public static GenericUDAFResolver getGenericUDAFResolver(String functionName)
      throws SemanticException {
    LOG.debug("Looking up GenericUDAF: {}", functionName);
    FunctionInfo finfo = getFunctionInfo(functionName);
    if (finfo == null) {
      return null;
    }
    GenericUDAFResolver result = finfo.getGenericUDAFResolver();
    return result;
  }
Get the GenericUDAF evaluator for the name and argumentClasses.

@param name
         the name of the UDAF
@param argumentOIs
@param isDistinct
@param isAllColumns
@return The UDAF evaluator
ql/src/java/org/apache/hadoop/hive/ql/exec/FunctionRegistry.java