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Java Hello World

Before you write a single line of code, there are a couple of things you'll want to have set up. Nothing complicated — just the basics.

What You'll Need

  • Java Development Kit (JDK) — this is the core software that lets you write and run Java programs. You can grab it from Oracle's website.
  • A text editor or IDE — technically, you could write Java in Notepad, but an IDE like IntelliJ IDEA or Eclipse makes life a lot easier with things like auto-complete, error highlighting, and built-in tools for compiling and running your code.

Once those are installed, you're ready to go. Let's write your very first Java program: the classic "Hello World."

Setting Up Your File

Open your IDE or text editor and create a new file with a .java extension. For this walkthrough, we'll call it HelloWorld.java.

Writing the Code

Here's all it takes to print "Hello World" to the screen:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello World");
    }
}

That's the whole program. Now let's slow down and go through it piece by piece so it actually makes sense — not just something you copy and paste.

Breaking Down the Code

The Class Declaration

public class HelloWorld {

Every Java program lives inside at least one class — there's no way around it. Here, HelloWorld is the name of our class, which you can think of as a blueprint for creating objects. The public keyword is an access modifier, and it basically controls who's allowed to see and use this class.

The Main Method

public static void main(String[] args) {

This line matters a lot — it's the entry point of your program, meaning it's the first thing that runs when your code executes. Let's unpack each part:

  • public — again, an access modifier, making this method reachable from anywhere.
  • static — this means the method belongs to the class itself, not to any specific object. That's why you can run it without first creating a HelloWorld object.
  • void — tells Java this method doesn't hand back any value when it's done.
  • String[] args — an array of strings that lets your program accept input from the command line. You won't need it for this example, but it's there for when you do.

Printing the Message

System.out.println("Hello World");

This is the line that actually does something visible. Here's what's going on under the hood:

  • System — a built-in class that gives you access to system-level resources.
  • out — a member of System that's connected to your console output.
  • println — a method that prints whatever you pass it, then moves to a new line afterward.

Running Your Program

Writing the code is only half the story — now you need to compile and run it.

Step 1: Compile the Code

Save your file, then open a terminal (or command prompt on Windows) and navigate to the folder containing HelloWorld.java. Run this command:

javac HelloWorld.java

This takes your human-readable Java code and turns it into bytecode — a format the Java Virtual Machine (JVM) can actually run. If nothing shows up as an error, you're in good shape. You should now see a new file called HelloWorld.class sitting in the same folder.

Step 2: Run the Program

Now, execute it with:

java HelloWorld

If everything went smoothly, your terminal should display:

Hello World

And that's it — you've officially written, compiled, and run your first Java program. It might look tiny, but every Java application you'll ever build, no matter how complex, follows this same basic pattern: write the code, compile it, run it.

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