comp.lang.vrml FAQ

VRMLworks

comp.lang.vrml FAQ Answers
3. Problems with Java

Where do I get the VRML classes for Java?

Installing most VRML browsers will automatically install the VRML Java classes. Here are some defaults I know about:

Windows 95/Netscape Navigator and Communicator

Cosmo Player 2.1 C:\Program Files\Netscape\Navigator\Program\Plugins\Npcosmop21.zip

C:\Program Files\Netscape\Communicator\Program\Plugins\Npcosmop21.jar

WorldView 2.0 C:\Program Files\WorldView for Netscape Navigator\classes

Community Place C:\Program Files\Community Place Browser\lib\java\vsclass.zip

CCPro C:\Program Files\Blaxxun Interactive\CCPro\Java\classes

Unix

Cosmo Player 1.02
(IRIX) /usr/CosmoPlayer/classes/vrml
It's sometimes necessary to copy that directory to ~/.netscape/plugins/classes/vrml

Windows 95/Netscape Navigator and Communicator
Cosmo Player 2.1	C:\Program Files\Netscape\Navigator\Program\Plugins\Npcosmop21.zip
C:\Program Files\Netscape\Communicator\Program\Plugins\Npcosmop21.jar
WorldView 2.0	C:\Program Files\WorldView for Netscape Navigator\classes
Community Place	C:\Program Files\Community Place Browser\lib\java\vsclass.zip
CCPro	C:\Program Files\Blaxxun Interactive\CCPro\Java\classes
Unix
Cosmo Player 1.02 (IRIX)	/usr/CosmoPlayer/classes/vrml It's sometimes necessary to copy that directory to ~/.netscape/plugins/classes/vrml

Does someone know the location for the Java classes in other VRML browsers? Other platforms?

I can't get Java to run in Script nodes.
First, make sure your VRML browser supports Java in Script nodes. Cosmo Player, Community Place, and WorldView are among the browsers known to have full Java script support.

There are two classes of VRML browsers on Windows 95 and NT machines: one modifies the autoexec.bat file to add the VRML classes to your CLASSPATH environment variable. The other takes advantage of a shortcut in Netscape Navigator and Communicator that lets the plugin look for a .zip or .jar file in the Netscape plugins folder. The former kind of browser is more susceptible to CLASSPATH problems. WorldView and Community Place modify autoexec.bat and Cosmo Player uses the plugins folder.

If you've got WorldView or Community Place you'll need to follow a clever procedure devised by Jeff Harrington:
First, try typing in a DOS window this:
```
set CLASSPATH=c:\java\vrml
```
Or wherever your Java classes are. Now, from the same DOS window, test it by running Netscape from the DOS prompt:
```
CD \ 
CD "Program Files\Netscape\Navigator\Program"
```
and type:
```
Netscape
```
IF that works, then you're in business. Add as statement to your autoexec.bat like the following:
```
set CLASSPATH=c:\java\vrml;%CLASSPATH%
```
IF that doesn't work try another path name. Your problem is certain though: CLASSPATH is not assigned correctly to tell Netscape where to look for external Java classes.
Not only can you get in trouble from having too few Java classes in your CLASSPATH, you can have problems when you have too many. The safest thing to do is start from zero (nothing in CLASSPATH), read the error messages, and add classes until it works.

Let me add to this some advice from Justin Couch: there are some persistent Java problems (e.g., Java Script nodes work fine, but the EAI won't work) that can only be resolved by uninstalling Netscape and all its plugins, reinstalling it in a folder with a different name, and reinstalling your VRML plugin.

Still other problems arise when you have multiple VRML browsers that support Java scripting. There's a page at the VRMLworks that discusses multiple plugin problems.
My Java compiler says that "vrml.*" and the other VRML classes are unknown.
Your Java compiler doesn't know where your VRML classes are. If you're using javac, the command-line compiler in Sun's Java Development Kit (JDK), you'll need to set your CLASSPATH environment variable. Other Java compilers or programming environments may have a different way to set a search path, but the following will apply with some modifications for your system. The situation is further complicated by Sun's JDK 1.0x not always recognizing classes that are in zip files. And yet further complications arise because some compilers use DEVCLASSPATH instead of CLASSPATH.

