@Override public String getDisplayString(String[] children) {
    return getStandardDisplayString(getFuncName(), children);
  }
Evaluate the GenericUDF with the arguments.

@param arguments timestamp and interval.

@return The truncated timestamp to the beginning of tumbled window interval.
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDFTumbledWindow.java