To begin connecting to a data source, you first need to instantiate
an object of your jdbc  driver. This essentially requires only one
line of code, a command to the DriverManager, telling the Java
Virtual Machine to load the bytecode of your driver  into memory,
where its methods will be available to your program. The String
parameter below is the fully qualified class name of the driver you
are using for your platform combination:

Class.forName("org.gjt.mm.mysql.Driver").newInstance();


Type of driver: JDBC-ODBC Bridge, Native-API, JDBC-Net, Native
Protocol
jdbc-odbc bridge :two step process.In client side we must install
ODBC.
Native-API:This is accessed via the Java Native Interface (JNI).
JDBC-Net :Three tiers connection required
Native Protocol : Every databse required own database.This is costly