Interface, Class, Object

Question

Hi all,
In the following code: factory is an object of type: progress.message.jclient.ConnectionFactory
Then the method: createConnection() returns Connection: a newly created connection>
javax.jms: Interface Connection:
A Connection object is a client's active connection to its JMS provider.
When we create a new object, the return value should be an instance of a class and not an interface; right?
So shouldn't Connection be a Class and not an Interface?
Like the method: readLine() in java.io: Class BufferedReader, returns an object of type: java.lang: Class String and not interface: String.
Sorry for confusion, I guess I'm missing a point here...
Any help is greatly appreciated.
public class Chat implements javax.jms.MessageListener
private javax.jms.Connection connect = null;
private void chatter( String broker, String username, String password)
// factory is an object of type: progress.message.jclient.ConnectionFactory
javax.jms.ConnectionFactory factory;
            factory = (new progress.message.jclient.ConnectionFactory (broker));
            connect = factory.createConnection (username, password);
}

Answer 1

Ok, every object is an instance of a class.
It is an instance of exactly this class, and certainly also of it's super classes - through the feature of inheritance.
Now when you have a reference to an interface, it always references a concrete object of a certain class. This class implements the interface, so you can forget about it's concret identity and just handle it as just any object implementing that interface.
So an object can also be an instance of an interface - if its class implements it.
Did you get it so far? (sorry, if not, I am not a native speaker)
So the createConnection method has the return type javax.jms.Connection which means that it can return any object of any class implementing this Interface. It does not list the concrete class because the underlying implementation class of any JMX vendor should be transparent to your code.
You understand?
I hope i could make it a little clearer.
regards
Sven