According to SQL syntax of Oracle database, you can't resize the data files by using ALTER TABLESPACE except the tablespace was created as BIGFILE, but we know most of tablespaces are created as SMALLFILE. So if you need to resize a normal data file, you'd better to use ALTER DATABASE.
SQL> alter database datafile '/oracle/oradata/user01.dbf' resize 10 m;
For more information, you may refer to the Oracle official documentation: