Frequently Asked Interview Questions for SDE Role

Frequently Asked Interview Questions – SDE (Java/Spring Boot) Compensation Bracket: ₹20–25 LPA Role: Backend / Software Engineer 𝗖𝗼𝗿𝗲 𝗝𝗮𝘃𝗮 • Difference between HashMap, HashTable, and ConcurrentHashMap • How does Garbage Collection work in JVM? • Explain volatile and synchronized in multithreading • Deep copy vs Shallow copy • How does the Java memory model work (Heap, Stack, Metaspace)? 𝗦𝗽𝗿𝗶𝗻𝗴 & 𝗦𝗽𝗿𝗶𝗻𝗴 𝗕𝗼𝗼𝘁 • What is Dependency Injection? How does Spring handle it internally? • Difference between @Component, @Service, and @Repository • How does Spring Boot auto-configuration work? • Exception handling best practices in REST APIs • How to secure REST APIs (JWT, OAuth2)? 𝗝𝗣𝗔 / 𝗛𝗶𝗯𝗲𝗿𝗻𝗮𝘁𝗲 • Difference between Lazy and Eager loading • What are N+1 query problems? How to solve them? • How does Hibernate manage transactions? • Entity lifecycle states (Transient, Persistent, Detached, Removed) 𝗦𝗤𝗟 & 𝗗𝗮𝘁𝗮𝗯𝗮𝘀𝗲 • Write a query to find the 2nd highest salary from Employee table • Difference between INNER JOIN, LEFT JOIN, RIGHT JOIN • What are indexes? Clustered vs Non-clustered • How to optimize slow queries? 𝗗𝗦𝗔 / 𝗣𝗿𝗼𝗯𝗹𝗲𝗺 𝗦𝗼𝗹𝘃𝗶𝗻𝗴 • Implement LRU Cache • Detect a cycle in a linked list • Find longest substring without repeating characters • Merge overlapping intervals • Design a rate limiter 𝗦𝘆𝘀𝘁𝗲𝗺 𝗗𝗲𝘀𝗶𝗴𝗻 • Design a URL Shortener like bit.ly • How would you scale a notification service? • Difference between Monolith vs Microservices • Use of API Gateway and Load Balancer • CAP Theorem explanation with real-world examples Tip: These are not just “questions to memorize”. You should be able to explain concepts, trade-offs, and real project scenarios around them. That’s what matters in 20–25 LPA interviews. #sde1 #sde2 #sde3 #sde4 #hiring #layoff #jobHunt Read “Frequently Asked Interview Questions – SDE (Java/Spring Boot) Compensation Bracket: ₹20–25 LPA…“ by Coding Ninja on Medium: https://lnkd.in/gxVCP3tw

🚀 Preparing for Backend / SDE interviews (Java + Spring Boot) in the ₹20–25 LPA bracket? Here’s a curated list of frequently asked topics that interviewers dig deep into 👇 ⚡ 𝐂𝐨𝐫𝐞 𝐉𝐚𝐯𝐚 1. HashMap vs Hashtable vs ConcurrentHashMap 2. How Garbage Collection works in JVM 3. volatile vs synchronized in multithreading 4. Deep copy vs Shallow copy 5. Java Memory Model (Heap, Stack, Metaspace) 🌱 𝐒𝐩𝐫𝐢𝐧𝐠 & 𝐒𝐩𝐫𝐢𝐧𝐠 𝐁𝐨𝐨𝐭 6. Dependency Injection & how Spring handles it internally 7. Difference: @Component, @Service, @Repository 8. Spring Boot auto-configuration explained 9. REST API exception handling best practices 10. Securing REST APIs (JWT, OAuth2) 🗄️ 𝐉𝐏𝐀 / 𝐇𝐢𝐛𝐞𝐫𝐧𝐚𝐭𝐞 11. Lazy vs Eager loading 12. N+1 query problem & solutions 13. Transaction management in Hibernate 14. Entity lifecycle states (Transient, Persistent, Detached, Removed) 🛢️ 𝐒𝐐𝐋 & 𝐃𝐚𝐭𝐚𝐛𝐚𝐬𝐞 15. Query to find 2nd highest salary 16. INNER JOIN vs LEFT JOIN vs RIGHT JOIN 17. Indexes: Clustered vs Non-clustered 18. How to optimize slow queries 💡 𝐃𝐒𝐀 / 𝐏𝐫𝐨𝐛𝐥𝐞𝐦 𝐒𝐨𝐥𝐯𝐢𝐧𝐠 19. Implement LRU Cache 20. Detect cycle in linked list 21. Longest substring without repeating characters 22. Merge overlapping intervals 23. Design a rate limiter 🏗️ 𝐒𝐲𝐬𝐭𝐞𝐦 𝐃𝐞𝐬𝐢𝐠𝐧 24. Design a URL shortener (bit.ly) 25. Scaling a notification service 26. Monolith vs Microservices trade-offs 27. Role of API Gateway & Load Balancer 28. CAP Theorem with real-world examples 💡 Tip: 𝘛𝘩𝘦𝘴𝘦 𝘢𝘳𝘦𝘯’𝘵 “𝘮𝘶𝘨-𝘶𝘱” 𝘲𝘶𝘦𝘴𝘵𝘪𝘰𝘯𝘴. 𝘍𝘰𝘳 𝘩𝘪𝘨𝘩𝘦𝘳-𝘤𝘰𝘮𝘱 𝘳𝘰𝘭𝘦𝘴 (20–25 𝘓𝘗𝘈), 𝘤𝘰𝘮𝘱𝘢𝘯𝘪𝘦𝘴 𝘭𝘰𝘰𝘬 𝘧𝘰𝘳 𝘤𝘰𝘯𝘤𝘦𝘱𝘵 𝘤𝘭𝘢𝘳𝘪𝘵𝘺, 𝘵𝘳𝘢𝘥𝘦-𝘰𝘧𝘧 𝘥𝘪𝘴𝘤𝘶𝘴𝘴𝘪𝘰𝘯𝘴, 𝘢𝘯𝘥 𝘳𝘦𝘢𝘭 𝘱𝘳𝘰𝘫𝘦𝘤𝘵 𝘢𝘱𝘱𝘭𝘪𝘤𝘢𝘵𝘪𝘰𝘯𝘴. Wishing all job seekers & interview preppers the best! 🚀 #sde1 #sde2 #sde3 #hiring #jobhunt #backend #java #springboot #interview #softwareEngineer #softwareDeveloper

