LED Sign Fequently Asked Questions

August 11, 1996

These are some frequently asked questions about LED Sign. I will continue to add new questions/answers as they arise to the FAQ at the new LED Sign home page. So, if you don't find the answer to your question here, check the FAQ at the link above.

Note

My time is devoted primarily to the O'Reilly WebSite Web Server. I get an enormous amount of email, and I read a dozen or so usenet newsgroups and mailing lists. Bottom line is that I cannot provide technical support for this package. I hope you can understand. Darrick has provided a reasonably complete set of documentation files, to which I have added to make them represent V3.1. Like Darrick, I will delete any email I receive asking for technical support. If you have questions about how to set up an applet, check the java site at http://www.javasoft.com/. If you have other problems, I would suggest checking the usenet newsgroups comp.lang.java.*.


security violation:security.protocol:file

Q:
I've installed LED Sign on my machine as the instructions have specified, but when I load the page I get an "Applet LED can't start: security violation:security.protocol:file" error. What is wrong?
A:
Usually this is caused by loading the file locally with "file://..." or selecting "open file" from the file menu on Netscape 2.x or early 3.x betas. According to Darrick, you cannot run LED Sign locally with these versions of Netscape.

I have tested LED Sign 3.0 with Netscape 3.0b7 and Internet Explorer 3.0B2, and it will work reading the scripts, probably (!) because the new packaged format and directory structure has the scripts and fonts in subdirectories below the classes. I no longer have old Netscapes so maybe this will work with them as well. Let me know...


Commercial use of LED Sign

Q:
I read in the COPYRIGHT that LED Sign is for non-profit use only. Can I use it on my company homepage?
A:
Yes. You may use LEDSign on a commercial homepage. What the "non-profit" part means is that you cannot sell LED Sign in any way. LED Sign is freeware, and I (darrick Browne) retain all rights to it. It is NOT public domain. This means you cannot sell it in an internet software "bundle", sell it in any type of commercial distribution, or sell it to clients. If you are a web page designer and do consulting, you may charge your clients for the time it took you to set up LED Sign, but you may not charge for LED Sign itself.

error: java.lang.ClassFormatError

Q:
When I load my page with LED Sign on it, I get a "error: java.lang.ClassFormatError". What is wrong?
A:
Contact your web server administrator. The error is caused by the web server not knowing what a ".class" file is serving to the browser incorrectly. Some web servers have problems with this, others do not.

Applet can't start: applet not initialized

Q:
I downloaded the LED Sign kit and have it installed on my machine. When I try to load the page in Netscape I get a "Applet can't start: applet not initialized" error and the applet does not run. How do I fix this?
A:
This problem can be caused by two situations:

  1. You are using Netscape 2.x or early betas of Netscape 3.0. For these versions, you need to load the page over a URL with "http://...". If you are loading it localy with "file://..." you will get the initialization and security errors.

  2. You need to make sure that all the file names and paths are correct in the <applet> tag in the html page. If the applet can't find the files that it needs it won't be able to run and it will give the "init" error.
          <applet codebase="../../../../.." 
                  code="com.dc3.applet.LEDSign.LED.class" 
                  width=519 height=64>
             <param name="script" value="../scripts/Demo.led">
             <param name="font" value="../fonts/default.font">
             <param name="border" value="3">
             <param name="bordercolor" value="100,130,130">
             <param name="spacewidth" value="3">
             <param name="wth" value="100">
             <param name="ht" value="9">
             <param name="ledsize" value="3">
          </applet>
    This is the example tag that is found in LED.html in the distribution. I used relative paths so that the docs would load the LED sign sample even when the LED.html file was loaded ad a file (works with Netscape 3.0b7 and later, Internet Explorer 3.0B2 and later). I know this is confusing if you don't understand how the CLASSPATH and CODEBASE features of Java work. Please see This is a packaged applet.

    The tags that are critical are codebase, code, script, and font. These paths and files must be correct including capitialization. Codebase is the path to where the com directory created during installation can be found. Code is the main bytecode "executable" file. Code should always be "com.dc3.applet.LEDSign.LED.class". Script is the LED script that the sign will run. And font is the font file that the sign will use to display the characters.

    If you are working on a Win95/NT system and your ZIP program changes file name size (truncates to the MS-DOS 8.3) or changes capitalization, find a 32-bit ZIP program such as WinZip 6.0a (available at most NT/95 download sites), and reinstall the package.


error: ClassNotFound Exception

Q: When I try to load the applet, I get a "ClassNotFound" error in the status bar of Netscape. What is causing this? A: The codebase path in the <applet> tag is incorrect. Just correct the path to point to the directory where all the .class files for LED Sign are located and it should run fine. -----------------------------