FIX: NoClassDefFoundError When a Valid Class Definition Exists

• Microsoft Internet Explorer version 4.0 for Windows NT 4.0
• SDK for Java, version 2.0
• Microsoft Internet Explorer version 4.0 for Windows 95

The information in this article applies specifically to version 4.79.2252 of the Microsoft Virtual Machine for Java, which is included in the above products.

SYMPTOMS

A Java applet or program that attempts to load certain valid Java classes may fail with a NoClassDefFoundError exception.

If the applet is running inside Internet Explorer, there may be no visible symptoms, except that the applet does not run properly. If Java Logging is enabled in Internet Explorer, however, the file Javalog.txt file, created in the Java subdirectory of the Windows directory, contains a log of the exception, and a call stack. Here is a typical example of the exception:

   java.lang.NoClassDefFoundError: COM/objectspace/jgl/HashMap

CAUSE

The Microsoft Virtual Machine for Java verifies that the .class file that defines each Java class is valid before loading it. Version 4.79.2252 erroneously decides that certain .class files are not valid, and therefore, fails to load them. When it fails to find a valid definition for a class, the Virtual Machine throws a NoClassDefFoundError exception.

RESOLUTION

Download and install the current Virtual Machine from the following Web site:

   http://www.microsoft.com/java/vm/dl_vmsp2.htm

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been corrected in the Microsoft Virtual Machine for Java, version 4.79.2334.

MORE INFORMATION

One class that the Virtual Machine fails to validate is the HashMap class from ObjectSpace's JGL class library. It is possible to produce other .class files that the Virtual Machine will fail to validate using a Java compiler, including Microsoft's Visual J++ or SDK 2.0 for Java.

Steps to Reproduce Behavior

If you have JGL and SDK 2.0 for Java, the following program will exhibit this bug:

   import COM.objectspace.jgl.*;
   public class HashMapTest
   {
      public static void main (String args[])
      {
         HashMap    hm = new HashMap();
      }
   }

REFERENCES

JGL is manufactured by ObjectSpace, Inc., a vendor independent of Microsoft; we make no warranty, implied or otherwise, regarding this product's performance or reliability.

Further information about JGL can be found at the following Web site:

   http://www.objectspace.com/jgl/

   http://support.microsoft.com/support/visualj/
   http://support.microsoft.com/support/java/