🚀 Day 4 of my #100DaysOfDSAinJava Journey  🔹 Today I learned the **Two-Pointer Technique** to reverse an array.   👉 Concept: Use two pointers (start and end), swap elements, and move inward.   👉 Time Complexity: O(n)   👉 Space Complexity: O(1)   👉 Problem Solved: Reversed an array in place.  💻 Implemented in Java.   Also did a step-by-step dry run to visualize the swaps! Solution 💡 public class Day4_ReverseArray {   public static void reverseArray(int[] arr) {     int left = 0, right = arr.length - 1;     while (left < right) {       // swap elements       int temp = arr[left];       arr[left] = arr[right];       arr[right] = temp;       left++;       right--;     }   }   public static void main(String[] args) {     int[] arr = {10, 20, 30, 40, 50};     System.out.print("Original Array: ");     for (int num : arr) {       System.out.print(num + " ");     }     reverseArray(arr);     System.out.print("\nReversed Array: ");     for (int num : arr) {       System.out.print(num + " ");     }   } } 🖥️ Output: Original Array: 10 20 30 40 50  Reversed Array: 50 40 30 20 10 #DataStructures #ProblemSolving #CompetitiveCoding #SoftwareDeveloper #Fresher #OOPS #WebDevelopment #fullStack #FrontendDeveloper #BackendDeveloper #JavaDeveloper #DSA #Java #100DaysChallenge #Algorithms #HR #Hiring #IT #ProblemSolving #Bengaluru #Spring #Hibernate #HTML5 #CSS3 #JavaScript #React #MySql #SQL #AI #ArtificialIntelligence #DataStructuresAndAlgorithms

💡 Java is Always Pass-by-Value Even after 4 years of writing Java, revisiting the basics during my SDE-2/SDE-3 prep reminded me of this key fact: ✅ Java passes a copy of the reference, not the reference itself. Changing object state ➝ ✅ reflects outside Reassigning reference ➝ ❌ doesn’t affect caller This simple distinction has made my debugging cleaner and interview solutions more precise. 💬 Which “basic” concept recently made you rethink your code? #Java #JavaDeveloper #SDE2 #SDE3 #CodingInterview #InterviewPreparation #SoftwareEngineering #DSA #ProblemSolving #CareerGrowth #Hiring #TechJobs

