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Applet Capabilities

The previous page might have made you feel like applets are merely crippled applications. Not true! Besides the obvious feature that applets can be loaded over the network, applets have more capabilities than you might think. They have access to the API in every java.* package (subject to security restrictions) plus they have some capabilities that not even applications have.

Capabilities that Applications Don't Have

Applets get extra capabilities because they are supported by code in the application they run in. Applets have access to this support through the java.applet package, which contains the Applet class and the AppletContext, AppletStub, and AudioClip interfaces.

Here are some capabilities that applets have and applications don't:

Applets can play sounds.
See Playing Sounds(in the Writing Applets trail) for information.

Applets running within a Web browser can easily cause HTML documents to be displayed.
This is supported with the AppletContext showDocument() methods. See Communicating with the Browser(in the Writing Applets trail) for more information.

Applets can invoke public methods of other applets on the same page.
See Sending Messages to Other Applets On the Same Page(in the Writing Applets trail) for information.

More Applet Capabilities

Besides the above capabilities, applets have some more that you might not expect:
Applets that are loaded from the local file system (from a directory in the user's CLASSPATH) have none of the restrictions that applets loaded over the network do.
This is because applets that are in the user's CLASSPATH become part of the application when they're loaded.

Although most applets stop running once you leave their page, they don't have to.
Most applets, to be polite, implement the stop() method (if necessary) to stop any processing when the user leaves the applet's page. Sometimes, however, it's appropriate for an applet to continue executing. For example, if a user tells an applet to perform a complex calculation, the user might want the calculation to continue. (The user should generally be able to specify whether it should continue, though.) As another example, if an applet might be useful over multiple pages, it should use a window for its interface (and not hide the window in its stop() method). The user can then dismiss the window when it's no longer needed.

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