How to reference a subclass as a type parameter?

Question

Is there a way to use a subclass of the current class as a type parameter for a generic class ?

I'm not very sure how to expose my problem so I'll go with an example :

Example

My Connection object is responsible for sending and receiving a certain type of (subclass of) Message over the network (only reproducing the relevant parts here) :

public class Connection<M extends Message> {
    public void send(M mes) {
        ...
    }
}

My Message object is an abstract class superclassing all kinds of messages sent over the network.

public abstract class Message {
    private transient Connection<?> conn;

    public void send() {
        this.conn.send(this);
    }
}

Of course, I have several subclasses of Message.

Problem

My problem comes from the Connection<?> conn property of Message : in it's current state eclipse tells me that

The method send(capture#7-of ?) in the type Connection< capture#7-of ?> is not applicable for the arguments (Message)

What type parameter should I use for Connection so that it is compatible with any subclass of Message ?

What I tried

I tried declaring Message as :

public abstract class Message<M extends Message<M>> {
    private transient Connection<M> conn;
    ...
}

And then I would have :

public class MessageA extends Message<MessageA> {
    ...
}

as a subclass.

But this is a big hassle (I have a lot of generic classes using subclasses of Message as type parameters) and it doesn't seem to be the proper way to handle it.

Answer 1

Use Connection<Message>:

public abstract class Message {
    private transient Connection<Message> conn;
    ...
}