Question

I have some troubles with a method having a typed List parameter, inherited from another (typed) class.

Let’s keep it simple :

public class B<T> {
  public void test(List<Integer> i) {
  }
}

The B class has a useless generic T, and test() want an Integer List.

Now if I do :

public class A extends B {
  // don't compile
  @Override
  public void test(List<Integer> i) {
  }
}

I get a “The method test(List) of type A must override or implement a supertype method” error, that should not happen.

But removing the type of the list works… although it doesn’t depend on the class generic.

public class A extends B {
  // compile
  @Override
  public void test(List i) {

And also defining the useless generic below to use the typed list

public class A extends B<String> {
  // compile
  @Override
  public void test(List<Integer> i) {

So I’m clueless, the generic of B should have no influence on the type of the test() list. Does anyone have an idea of what’s happening?

Thanks

Answer 1

You’re extending the raw type of B, not the generic one. The raw one effectively does not have a test(List<Integer> i) method, but a test(List) method.

If you switch to raw types, all generics are replaced by raws, regardless of whether their type was filled in or not.

To do it properly, do

 public class A<T> extends B<T>

This will use the generic type B<T>, which includes the method you want to override.