🛠 PayPal Interview Experience – SDE-1 (Java Backend) 📌 Application Mode: Through Referral 💻 Interview Mode: Virtual (Online) 🎯 Role: Software Development Engineer – 1 (Backend) 🧩 DSA / Problem Solving 1️⃣ Grid pathfinding with '+' and '0' → check reachability & shortest path. 2️⃣ Streaming k-th largest element after each insertion. 3️⃣ Intersection point of two singly linked lists (O(1) space). 4️⃣ k-th element from the end in a generic linked list. 5️⃣ Modified Kadane’s Algorithm → return start & end indices. 6️⃣ Reverse a linked list in groups of size k. 7️⃣ Remove duplicates from an unsorted linked list. 8️⃣ Count numbers ≤ N with odd number of divisors. 9️⃣ Large-scale anagram check (billions of characters). 🔟 Sliding window: top 10 most frequent APIs in last 10 minutes. 1️⃣1️⃣ Minimum window substring containing all characters of a pattern. 1️⃣2️⃣ Implement LFU Cache with O(1) operations. 💻 Core Java & Concurrency 1️⃣3️⃣ TreeSet with mixed types (int, String, Object) → compile vs runtime. 1️⃣4️⃣ synchronized vs ReentrantLock vs StampedLock vs ReadWriteLock. 1️⃣5️⃣ Implement thread-safe LRU cache without ConcurrentHashMap. 1️⃣6️⃣ Why does list.stream().map(List::stream) return List<Stream<T>>? 1️⃣7️⃣ Why Java doesn’t support pointers → impact on memory safety. 1️⃣8️⃣ Explain Java Memory Model & happens-before relation in concurrency. 1️⃣9️⃣ Difference between HashMap, ConcurrentHashMap, and Hashtable. 2️⃣0️⃣ Implement a producer–consumer system using BlockingQueue. 2️⃣1️⃣ Explain volatile vs Atomic variables in multithreading. 🏗 System / Low-Level Design 2️⃣2️⃣ Design a digital wallet (transactions, consistency, scaling). 2️⃣3️⃣ Design a rate limiter (per-user, per-API key). 2️⃣4️⃣ Design a logging system (collection, indexing, querying). 2️⃣5️⃣ Design a nearest ATM finder (location-based queries). 2️⃣6️⃣ Handle a sudden 10x traffic spike in backend services. 2️⃣7️⃣ Design a retry mechanism with exponential backoff. 2️⃣8️⃣ Design a notification service (email/SMS) ensuring reliability & scalability. #Java #BackendDevelopment #SoftwareEngineering #SDE #SpringBoot #Microservices #SystemDesign #CodingInterview #TechInterviews #DSA #Programming #SoftwareDeveloper #ITJobs #CareerGrowth #TechCommunity #Hiring #JobSearch #HRCommunity #Recruitment #TalentAcquisition #Leadership #ProductManagement #EngineeringLeadership #TechLead #Scalability #PerformanceEngineering #JavaDeveloper #BackendEngineer #SoftwareDesign #CloudComputing #APIDesign #ProblemSolving #CleanCode #ObjectOrientedProgramming #Concurrency #Multithreading #DatabaseDesign #TechCareers #TechLife #Innovation

🛠 PayPal Interview Experience – SDE-1 (Java Backend) 📌 Application Mode: Through Referral 💻 Interview Mode: Virtual (Online) 🎯 Role: Software Development Engineer – 1 (Backend) 🧩 DSA / Problem Solving 1️⃣ Grid pathfinding with '+' and '0' → check reachability & shortest path. 2️⃣ Streaming k-th largest element after each insertion. 3️⃣ Intersection point of two singly linked lists (O(1) space). 4️⃣ k-th element from the end in a generic linked list. 5️⃣ Modified Kadane’s Algorithm → return start & end indices. 6️⃣ Reverse a linked list in groups of size k. 7️⃣ Remove duplicates from an unsorted linked list. 8️⃣ Count numbers ≤ N with odd number of divisors. 9️⃣ Large-scale anagram check (billions of characters). 🔟 Sliding window: top 10 most frequent APIs in last 10 minutes. 1️⃣1️⃣ Minimum window substring containing all characters of a pattern. 1️⃣2️⃣ Implement LFU Cache with O(1) operations. 💻 Core Java & Concurrency 1️⃣3️⃣ TreeSet with mixed types (int, String, Object) → compile vs runtime. 1️⃣4️⃣ synchronized vs ReentrantLock vs StampedLock vs ReadWriteLock. 1️⃣5️⃣ Implement thread-safe LRU cache without ConcurrentHashMap. 1️⃣6️⃣ Why does list.stream().map(List::stream) return List<Stream<T>>? 1️⃣7️⃣ Why Java doesn’t support pointers → impact on memory safety. 1️⃣8️⃣ Explain Java Memory Model & happens-before relation in concurrency. 1️⃣9️⃣ Difference between HashMap, ConcurrentHashMap, and Hashtable. 2️⃣0️⃣ Implement a producer–consumer system using BlockingQueue. 2️⃣1️⃣ Explain volatile vs Atomic variables in multithreading. 🏗 System / Low-Level Design 2️⃣2️⃣ Design a digital wallet (transactions, consistency, scaling). 2️⃣3️⃣ Design a rate limiter (per-user, per-API key). 2️⃣4️⃣ Design a logging system (collection, indexing, querying). 2️⃣5️⃣ Design a nearest ATM finder (location-based queries). 2️⃣6️⃣ Handle a sudden 10x traffic spike in backend services. 2️⃣7️⃣ Design a retry mechanism with exponential backoff. 2️⃣8️⃣ Design a notification service (email/SMS) ensuring reliability & scalability. #Java #BackendDevelopment #SoftwareEngineering #SDE #SpringBoot #Microservices #SystemDesign #CodingInterview #TechInterviews #DSA #Programming #SoftwareDeveloper #ITJobs #CareerGrowth #TechCommunity #Hiring #JobSearch #HRCommunity #Recruitment #TalentAcquisition #Leadership #ProductManagement #EngineeringLeadership #TechLead #Scalability #PerformanceEngineering #JavaDeveloper #BackendEngineer #SoftwareDesign #CloudComputing #APIDesign #ProblemSolving #CleanCode #ObjectOrientedProgramming #Concurrency #Multithreading #DatabaseDesign #TechCareers #TechLife #Innovation

