Core Java Interview Questions

Core Java Interview QA Part 1 What you’ll learn: Clear differences between JVM, JRE, and JDK with modern distribution notes Why Java isn’t 100% OO and how primitives/wrappers impact design and performance Exact breakdown of public static void main(String[] args) == vs equals() with String and Integer cache nuances Autoboxing/unboxing performance traps and NullPointerException risks Default values for instance fields vs local variables The real meaning of “Java is pass-by-value” with reference copies String vs StringBuilder vs StringBuffer, interning, and loop concatenation costs Package purpose, structure, and package-private visibility OOP pillars, method overloading vs overriding with examples Why static methods can’t be overridden (they’re hidden) Why constructors can’t be overridden (only overloaded) and super() rules this vs super for fields and methods Step-by-step rules to implement a safe immutable class code : https://github.com/chakricodesjava/co... Timestamps 00:00 Intro and scope (Experienced focus) 00:40 JDK vs JRE vs JVM — roles, modules, WORA, jlink 03:20 Is Java 100% Object-Oriented? Primitives, wrappers, autoboxing 05:00 public static void main(String[] args) — reflection, static, exit codes 06:40 == vs equals() — Strings, Integer cache, correctness pitfalls 09:20 Autoboxing/Unboxing — performance and NPE pitfalls with code 11:30 Default Values — instance vs local variables 11:50 Pass-by-Value — reference copy explained with examples 15:40 String vs StringBuilder vs StringBuffer — immutability, interning, loops 18:40 Packages — namespace, directory structure, imports 20:10 OOP Pillars — encapsulation, inheritance, polymorphism, abstraction; overloading vs overriding 23:50 Static Methods — hiding vs overriding 25:10 Constructors — no overriding, only overloading and super() 26:40 this vs super — fields, methods, and examples 28:40 Designing an Immutable Class — rules and code example