Calling Field.type() which causes a JDWP ClassLoader.VisibleClasses
command to be sent, seems to cause a following VirtualMachine.allClasses()
call to return classes that are not prepared, as in the following example code:

 private void foo(VirtualMachine vm)
  {
    String margin "[GUS: ";
    System.err.println(margin+".................................................");
    vm.setDebugTraceMode(VirtualMachine.TRACE_ALL);
    try
    {
      for (Iterator it = vm.classesByName("gus.classloader.PolicyClassLoader").iterator(); it.hasNext(); )
      {
        ReferenceType rt = (ReferenceType)it.next();
        System.err.println(margin+"before rt.fieldByName");
        Field field = rt.fieldByName("parent");
        System.err.println(margin+"after rt.fieldByName");
        System.err.println(margin+"before field.type");
        Type type = field.type(); // This causes JDWP.ClassLoaderReference.VisibleClasses
        System.err.println(margin+"after field.type");
      }

      for (Iterator it = vm.allClasses().iterator(); it.hasNext(); )
      {
        ReferenceType rt = (ReferenceType)it.next();
        if (! rt.isPrepared())
        {
          System.err.println(margin+"rt.name(): " + rt.name());
          System.err.println(margin+"rt.isPrepared(): " + rt.isPrepared());
          System.err.println(margin+"rt.isInitialized(): " + rt.isInitialized());
          System.err.println(margin+"rt.isVerified(): " + rt.isVerified());
          System.err.println(margin+"rt.failedToInitialize(): " + rt.failedToInitialize());
          System.err.println(margin+"");
          ObjectReference or = null;
          try
          {
            or = rt.classObject();
            System.err.println(margin+"rt.classObject(): " + or);
          }
          catch (Exception e)
          {
            System.err.println(margin+"rt.classObject() threw " + e);
          }
          try
          {
            if (or != null)
              System.err.println(margin+"or.isCollected(): " + or.isCollected());
          }
          catch (Exception e)
          {
            System.err.println(margin+"or.isCollected() threw " + e);
          }
        }
      }
    }
    catch (Exception e)
    {
      e.printStackTrace();
    }
    vm.setDebugTraceMode(VirtualMachine.TRACE_NONE);
  }