matter the role.

By preparing across these categories—coding fundamentals, system design, platform-specific knowledge, best practices, and behavioral skills—you’ll enter your application developer interviews with a well-rounded approach. Combine this with courses like Grokking the Coding Interview and Grokking the System Design Interview to deepen your expertise and confidently tackle any challenge the interviewer presents. Good luck!