This page discusses the few issues that are particular to applet GUIs. Some of the information in this section might not make sense until you've read the Creating a User Interface trail. That trail discusses all the GUI concepts referred to on this page and gives many examples of applet GUIs. An Applet is a Panel . Because Applet is a subclass of the AWT Panel class , applets can contain other Components , just as any Panel can.
Applets appear in pre-existing browser windows.
This has two implications. First, unlike GUI-based applications, applets don't have to create a window to display themselves in. They can, if they have a good reason, but they often just display themselves within the browser window. Second, depending on the browser implementation, your applet's components might not be shown unless your applet calls validate after adding components to itself. Fortunately, calling validate can't hurt.