The HelloWorld applet shown next is a Java class that displays the string "Hello World".
Following is the source code for the HelloWorld applet:
import javax.swing.JApplet;
import javax.swing.SwingUtilities;
import javax.swing.JLabel;
public class HelloWorld extends JApplet {
    //Called when this applet is loaded into the browser.
    public void init() {
        //Execute a job on the event-dispatching thread; creating this applet's GUI.
        try {
            SwingUtilities.invokeAndWait(new Runnable() {
                public void run() {
                    JLabel lbl = new JLabel("Hello World");
                    add(lbl);
                }
            });
        } catch (Exception e) {
            System.err.println("createGUI didn't complete successfully");
        }
    }
}
An applet such as this is typically managed and run by the Java Plug-in software in the browser.
Download source code for the Hello World example to experiment further.