java-backend-interview-questions

What problem does it solve?

This Skill compiles and structures Java backend interview topics and coding best practices to help professionals study efficiently and answer questions confidently.

Core Features & Use Cases

• Comprehensive topic coverage: Java fundamentals (serialization, exceptions, polymorphism, parameter passing, overloading vs overriding, inner classes), interfaces vs abstract classes, wrapper types, String handling, Java 8+/11+/17+/21+/25 features, JDK vs JRE, JDK tools, hashCode/equals, dynamic proxies, JDK proxies vs CGLIB, annotations, reflection, immutability, SPI, generics, deep vs shallow copy, class loading, parent delegation model, BigDecimal precision, new String object creation, final/finally/finalize, encoding issues, ProcessBuilder, thread start pitfalls, Stack vs Queue, Optional, I/O, networking, primitive types, autoboxing/unboxing, Iterator, runtime vs compile-time exceptions, inheritance, encapsulation, access modifiers, static vs instance, for vs foreach, wait vs sleep, Java vs Go, Object methods, bytecode, BIO/NIO/AIO, Channel, Selector, Float comparisons, POJO/VO/DTO/DAO/BO, data structures and collections, HashMap internals/performance, Hash collisions, ArrayList/LinkedList differences, expansion, HashSet vs HashMap, HashMap vs Hashtable, ConcurrentHashMap vs Hashtable, CopyOnWriteArrayList, List implementations, arrays vs linked lists, load factor 0.75, powers of two, network protocols (TCP/IP, OSI, HTTP versions, HTTP vs HTTPS, HTTP vs RPC, TCP vs UDP, stickiness/packet framing), Spring (IOC, AOP, circular dependencies, three-level cache reasons, beans lifecycle, MVC principles, DI), MyBatis, MySQL indexes and non-indexed scenarios, Redis data structures and strategies, Java concurrency (thread pools, locks, synchronization, NIO/Netty performance, concurrency utilities, volatile, thread life cycle, ABA), messaging queues, microservices, databases, design patterns (singleton), system design (seckill, short URLs, distributed IDs, RPC design), JVM, troubleshooting, CPU profiling, and more.
• Practical guidance: Provides coding best practices, patterns, and troubleshooting tips with references to targeted material for deep dives.
• Use-case oriented: Suitable for interview prep, onboarding, and as a fast-reference during technical interviews or code reviews.

Quick Start

Use this Skill as a study framework: skim the high-level topics, then dive into the linked references for thorough understanding and hands-on examples.