Here's a solution that worked for me for javac on Windows 95:
1. Unzip your VRML classes into a new folder. See the answer to another FAQ for where to find them. For our example we'll say the folder is C:\Java\Classes. Newer versions of WinZip recognize jar files, but if you have an older version you can simply add jar files to your file types to be opened with WinZip.
2. Open a DOS shell window and change directory to the folder containing the Java code you're trying to compile.
3. Type the following to add the VRML classes and your current working directory to your CLASSPATH:
```
SET CLASSPATH=C:\Java\Classes\;.;%CLASSPATH%
```
  You may need to try DEVCLASSPATH as well.
4. Compile your file:
```
JAVAC foo.java
```
On Unix systems do the same thing, except you'll use your shell's normal way to set environment variables:
```
	# set CLASSPATH=/usr/local/java/whatever
	# export CLASSPATH
```
```
	% setenv CLASSPATH /usr/local/java/whatever
```
If that works, and it may take some experimentation to get the CLASSPATH right, add the line you typed in step 3 above, either to autoexec.bat or to the initialization file or preferences list for your Java compiler. Don Brutzman has some more information on setting up to compile and run Java at the Naval Postgraduate School.
When I run a Java Script, I get a NullPointerException.
First of all, look in your Java console, if your web browser has one. Determine what the Java Virtual Machine (JVM) or Java runtime is telling you isn't there. If the class or object that it can't find really is there, there are two possible explanations:
1. The planets are misaligned or you've been the victim of a stray cosmic ray. Hit the Reload button (shift-Reload is alleged to tell Netscape "No, seriously, I really mean reload") and try again.
2. Something essential hasn't loaded yet. The following is the Only True Way to initialize. Never, never assume that either the browser or any of the nodes in your scene is loaded. Use this code from Justin Couch:
```
for(int i = 0; i<SOME_NUMBER; i++)
{
     Browser b = Browser.getBrowser();

     if(b ==  null)
         sleep(SOME_TIME_VALUE)
     else
         break;
}
```
  I've seen lots of people use 5 for SOME_NUMBER and 500 for SOME_TIME_VALUE. Others do it as follows:
```
for(int i = 0; i<SOME_NUMBER; i++)
{
     Browser b = Browser.getBrowser();

     if(b !=  null)
         break;

     try {
         Thread.sleep(SOME_TIME_VALUE);
     }
     catch(InterruptedException e)
     {  // empty action
     }    
}
```
  Justin notes that you may have to repeat this with getNode(). And I'll add that whenever you're getting null pointers that seem to tell you that objects aren't there yet, do a spin like either of the examples above. I've also found that moving the initialization of pointers out of the initialize() method into the function that's called by the script will work, particularly if the script depends on a user action, at which point we can safely assume that the world has loaded.
Justin Couch has reported that a different NullPointerException can occur with Netscape Communicator with the AWT patch installed. This appears to be a bug in Communicator, and the workaround is to remove any reference to the Netscape classes from the CLASSPATH.
I can't get the EAI to work on my browser.
First, make sure it's the EAI that's broken, not your code. The examples in Chris Marrin's EAI draft spec should all work. If some of them work and some of them don't, your browser doesn't support all of the EAI classes correctly. Ross Finlayson's EAI FAQ has a number of hints for getting the EAI working on your machine. And Michael Paulitsch's VRML Examples show a number of Java Script and EAI techniques, though it may be wise to use the spin technique shown in the previous FAQ if you get NullPointerExceptions.

A new symptom has shown up with the release version of Cosmo Player 2.1. The error message is "netscape.javascript.JSException: unable to reflect embed with index 0 - not loaded yet?" It used to be that you could have the Java classes for other browsers in your CLASSPATH and Cosmo Player would ignore them. That's no longer so, and you have to get rid of them. The easiest way is to rename the file or folder. For example, C:\Java\classes\current.zip is in my CLASSPATH; I rename it to foo.zip. Then when I want to use the other browser, I rename it back to current.zip.

Did I leave something out on one of these questions that you need to know? Let me know.

-- Bob Crispen
-- Saturday, March 4, 2000