What is Java and How Does it Work?

What is Java?

Java is a class-based, object-oriented language designed to be "write once, run anywhere." Code compiles to bytecode that runs on the Java Virtual Machine (JVM), so the same program runs on Windows, Mac, Linux, and Android.

How Java Runs

1. You write .java source files.
2. javac compiles them to .class bytecode.
3. The JVM interprets/JIT-compiles bytecode to machine code at runtime.

Hello World

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello, Java!");
    }
}

Where Java is Used

• Enterprise backends — Spring Boot powers banks & large companies.
• Android apps — the original Android language.
• Big data — Hadoop, Spark, Kafka are JVM-based.

FAQs

Java vs JavaScript?

Completely different languages — similar name only. More in our Java guides.

Is Java still relevant?

Very — it powers a huge share of enterprise and Android software with strong job demand.