Java How to Program Fourth Edition - DCC

Chapter 17 Networking 985
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108 } // end method getSitesFromHTMLParameters
109
110 } // end class SiteSelector
Fig. Fig. 17.2 17.2 Loading a document from a URL into a browser (part 3 of 3).
When the user selects one of the Web sites in siteChooser, the program calls method
valueChanged (lines 41–54). Line 44 obtains the selected site name from the JList.
Line 47 passes the selected site name (the key) to Hashtable method get, which locates
and returns an Object reference to the corresponding URL object (the value). The URL cast
operator converts the reference to a URL that can be assigned to reference newDocument.
Line 50 uses Applet method getAppletContext to get a reference to an
AppletContext object that represents the applet container. Line 53 uses the Applet-
Context reference browser to invoke AppletContext method showDocument,
which receives a URL object as an argument and passes it to the AppletContext (i.e.,
the browser). The browser displays in the current browser window the World Wide Web
resource associated with that URL. In this example, all the resources are HTML documents.
For programmers familiar with HTML frames, there is a second version of Applet-
Context method showDocument that enables an applet to specify the so-called target
frame in which to display the World Wide Web resource. The second version of show-
Document takes two arguments—a URL object specifying the resource to display and a
String representing the target frame. There are some special target frames that can be
used as the second argument. The target frame _blank results in a new Web browser