This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
The braces are the escape syntax for stored procedures.
While using a PreparedStatement to call a stored procedure might work, it is risky because it might not. Or you could upgrade your driver and have it not work. It is better to use the intended CallableStatement subclass.