A very simple applet draws a rectangle and prints a string something on the screen.

public class MyApplet extends JApplet{ 

    private String str = "StackOverflow";

    @Override
    public void init() {
        setBackground(Color.gray);
    }
    @Override
    public void destroy() {}
    @Override
    public void start() {}
    @Override
    public void stop() {}
    @Override
    public void paint(Graphics g) {
        g.setColor(Color.yellow);
        g.fillRect(1,1,300,150);
        g.setColor(Color.red);
        g.setFont(new Font("TimesRoman", Font.PLAIN, 48));
        g.drawString(str, 10, 80);
    }
}

The main class of an applet extends from javax.swing.JApplet.

Before Java 1.2 and the introduction of the swing API applets had extended from java.applet.Applet.

Applets don’t require a main method. The entry point is controlled by the life cycle. To use them, they need to be embedded in a HTML document. This is also the point where their size is defined.

<html>
  <head></head>
  <body>
     <applet code="MyApplet.class" width="400" height="200"></applet>
  </body>
</html>