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/core-java-interview-questions/blob/main/CoreJavaQa1.md
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

Видео Core Java Interview Questions канала Chakri Codes Java