Question

implements GenericObserver<DataService, Tools>, GenericObserver<MobileService, Tools>

cannot be implemented more than once with different arguments.

This is my interface:

public interface GenericObserver<S, D> {

    void update(S sender, D data);
}

What can I do? I need DataService and MobileService.

I try to use generic T instead of DataService and MobileService but I get an error that T does not exist.

Answer 1

One possibility:

abstract class Service {}

class DataService extends Service {}

class MobileService extends Service {}

class Foo implements GenericObserver<Service, Tools> {
    void update(Service sender, Tools data) {
        if (sender instanceOf DataService) {
            // do something
        } else if (sender instanceOf MobileService) {
            // do something else
        } else {
            // throw some notImplemented exception
        }
    }
}

The Visitor pattern is another possibility (GenericObserver being the visitable).