Learn JAVA with Real Code Examples

Java compiles to JVM bytecode, allowing it to run on any platform with a Java Virtual Machine.

It is designed around OOP principles, concurrency, security, and predictable performance.

Used in enterprise backend systems, Android apps, cloud microservices, and financial platforms.

JVM runtime and bytecode execution

Object-oriented design

Generics and type safety

Concurrency with threads/executors

Functional APIs with Streams

Data types and variables

Classes, objects, and interfaces

Inheritance and polymorphism

Generics and collections

Lambdas and streams

Exception handling

src/main/java for code

src/test/java for tests

pom.xml or build.gradle

resources/ for configs and assets

target/build/ for compiled output

Write code in .java files

Compile with javac

Run using java command

Use Maven/Gradle for builds

Deploy via JAR/WAR or containers

Beginner: Console apps

Intermediate: Spring Boot APIs

Advanced: Distributed microservices

Expert: Low-latency trading systems

More stable than JavaScript

More enterprise-ready than Python

More mature than Kotlin but more verbose

Less low-level than Go/Rust

Java 5 – Generics, annotations

Java 8 – Streams, lambdas

Java 11 – LTS release

Java 17 – Modern LTS

Java 21 – Virtual Threads (Project Loom)

JVM: Java Virtual Machine

JDK: Java Development Kit

JAR: Packaged Java archive

GC: Automated memory management