@Override public Object evaluate(DeferredObject[] arguments) throws HiveException {
    Object o0 = arguments[1].get();
    if (o0 == null) {
      return null;
    }
    return convert(o0);
  }
@param arguments
 0. const int, value of a HiveParser_IdentifiersParser constant which represents a TOK_[TYPE]
 1. expression to convert
 2. constant string, format pattern
 3. (optional) constant int, output char/varchar length
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDFCastFormat.java