Lake Access - Java Problem Diagnosis



Java Problems

This page might help you out if you are having trouble using our data visualization applets. An applet is a program, written in the Java programming language, that can be run from a web browser.

In theory, our applets will work on any computer with an Internet browser that supports Java version 1.1 or better. This includes Netscape and Internet Explorer browsers, versions 4 or higher.

That's the theory, but the reality is a little more complicated. Here's a little background on how Java is supposed to work:

Most computer programs are written in a format that (some) humans can understand. Then the programs are compiled, which means they are translated to a format that a computer understands. But a Mac can't understand a program that was compiled for a Windows computer, and a Windows computer can't understand a program that was compiled for Linux, etc...

Java programs are supposed to run anywhere. They do this by getting compiled to run on a make-believe computer: the Java Virtual Machine (or JVM). All of the different computer makers and Internet browser makers who want to be able to run Java programs just provide a JVM program that translates the JVM code to something that their particular computer/operating system/browser understands. If they did a good job of writing the JVM translator their system will be able to run the applet.

But, the various JVMs each have their own peculiar bugs.

We run our applets on all the JVMs we can get our hands on, and try to work around each problem that we find. But we can't test every combination -- if you come across something that this page doesn't cover please send us the details (access@nrri.umn.edu) and we'll try to fix it.

Which version of Java are you using?

Here is a small Java applet that will tell you:

You are not running Java. It is either not installed, or it is disabled. Follow the instructions below to get it running.

Interpreting the results:

If the applet reported that your Java Version is less than 1.1 :

You will need to use a different browser. For example, the JVM included with Netscape 3 only supports Java version 1.02. Our applets rely on some features that weren't introduced until later. They have been tested on Netscape and Internet Explorer browsers , versions 4 and higher.

If you see a message that starts out with "You are not running Java...." :

either -- Java is not installed on your browser:

On a Windows PC, Java is no longer included when you do the default installation of Internet Explorer.

If you are going to install IE5+, do a custom install and make sure to include the virtual machine. If you already have IE5+ and need to add Java support, follow the instructions for installing/updating Java given below.

Macintosh users who are using recent versions of Internet Explorer can install a Java plug-in -- see below.

or -- You need to enable Java:

Look for this option somewhere in the preferences settings of your browser. With Netscape 4 you will find this setting if you choose Edit >> Preferences from the menu, click on Advanced, and make a check beside the Enable Java choice.

With Internet Explorer, the Java settings are buried under Tools >> Internet Options >> Security >> Custom >> Microsoft VM. If Disable Java is selected, you will need to change it (our applets will run with the High Safety setting).

If the applet reported that your Java vendor was Netscape Communications Corporation and the Java version is between 1.1.0 and 1.1.3 --

Although it claims to be version 1.1, the JVM included with the Netscape 4.X browsers on the Mac and the early PC versions left out a number of features that are required to fully support v1.1 Java programs. We've managed to work around most of them, but you may find that you are unable to use the "Copy this Image" button to make a copy of the image generated by the Color Mapper and DxT applets.

If the applet reported that your Java vendor was Microsoft Corp and it reports your MS JVM build # is less than 3810 --

Build # 3805 is Microsoft's most recent (as of April 2003) version of the Java virtual machine that is used by Internet Explorer (version 4 or higher) on Windows computers. Even if you are running the latest version of Internet Explorer, you might be using an earlier version of the JVM. For example, if you upgraded to IE5 from IE4 the JVM would not get upgraded by default. Many people running IE5.5 are still using the JVM build # 2339 that came with their original IE4 installation. Since then, Microsoft has fixed a number of bugs, and filled some security holes that were found in the earlier builds.

We suggest that you install the latest JVM. We've worked around as many of the bugs found in their earlier JVMs as we could, but some remain. For example, if your VM build # is 2339, you might get an error message like this when you close your browser after running the DVTools applet:

IEXPLORE caused an invalid page fault in module MSJAVA.DLL at 0137:7c03da2e.

Updating your VM will take care of that problem, as well as improve the security of your computer. See the installing/updating Java section for details.

Installing / Updating Java

Windows users:

Netscape: Our applets should run on Netscape browsers starting with version 4, but some of the features will be disabled with the early 4.0x browsers. If you are using Netscape 3 you are out of luck -- you'll need to upgrade to a newer version.

Internet Explorer : Our applets should run on Internet Explorer starting with version 4, provided that you have the MS JVM installed. There are several ways to get the latest version. If you are running IE5 or higher, you can click on Tools >> Windows Update in the IE menu. If you then select Product Updates a list will be generated that describes the upgrades that are suggested for your system. One of the choices will be for the Virtual Machine (if you don't already have the most recent version installed). Select this item, and follow the instructions to install it.

Microsoft is removing their JVM from their products --you can go to http://www.microsoft.com/java/ for details.

Instead, you can use Sun's JVM in current versions of Internet Explorer.

Macintosh users:

Netscape: Our applets should run on Netscape browsers starting with version 4, but they have not yet been thoroughly tested. Let us know the details of any problems that you encounter -- send email to: access@nrri.umn.edu

Internet Explorer : Current releases of Internet Explorer for the Macintosh can be configured to use Apple's Mac OS Runtime for Java (MRJ). To do so:

Download and install the MRJ.

Open the current version of Internet Explorer

From the Edit menu select: Preferences... >> Web Browser >> Java >> Java Virtual Machine >> Apple MRJ >> OK.

Unix/Linux/etc.. users:

Netscape: Again, our applets should run on Netscape browsers starting with version 4, but they have not yet been thoroughly tested. Help us out -- send your reports to: access@nrri.umn.edu

We have found that the "Copy this Image" feature in DxT and the Color Mapper can take a long time on some Unix computers -- on a Windows PC the result is immediate. On a Solaris running Netscape (v4.73?) it took about a minute.

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