private void registerDuplicateFunction(String name, SqlOperator calciteFn, HiveToken hiveToken) {
      hiveToCalcite.put(name, calciteFn);
      if (hiveToken != null) {
        calciteToHiveToken.put(calciteFn, hiveToken);
      }
    }
This class is used to build immutable hashmaps in the static block above.
ql/src/java/org/apache/hadoop/hive/ql/optimizer/calcite/translator/SqlFunctionConverter.java