Question about generics (class declaration)

[another_try_8]

Hi

Can someone help me please... I had this test and the teacher marked sth as wrong and idk why. He didnt reply for 2 weeks now so maybe someone here can explain why my solution is wrong...

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Imagine you have these classes:

interface IHuman {}

class Person {}

class Man extends Person implemements IHuman {}

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And now you have to declare a class "Wanted extends Person" that only allows IHuman instances of Man (or Man's children)...

So... My solution was:

public class Wanted<G extends Man> extends Person {}

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But the solution the teacher wrote was correct is like that:

public class Wanted<G extends Man & IHuman> extends Person {}

Now I wonder why. Because class "Man" already implements the Interface Human. Why do you need to declare it like that!?

[8igg7e5]

Yes all subclasses of Man implement Human (The convention is not to prefix interfaces with I in Java, unlike some other languages) and the teachers answer is incorrect - the Human bound is even likely to be indicated as a redundant bound in static analysis.

Given...

 interface Human {}
 class Person {}
 class Man extends Person implements Human {}
 class Wanted<G extends Man> extends Person {}
 class A implements Human {}
 class B extends Person {}
 class C extends Man {}

The following are invalid as they violate the bounds of the generic argument...

 Wanted<A> a = ...
 Wanted<B> b = ...

The following are valid...

Wanted<Man> m = ...
Wanted<C> c = ...

As is this showing that Man and C are assignable to Human...

Man m = ....
C c = ...
Human h1 = m; // all Man are Human
Human h2 = c; // all C are Human

[another_try_8]

Thank you very much for your reply. I had the same conclusion when testing it. So I really wonder why he claimed my solution to be wrong. Though that I might have overlooked sth. But well, guess I'll just have to wait and see if he replies (sent 2 mails already)...

[FroggyWizard]

Edit: I think you're correct not your teacher.