Getting Started with Java: JDK, JShell and Your First Program

Java is one of the most widely used programming languages in the world. It runs banking systems, Android apps, big-data platforms and — closer to home for integration developers — the engines behind tools like Boomi, MuleSoft and countless enterprise APIs. Learning Java gives you a language that will keep paying off for decades.

This first lesson gets you from nothing to a running program. No previous programming experience is needed.

The three words you’ll keep hearing

• JVM (Java Virtual Machine) — the engine that runs Java programs. Your code is compiled into bytecode, and the JVM runs that bytecode on Windows, macOS or Linux. That’s Java’s famous promise: write once, run anywhere.
• JDK (Java Development Kit) — everything you need to write Java: the compiler (javac), the launcher (java), JShell and the standard library. This is what you install.
• JRE — the runtime only. Modern JDKs include it, so you rarely think about it separately.

Step 1: install a JDK

Install a long-term-support (LTS) version — Java 21 is a great choice. Free builds are available from Eclipse Temurin (adoptium.net), Oracle, Amazon Corretto and others; they all behave the same for learning.

Check it worked by opening a terminal (Command Prompt or PowerShell on Windows) and typing:

java -version

You should see something like openjdk version "21...". If you get “command not found”, the JDK’s bin folder isn’t on your PATH yet — the installer usually offers to set it up.

Step 2: experiment with JShell

JShell is Java’s interactive playground: type a line, see the result instantly. It’s the fastest way to learn.

jshell

Then try:

int quantity = 24;
double price = 8.50;
quantity * price
"po-4471".toUpperCase()

JShell prints each result ($3 ==> 204.0, $4 ==> "PO-4471"). Type /exit to leave.

Tip: Keep JShell open while you work through these tutorials. Whenever you wonder “what does this do?”, try it there.

Step 3: your first program

Create a file called HelloWorld.java with this content:

// HelloWorld.java — your first Java program.
// Run it with:  java HelloWorld.java   (Java 11+ runs a single file directly)
public class HelloWorld {

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

        String name = args.length > 0 ? args[0] : "Java learner";
        System.out.println("Welcome, " + name + "!");
    }
}

What each line means

• public class HelloWorld — every Java program lives inside a class. The file name must match the public class name: HelloWorld.java.
• public static void main(String[] args) — the main method, where the program starts. args holds anything typed after the program name on the command line.
• System.out.println(...) — prints a line of text.
• String name = ... ? ... : ...; — creates a text variable. The ? : part chooses a value: if arguments were given, use the first one, otherwise use “Java learner”.
• ; — every statement ends with a semicolon. Forgetting one is the most common beginner error, and the compiler will point to it.

Step 4: run it

Since Java 11 you can run a single file directly:

java HelloWorld.java
java HelloWorld.java Chirag

Hello, World!
Welcome, Java learner!
Hello, World!
Welcome, Chirag!

For bigger projects you compile first and then run the compiled class — this is what build tools like Maven and Gradle do for you:

javac HelloWorld.java     # creates HelloWorld.class (bytecode)
java HelloWorld           # runs it on the JVM

Choosing an editor

Any text editor works, but an IDE makes Java much friendlier: IntelliJ IDEA Community (free), VS Code with the Java extension pack, or Eclipse. They highlight mistakes as you type, auto-complete methods and run programs with one click.

Common first-day errors

• error: class HelloWorld is public, should be declared in a file named HelloWorld.java — rename the file to match the class.
• error: ';' expected — a missing semicolon on the line shown (or just before it).
• cannot find symbol — a typo, or wrong capitalisation. Java is case-sensitive: system.out is not System.out.

Try it yourself

Change the program so it prints a short receipt: your name, a product, a quantity and the total price (quantity × price).

public class Receipt {
    public static void main(String[] args) {
        String customer = "Acme Ltd";
        String product = "AX-200";
        int quantity = 24;
        double price = 8.50;
        System.out.println("Customer: " + customer);
        System.out.println(quantity + " x " + product + " = " + (quantity * price));
    }
}

Key takeaways

• Install a JDK (Java 21 LTS is a good default) and check it with java -version.
• JShell lets you try any line of Java instantly.
• Every program needs a class and a main method; the file name matches the public class.
• java File.java runs a single file; javac + java is the compile-then-run route.