The JDBC  DriverManager is a clas....It loads the JDBC 
driver needed to access a particular data source, locates 
and logs on to the database and returns a Connection 
object.

in JDBC except DriverManager ang SQLException remaaining 
all are interfaces.

DriverManager is a Class as part of javax.sql.*; package.The
purpose of DriverManager is to register the JDBC Driver and
to get the Connection Object
--->DriverManager.registerDriver(new
Oracle.jdbc.driver.OracleDriver());
--->Connection
con=DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:xe","scott","tiger");

DriverManager is a class that present in java.sql package
which is used to connect the our application with database.
that is DriverManager containing getConnection() method 
that return Connection object

DriverManager is a class. By using the static method
(registerDriver) of this class you can register the 
different venders JDBC drivers. Also by using getConncetion 
method you can connect to the database which is registered, 
it returns the object ref of Connection interface.