Introduction to Java

What is Java?

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

// 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 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!");
    }
}

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!

Quick Quiz: Test Your Knowledge