What Can Go Wrong

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What Can Go Wrong

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Because of the many factors involved, it may take a few tries to get things right. Here are some common JavaSketchpad mishaps and steps you can take to avoid them.

More detailed information is available on the JavaSketchpad web site: http://www.dynamicgeometry.com/JavaSketchpad.html.

Unsupported Objects

Problem: When you save, Sketchpad warns you that not all objects were successfully saved to JavaSketchpad format.

Cause: Because JavaSketchpad is smaller than “desktop” Sketchpad, it supports fewer ways of defining objects than you can use in the desktop application. If your sketch contains objects that JavaSketchpad doesn’t support, Sketchpad warns you about them — and selects the unsupported objects and their children in your sketch so that you can tell which ones were not supported. (Even when your sketch has unsupported objects, Sketchpad will save the objects that JavaSketchpad does support, so you can continue testing your web page.)

To work around unsupported objects, explore different ways of constructing the same illustration. For example, at present, JavaSketchpad does not support iterations or iterated images. If your sketch contains a construction that you’ve iterated using the Transform | Iterate command, you may be able to replace it with one that you’ve iterated “manually” by actually constructing the first several iterations.

A complete list of objects supported by JavaSketchpad is available on the JavaSketchpad web site. Also, new versions of the applet—that support more and more Sketchpad objects — occasionally appear on the web site.

If your sketch or activity requires objects not supported by JavaSketchpad, you won’t be able to share that sketch as an illustration. However, you can still post your original Sketchpad sketch — your .gsp file — as a downloadable file, so that visitors who use The Geometer’s Sketchpad can download it and open it in Sketchpad, rather than in their browser.

No Preview Offered

Problem: Rather than ask whether you want to preview your file in a browser, when you save, Sketchpad warns that you saved to a folder that does not contain a copy of jsp5.jar.

Cause: Sketchpad could not locate the jsp5.jar applet to copy it to the folder with your HTML page. The original copy of the applet may have been accidentally removed from its normal location in the Sketchpad folder. Reinstall Sketchpad to restore the applet.

Non-Java Browsers

Problem: When you preview your web page in a browser, the page contains a message reading “Sorry, this page requires a Java-capable browser.”

Cause: If you have an old web browser, it may not support the Java language and, therefore, won’t work with JavaSketchpad. Contact your browser manufacturer for a newer version. Alternately, it may be that your browser supports Java, but that it’s currently set to disable Java applets. Go to your browser’s Preferences or Options to turn on support for Java applets.

Java Exception or Error Occurs

Problem: When you preview your web page in a browser, a dialog box appears saying that a Java error or “exception” occurred.

Cause: If the message goes on to say that a “class” was not found — for example “GSP.class: class not found” — then jsp5.jar is either in the wrong location or has become corrupted. (For example, vital files within it may have been accidentally deleted or moved.) Try removing jsp5.jar from the folder and then resaving your document as HTML, so that Sketchpad can copy a fresh copy of jsp5.jar to the destination folder.

If the error message says something else, a different problem has occurred. While JavaSketchpad has been extensively tested on current versions of Internet Explorer, FireFox, and Safari, older browsers are erratic in their support of Java, and other browsers may have similar problems. (Java is a relatively new language and undergoes frequent modifications; different browsers support it to different degrees.) Check with your browser manufacturer to see if a more recent version of your browser is available. Errors or exceptions may also indicate a problem with JavaSketchpad itself. Visit the JavaSketchpad web site to see if a more recent version of the applet is available.

Appearance Discrepancies

Problem: Your sketch saves correctly and previews in your browser, but certain details in the JavaSketchpad illustration — such as choice of fonts, size of exact position of text — do not match your original sketch.

Cause: These minor discrepancies are inevitable in Java applets, where less sophisticated graphic and text services are available to an applet than to a nonapplet program (like your browser or desktop Sketchpad). What you sacrifice in appearance flexibility you gain in generality: Applets like JavaSketchpad work well on a much wider variety of computers than are capable of running the full desktop version of Sketchpad.