@Override
  public String getDisplayString(String[] children) {
    return getStandardDisplayString(getFuncName(), children);
  }
GenericUDFDateFormat.

converts a date/timestamp/string to a value of string in the format specified
by the java date format
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDFDateFormat.java