Chapter 20 Applets An applet is small a Java program that runs inside another application, usually a Web browser or an applet viewer. The JDK includes an applet viewer to help you test your applets. However, most of the time your applets will run inside a Web browser. This chapter starts with a brief history of applets and by introducing the java.applet.Applet class. However, don't use Applet directly. Instead, use a Java Swing class named javax.swing.JApplet. JApplet is a subclass of Applet and is more powerful than its parent. A Brief History of Applets