JDBC Connection refused - Mailing list pgsql-interfaces

Hi,

I created a database using createdb and it got created correctly.
However, I'm having trouble connecting to it with JDBC.  I named the
database "mydb" and the url I'm using in JDBC to connect is
"jdbc:postgresql:mydb".  I'm getting

java.sql.SQLException: Connection failed: java.net.ConnectException:
Connection refused

at runtime.  What causes this and how do I fix it?

Thanks,
Rich