Wildcards to accept any type with interface

Question

I'm trying to use generics to accept any object that implements the Client interface, but I can't seem to get it right.

public interface Client {
  public void makeMove();
}

public MyClient implements Client {
  public MyClient(Server server) {
    server.connectClient(this);
  }
}

The error I get above is: The method connectClient(Class<? extends FanoronaClient>) in the type Server is not applicable for the arguments (GUIClient)

The server with generics:

public class Server {
  private Class<? extends Client> client_;

  public void connectClient(Class<? extends Client> client) {
    client_ = client;
    client_.makeMove(); // type error here
  }
}

And the error here is The method makeMove() is undefined for the type Class<capture#7-of ? extends Client> The method makeMove() is undefined for the type Class<capture#7-of ? extends Client>

What am I doing wrong?

Answer 1

You are trying to call a method on the class java.lang.Class , which doesn't exist. What you actually want is an implementation of your class/interface to be passed to your method.

Your connetClient method should look something like this instead:

public void connectClient(Client client) {
    client.makeMove(); // no more type error
}

Of course if you want to keep a reference to this in your class, you will have to change the _client member of your Server class to also be of type Client .

I don't think you want to be using generics at all in this example...

Answer 2

Try this code out :

public class Server {
      private Class<? extends Client> client_;

      public void connectClient(Class<? extends Client> client) {
        client_ = client;
        client.newInstance().makeMove(); // no error here 
      }
    }