code: void removeExtent(String classname)
      {
          synchronized (extentTable)
          {
              // returns the super class for given extent class name
              ClassDescriptor cld = (ClassDescriptor) extentTable.remove(classname);
              if(cld != null && m_topLevelClassTable != null)
              {
                  Class extClass = null;
                  try
                  {
                      extClass = ClassHelper.getClass(classname);
                  }
                  catch (ClassNotFoundException e)
                  {
                      // Should not happen
                      throw new MetadataException("Can't instantiate class object for needed extent remove", e);
                  }
                  // remove extent from super class descriptor
                  cld.removeExtentClass(classname);
                  m_topLevelClassTable.remove(extClass);
                  // clear map with first concrete classes, because the removed
                  // extent could be such a first found concrete class
                  m_firstConcreteClassMap = null;
              }
          }
      }
docs: Remove a pair of extent/classdescriptor from the extentTable.
  @param classname the name of the extent itself