Exception occured when connecting java to oracle 10g

My code is as below.

java.sql.DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
java.sql.Connection con=DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:xe", "ims", "_ims");

The exception occurs at second line which is given below.

java.sql.SQLException: Listener refused the connection with the following error:
ORA-12505, TNS:listener does not currently know of SID given in connect descriptor
The Connection descriptor used by the client was:
localhost:1521:xe"

What does exception means? Whats wrong in my code?

Edit by Girish

the listener.ora file :

SID_LIST_LISTENER =
  (SID_LIST =
    (SID_DESC =
      (SID_NAME = PLSExtProc)
      (ORACLE_HOME = C:\oraclexe\app\oracle\product\10.2.0\server)
      (PROGRAM = extproc)
    )
    (SID_DESC =
      (SID_NAME = CLRExtProc)
      (ORACLE_HOME = C:\oraclexe\app\oracle\product\10.2.0\server)
      (PROGRAM = extproc)
    )
  )

LISTENER =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC_FOR_XE))
      (ADDRESS = (PROTOCOL = TCP)(HOST = Girish-PC)(PORT = 1521))
    )
  )

DEFAULT_SERVICE_LISTENER = (XE)

The tnsnames.ora file :

XE =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = Girish-PC)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = XE)
    )
  )

EXTPROC_CONNECTION_DATA =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC_FOR_XE))
    )
    (CONNECT_DATA =
      (SID = PLSExtProc)
      (PRESENTATION = RO)
    )
  )

ORACLR_CONNECTION_DATA = 
  (DESCRIPTION = 
    (ADDRESS_LIST = 
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC_FOR_XE)) 
    ) 
    (CONNECT_DATA = 
      (SID = CLRExtProc) 
      (PRESENTATION = RO) 
    ) 
  ) 

In above, both tnsnames.ora and listener.ora file's contents is given.