Java:How to override this generic method?
generics, java, overriding, type-erasure
Solution
My solution was to not override this at all but to create a service class that does the needed logic and leave repository untouched.
Problem
``` public <S extends T> List<S> save(Iterable<S> entities) { //... } ``` If I use following method to override ``` @Override public List<MyType> save(Iterable<MyType> structures) { List<MyType> result = new ArrayList<>(); //... return result; } ``` I get following error: ``` method does not override or implement a method from a supertype name clash: save(Iterable<MyType>) in MyTypeRepositoryImpl and <S>save(Iterable<S>) in SimpleJpaRepository have the same erasure, yet neither overrides the other where S,T are type-variables: S extends T declared in method <S>save(Iterable<S>) T extends Object declared in class SimpleJpaRepository ``` How can I solve this? I don't need the method to be generic and in fact it should not be. What I mean is that ``` @Override public <S extends MyType> List<S> save(Iterable<S> structures) { List<S> result = new ArrayList<>(); //... return result; } ``` Will not work as the method can create a new Object of MyType which is not "compatible" to List. How can I make this work? EDIT: For clarification. I'm trying to override the different save() methods of Spring data SimpleJpaRepository (which is extented by QuerydslJpaRepository) Class defintions: ``` public class MyTypeRepositoryImpl extends QueryDslJpaRepository<MyType, Long> implements MyTypeRepository @NoRepositoryBean public interface MyTypeRepository extends JpaRepository<MyType, Long>, QueryDslPredicateExecutor<MyType> ``` And this (from Spring Data) ``` public class QueryDslJpaRepository<T, ID extends Serializable> extends SimpleJpaRepository<T, ID> implements QueryDslPredicateExecutor<T> ``` EDIT 2: The method calls save(MyType entity) for each element and that method contains following logic: - entity has a field which is unique - get that fields value and check if entity with that value already exists - if yes, use that entity (call to entityManager.merge) -> does not work returns MyType not S - if no create a new one -> here new object is created. Does not work with generic type For 4. I can just set id = null and use the passed in object. That does not work for 3. So I'm very puzzled why this method has this signature. It makes it unusable for me and i don't get why I would save a subclass of T using Ts DAO. the save methods are the only ones with . All others just use T. I could just cast to S to make it compile but that seems ugly too...as any other type than T would lead to an exception.