Please see the cases.
 
The account information are like these,
username       password
SYS                 ADMIN
SRDEMO       ORACLE
 
The results to try,
command                                                        login result
sqlplus sys/admin@orcl                              success
sqlplus SYS/ADMIN@orcl                         success
sqlplus srdemo/oracle@orcl                        fail
sqlplus SRDEMO/ORACLE@ORCL          success
 
Please notice that it is the same case you are connecting with JDBC driver.