Java Generics <this??>

Question

Is there any way you could use a type of the class you're in for a generic argument? for example I have this class ServiceNode

public final class ServiceNode<S extends NetworkService> {

    private final S service;
    private final Client client;
    private Object attachment;

    public ServiceNode(S service, Client client) {
        this (service, client, null);
    }

    public ServiceNode(S service, Client client, Object attachment) {
        this.service = service;
        this.client = client;
        this.attachment = attachment;
    }

    public S service() {
        return service;
    }

....

}

which is a part of the abstract class NetworkService

public abstract class NetworkService {

    private final Set<ServiceNode<?>> registeredNodes = new HashSet<>();

    public final void register(ServiceNode<?> node) {
        registeredNodes.add(node);
    }

    ...

}

So basically is there anyway to remove the wildcard argument from ServiceNode in the NetworkService class and replace it with whatever type the class is extending NetworkService

Answer 1

Genericise your base class thus:

public abstract class NetworkService<T extends NetworkService<T>> {

    private final Set<ServiceNode<T>> registeredNodes;

    ...
}

and then extend from it thus:

public class MyNetworkService extends NetworkService<MyNetworkService> {
    ...
}

Google for curiously recurring generic pattern.