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.

Ejb object is a server-side object,and it conatins business
methods,that is why we need to call ejb object as a business
component.

Ejb objects are used to access the Business logic methods 
defined by the user in the bean. client gets the reference 
of the object using JNDI, and cast the object as the 
HomeObject and access the methods in the bean.

EjbObject is an object which implements our component 
interface.The container creats it when we call create 
method on home stub.It contains business methods.It is a 
beans body guard.

EJB object implements Component Interface. It is created by 
the container when create() method is called by the Home 
interface. EJB object contains the business methods present 
in the bean class. Hence client request invokes the 
business method on bean via the EJB object.