I have the following code:
interface Entity {
}
class Student implements Entity{
}
class Course implements Entity{
}
interface BaseRepository {
public void save(Entity entiy);
}
class StudentRepository implements BaseRepository {
@Override
public void save(Student student) {
// student validation code
// save the entity
}
}
class CourseRepository implements BaseRepository {
@Override
public void save(Course course) {
// course validation code
// save the entity
}
}
When I try to compile it, gives me the following error:
StudentRepository is not abstract and does not override abstract method save(Entity) in BaseRepository
Doesn’t java accept a ‘Base’ class as an argument? What is the reason?
Is there any alternate way to write the code?
>Solution :
An overriding method must:
- have the exact same name
- have the exact same argument types; sub types won’t work!
- have a visibility that is the same or broader (so protected -> public is allowed, protected -> private isn’t)
- have a return type that is the same or a sub type
You’re violating the second rule here. Fortunately, you can use generics to fix this:
interface BaseRepository<E extends Entity> {
public void save(E entiy);
}
class StudentRepository implements BaseRepository<Student> {
@Override
public void save(Student student) {
// student validation code
// save the entity
}
}
class CourseRepository implements BaseRepository<Course> {
@Override
public void save(Course course) {
// course validation code
// save the entity
}
}
Now, the method that a BaseRepository<Student> should override is not public void save(Entity) but public void save(Student). Similarly, the method that a BaseRepository<Course> should override is not public void save(Entity) but public void save(Course).