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What is Java?

Java is a high-level, object-oriented programming language created by James Gosling at Sun Microsystems in 1995. Its key philosophy is "Write Once, Run Anywhere" (WORA) — meaning Java code compiled on one platform can run on any device that has a Java Virtual Machine (JVM). Today, Java powers everything from Android phones to enterprise banking systems.

Why Learn Java?

Platform Independent — Java runs on Windows, macOS, Linux, and mobile devices

Huge Job Market — Java developers are among the most in-demand worldwide

Android Development — Android apps are primarily built with Java/Kotlin

Enterprise Ready — Banks, healthcare, and governments rely on Java

Large Community — Millions of developers, extensive libraries, and frameworks

Object-Oriented — Teaches clean, modular, and reusable code design

Your First Java Program

Example

// Every Java program starts with a class
public class HelloWorld {
    // The main method — where your program starts running
    public static void main(String[] args) {
        // println prints text to the screen
        System.out.println("Hello, World!");
        System.out.println("Welcome to Java Programming!");
        System.out.println("Let's start learning!");
    }
}

Try It Yourself: Hello World

Try It Yourself: Hello WorldJava

Java Editor

✓ ValidTab = 2 spaces

// Try changing the message below!
public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
        System.out.println("I am learning Java!");
        System.out.println("Java is awesome!");
    }
}

Output

Click ▶ Run to see the result

Edit the code on the left, then click Run

Java|8 lines|257 chars|✓ Valid syntax

UTF-8

How Java Works — Step by Step

Step 1: You write Java code in a .java file (source code)

Step 2: The Java Compiler (javac) converts it to .class file (bytecode)

Step 3: The JVM (Java Virtual Machine) reads the bytecode and runs it

Step 4: The JVM translates bytecode to machine code for your specific OS

This is why Java is 'platform independent' — the JVM handles different platforms!

Introduction to Java