Chapter 9. The Network Methods of java.applet.Applet
Undoubtedly you’re familiar with
applets, Java programs that can be embedded on a web page and run in
a secure environment within a browser. All applets extend the
java.applet.Applet class, which includes a number
of methods that perform network-related operations. These methods
allow an applet to find out where it came from, download images and
sounds from a web server, and track the progress of the download.
This chapter discusses the interaction between applets and the
network. It doesn’t provide an introduction to the
Applet class as a whole; for that, see an
introductory book such as Niemeyer and Peck’s
Learning Java (O’Reilly & Associates,
Inc., 2000).
Using java.applet.Applet to Download Data
The
methods of the Applet class discussed in this
section are really just thin veneers over equivalent methods in the
java.applet.AppletStub and
java.applet.AppletContext interfaces. These
interfaces describe services that the web browser or applet viewer
provides to applets. The exact classes that implement these
interfaces are undocumented and vary from implementation to
implementation. Applets that you instantiate yourself (for example,
an applet that also runs as an application by supplying a
main( ) method that calls the applet’s
init( ) and start( ) methods)
will generally have null AppletStub and
AppletContext members. Therefore, if you try to
use these methods in such an applet, a
NullPointerException will be thrown.
Figuring ...
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