public static GenericUDAFEvaluator getGenericUDAFEvaluator(String aggName,
      List<ExprNodeDesc> aggParameters, ASTNode aggTree,
      boolean isDistinct, boolean isAllColumns)
      throws SemanticException {
    return getGenericUDAFEvaluator2(aggName, getWritableObjectInspector(aggParameters),
        aggTree, isDistinct, isAllColumns);
  }
Returns the GenericUDAFEvaluator for the aggregation. This is called once
for each GroupBy aggregation.
ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java