When an Applet is created by an application it lives in (such as a web browser), the application provides it two helper objects to communicate with its environment: AppletStub and AppletContext. The AppletStub is assigned to the applet after calling its constructor but before calling its "init" method.
If you are programming an applet, you don't have to care about AppletStub implementations. Just remember to avoid calling applet methods from its constructor; use "init" for initialization. The applet uses AppletStub object internally when calling methods "getAppletContext", "getCodeBase", "getDocumentBase", "getParameter", "isActive", and "resize".
If you are programming an application that allows embedding applets, you have to provide an AppletStub instance for each applet, and set it using "setStub" method, before calling the "init" method.