So the next time you visit a JavaSketchpad Web page, you'll have to wait for the applet to download again before the page's JavaSketchpad illustrations become available. But when you quit your browser or move to some other page that no longer contains a JavaSketchpad illustration, chances are your browser will flush the JavaSketchpad applet from its memory. If so, you only pay the penalty of downloading the applet once. If you go on from the triangle Web page to look at other Web pages on the server, such as pythag.htm (perhaps by following a link to them from triangle.htm), chances are your Web browser is smart enough to realize that you've already downloaded the JavaSketchpad applet and don't need to download the applet file again. At this point, the process is complete: You can begin interacting with the triangle (and with the JavaSketchpad applet that displays it). JavaSketchpad starts executing and displays the dynamic triangle specified by this geometric description. Once the applet has been downloaded (and is "resident" in your browser), your browser passes the geometric description of the triangle contained in the original triangle.htm file. Using the applet's URL, your browser connects to the Web server and downloads the JSP applet. Java-capable browsers, on the other hand, must download the JavaSketchpad applet so that it can run inside your Web browser. Older browsers don't understand Java, so they give an error message and the process stops. When your browser receives this two-part description, it first decides whether it is capable of displaying Java applets or not. The Web page provides your browser with a reference to the JavaSketchpad applet in the form of a (relative) URL that identifies the directory on the Web server where the applet is located. This description contains two parts: the geometric construction of the triangle itself (written in JavaSketchpad's internal construction language) and a reference to the JavaSketchpad applet, which is the software technology that your Web browser needs in order to visualize the triangle described by the geometric construction. In this example, the triangle.htm file may contain text or pictures, but the important part of its contents for our purposes is that it contains a JavaSketchpad description of a triangle. (Whether you specify the location of the host Web page by typing in a URL or by linking to it from some other page is immaterial the JavaSketchpad process begins once a connection is forged between your Web browser and a Web server's Web page.)Īn arbitrary HTML file on the server may contain text, colors, images, etc., all of which will appear on your browser as the page is loaded. In this case, the host Web page is the file triangle.htm, which is located on the server. When you visit this page, your browser establishes a connection with a remote machine (the Web server), using a URL to specify both the name of the host machine on the Internet and the name and location of the Web page, located on that machine, that you wish to view. The right side of the illustration represents your Web browser, which is viewing a Web site that contains a JavaSketchpad triangle. The following illustration diagrams the typical set of interactions required to create a JavaSketchpad (JSP) triangle in your Web browser. When you look at a Web page that includes a JavaSketch, many components are interacting behind the scenes to bring Dynamic Geometry to your desktop.
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