How to make method generic when using inheritance in Java?

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I have class Employee and 3 classes that extends Employee class. I also have EmployeeService interface where i want to have only one save method to handle saving each type of Employee. So i assumed that it could be solved using generics. This is what i tried in EmployeeService interface:

public interface EmployeeService {
<SubRequestT extends  Employee>EmployeeResponse save(SubRequestT requestT);
}

And class that provide implementation:

@Service
public class EmployeeServiceImpl implements EmployeeService {

// So here in argument i want to have to put any kind of Employee, for example:
@Override
public EmployeeResponse save(OfficeEmployee requestT) {
// Logic for saving employee
    return null;
}
}

But when i changed from Employee type to any other, for example OfficeEmployee who is extending from Employee, complier is giving me an error. What is best way to solve this?

inheritance generics java
1 Answers

With "method generics" I (me & compiler) also struggle, but with "type generics" we can do that!

Assuming:

class Foo {/*...*/}

class Bar extends Foo {}

class Baz extends Foo {}

// extending your question to two generic parameters:
class FooResult {}

class BarResult extends FooResult {}

class BazResult extends FooResult {}

When we define our interface like:

interface FooI<I extends Foo, R extends FooResult> { //or with even more (fixed size) "generic parameters"
  R save(I request);
}

We can override it like:

class BarImpl implements FooI<Bar, BarResult> {
  @Override
  public BarResult save(Bar bar) {
    // ...
    return ...;
  }
}

class BazImpl implements FooI<Baz, BazResult> {
  @Override
  public BazResult save(Baz baz) {
    // ...
    return ...;
  }
}
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