泛型“方法不会覆盖其超类中的任何方法”

Question

I have created an interface with a generic method, when overriding this method in my class that implements this interface the compiler complains saying "method does not override method from its superclass". This problem occur only when i added a generic param to my abstract method.

I created an interface whith one generic method and a Class that implements this interface.

package me.work.rest;
public interface RestControllerFacade<T> {
    <P, R, E extends Throwable> R retrieveCollectionResources(P p) throws E ;
}

@RestController
@RequestMapping("api/v1/Users")
public class UserResource implements RestControllerFacade<User> {
    @GetMapping( produces = MediaType.APPLICATION_JSON_VALUE )
    @Override
    public ResponseEntity<Page<User>> retrieveCollectionResources(Pageable 
    pageable) throws ResourceNotFoundException {
        code...
        return ...;
    }
}

The compiler says "method does not override method from its superclass". By the way this code is working for me :

package me.work.rest;
public interface RestControllerFacade<T> {
    <R, E extends Throwable> R retrieveCollectionResources() throws E ;
}

@RestController
@RequestMapping("api/v1/Users")
public class UserResource implements RestControllerFacade<User> { 
@GetMapping( produces = MediaType.APPLICATION_JSON_VALUE )
    @Override
    public ResponseEntity<Page<User>> retrieveCollectionResources() throws ResourceNotFoundException {
        code...
        return ...;
    }
}

Only when adding the P param to the method the compiler complains! Any help is appreciated. Thank you.

Answer 1

If you want that to be a valid override, then P , R , and E need to be generics on the interface , not the method. It has to be

public interface RestControllerFacade<P, R, E extends Exception, T> {
    R retrieveCollectionResources(P p) throws E ;
}

@RestController
@RequestMapping("api/v1/Users")
public class UserResource implements 
        RestControllerFacade<
           Pageable, 
           ResponseEntity<Page<User>>, 
           ResourceNotFoundException, 
           User> {
    @GetMapping( produces = MediaType.APPLICATION_JSON_VALUE )
    @Override
    public ResponseEntity<Page<User>> retrieveCollectionResources(Pageable 
    pageable) throws ResourceNotFoundException {
        code...
        return ...;
    }
}

The way you have written it, any RestControllerFacade has to be able to work for any P , R , and E , not just some particular combination.