How do I call a method from an extend Class in Java?

I have a general Class called "Message":

public abstract class Message {

    private int type;
    private String origin;
    private String destination;
    
    public Message(int type, String origin, String destination) {
        this.type = type;
        this.origin = origin;
        this.destination = destination;
    }

    public int getType() {
        return type;
    }

    public String getOrigin() {
        return origin;
    }

    public String getDestination() {
        return destination;
    }
    
}

Also I have 2 more classes that extend from that one. "Conffirmation Connection Message"

public class ConnectionConffirmationMessage extends Message{

    public ConnectionConffirmationMessage(int type, String origin, String destination) {
        super(type, origin, destination);
    }

}

and "Connection Message"

public class ConnectionMessage extends Message{
    
    User info;

    public ConnectionMessage(int type, String origin, String destination, User info) {
        super(type, origin, destination);
        this.info = info;
    }

    public User getInfo() {
        return info;
    }
    
}

My problem is that now when I want to ask for the info when the Connection Message arrives I can't. Because the general class "Message" doesn't have the method "getInfo()".

Message msg = (Message) fin.readObject();

Any idea of what can I do?

Also, I can't simply change the type because I have this in a while with a switch, so if another type of Message arrives I have to process it.

Solution

You can cast you message into the specific sub-type

Before Java 14

if (msg instanceof ConnectionMessage) {
   User user = ((ConnectionMessage) message).getInfo(); 
   // do something with the user
}

After Java 14

if (msg instanceof ConnectionMessage connectionMessage) { 
    User user = connectionMessage.getInfo(); 
    // do something with the user
}

In this way, you will call the correct method.