Java Interview Questions 2026
Java interview questions for backend development roles at enterprises. Covers OOP, collections, concurrency, Spring Boot, and microservices.
Explain the Java Memory Model and garbage collection.
Java memory is divided into Heap (objects) and Stack (method frames, primitives). Heap has: Young Generation (Eden + Survivor spaces) for new objects, Old Generation (Tenured) for long-lived objects. GC algorithms: G1GC (default Java 9+, good for large heaps), ZGC (low latency, Java 15+), Parallel GC (throughput focused). For tuning: monitor GC pause times with -verbose:gc, increase heap with -Xms/-Xmx, and use GCEasy.io for analysis.
What is the difference between ArrayList and LinkedList?
ArrayList uses a dynamic array: O(1) random access by index, O(n) insertion/deletion in the middle. LinkedList uses doubly-linked nodes: O(1) insertion/deletion at known positions, O(n) random access. Use ArrayList for most cases (better cache locality, less memory). Use LinkedList only when you frequently insert/delete at both ends (implement Queue/Deque). In interviews, always ask about the access pattern before choosing.
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