Since an Applet is a subclass of AWT Panel class, applets can contain other Components, just as a Panel can contain. As Panels, Applets also do participate in AWT drawing and the event hierarchy.

This is having two implications. First, unlike GUI-based applications, applets dont have to create the window to display themselves on. (They can do, if they have a good reason, but usually they just display themselves within the browser window ). Second, depending on browsers implementation, the applet's components may not be shown unless an applet calls the validate() after adding components to itself. Fortunately, calling validate() cannot hurt.

Since the <APPLET> tag requires the applet's width and height to be specified, and because browsers not necessarily allow applets to resize themselves, applets should make with fixed amount of space that may not be ideal. Even if amount of space is ideal for one platform, the platform-specific parts of applet (such as buttons) may require a different amount of space on the other platform. You can do compensate by recommending the pages that includes your applet specify a little more space than be necessary, and by using the flexible layouts, like GridBagLayout and BorderLayout, which adapt well to extra space.

An Applet class do provide a convenient form of getImage() which lets you to specify a base URL as one argument, followed by second argument which specifies an image file location, relative to base URL. The Applet getCodeBase() and getDocumentBase() methods do provide the base URLs which the most applets use. Images that the applet always needs, or needs to rely on a backup, are usually specified relative to where an applet's code was loaded from. Images which are specified by an applet user (often with the parameters in HTML file) are usually relative to page which includes the applet (document base).

Applets can perform several things to decrease the perceived startup time. Their Applet subclass can be small one which immediately displays the status message. And, if some of the applet classes or data are not used right away, the applet can preload classes or the data by referencing them before they are needed. Cosider for example, the AppletButton class, at the beginning of the main thread, gets the class object for the window the button brings up. Here its main purpose is to make sure that the class is valid, but an added benefit is getting the class object force the class file to be loaded before it is needed, which makes the class instantiating much quicker than if a class still had to be loaded.