💡 J.P. Morgan Interview Questions – SDE-1 (Java Backend) 📌 Application Mode: Careers Portal 💻 Interview Mode: Virtual (Online) 🎯 Role: Software Development Engineer – 1 (Backend, Java) 🧩 DSA 1️⃣ Find all subarrays with sum = K in an integer array. 2️⃣ Implement an LRU cache without using LinkedHashMap. 3️⃣ Detect a cycle in an undirected graph. 4️⃣ Implement kth smallest element in a BST. 5️⃣ Given a string, return minimum window substring containing all characters of another string. 💻 Core Java & Concurrency 6️⃣ Difference between HashSet, LinkedHashSet, TreeSet. 7️⃣ Explain CopyOnWriteArrayList → when to use, when not to use. 8️⃣ Explain ThreadLocal – how it works internally, pitfalls. 9️⃣ How does ForkJoinPool differ from a regular ThreadPoolExecutor? 🔟 Explain Deadlock, Livelock, Starvation → how to prevent them in Java. 1️⃣1️⃣ Explain how CompletableFuture improves async programming. 1️⃣2️⃣ What is the difference between WeakReference, SoftReference, PhantomReference? 🌱 Spring Boot & Microservices 1️⃣3️⃣ How does Spring Boot autoconfiguration pick the right DataSource bean? 1️⃣4️⃣ Explain Spring Boot starter parent and dependency management. 1️⃣5️⃣ How do you debug lazy initialization exceptions in JPA/Hibernate? 1️⃣6️⃣ Explain how @Transactional isolation levels work in banking systems. 1️⃣7️⃣ How do you handle distributed transactions (saga pattern, 2PC)? 1️⃣8️⃣ How to implement role-based access control (RBAC) in Spring Security? 1️⃣9️⃣ How do you configure rate limiting at API Gateway level in Spring Cloud? 2️⃣0️⃣ How does Spring Cloud Circuit Breaker integrate with Resilience4j? 2️⃣1️⃣ How to detect and fix N+1 query problem in Spring Data JPA? 2️⃣2️⃣ How do you configure connection pool (HikariCP) for high-throughput services? 2️⃣3️⃣ How do you handle graceful shutdown in Spring Boot microservices (k8s readiness/liveness probes)? 🏗 Low-Level Design 2️⃣4️⃣ Design a real-time stock price aggregator (millions of updates/sec). 2️⃣5️⃣ Design a distributed cache service (like Redis). 2️⃣6️⃣ Design a chat messaging system (1:1 + group + offline delivery). 2️⃣7️⃣ Design a URL shortener (bit.ly scale). 2️⃣8️⃣ Design a notification system (multi-channel: email, SMS, push). 2️⃣9️⃣ Design a document collaboration tool (Google Docs style concurrency).  #Java #JavaBackend #BackendDevelopment #SoftwareEngineering #SDE #SpringBoot #Microservices #SystemDesign #CodingInterview #TechInterviews #DSA #Programming #SoftwareDeveloper #SoftwareArchitecture #EngineeringLeadership #TechLead #ProductManagement #ProjectManagement #HRCommunity #TalentAcquisition #Recruitment #CareerGrowth #ITJobs #TechCommunity #SoftwareEngineeringLife #CleanCode #DesignPatterns #Concurrency #Multithreading #DatabaseDesign #CloudComputing #APIDesign #PerformanceEngineering #Scalability #Innovation #TechCareers #TechLeadership #SoftwareDevelopment #Agile #DevOps #CodingLife

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