Using JDBC when server name contains a backslash (localhostTESTDATA)

thanks for taking the time to read this. I'm completely stumped by what is probably a simple thing. I am trying to make a connection to my SQL database, the following tends to work:

String url = "jdbc:jtds:sqlserver://10.0.100.200;DatabaseName=master;user=sa;password=";

However when my name contains a backslash, for example "localhostTESTDATA I cannot seem to get it working, I am getting

"java.sql.SQLException: Unknown server host name 'localhostTESTDATA'."

when I use the following:

String url = "jdbc:jtds:sqlserver://localhost\TESTDATA;DatabaseName=master;user=sa;password=";

Thanks