Java warns that a casting is unchecked for generics hierarchy

Question

If I define the following types for a class:

class SomeClass<A extends InterfaceA, B extends InterfaceB, C extends B>

While InterfaceB extends InterfaceA. B also extends A but there I can’t declare that.

When casting an object of type C to any of [ B, InterfaceA, InterfaceB ], there isn't any warning (as expected).

But when casting C to A an unchecked cast warning raises. Why?

score 2 · Accepted Answer · answered Feb 01 '18 at 15:13

2

Because A is not in C's inheritance chain.

 InterfaceA
 /        \
A      InterfaceB
       /
      B
     /
    C

answered Feb 01 '18 at 15:13

Dave Drake

obviously, I was so into this issue that I didn't notice. My real problem is that I can't do something like that: `C extends B&A`. Thanks anyway – Noam Feb 01 '18 at 15:22

Linora · Answer 2 · 2018-05-08T12:13:11.423

1

Because C extends B, which implements InterfaceB, which in turn extends InterfaceA. C doesn't extend A.

edited May 08 '18 at 12:13

answered Feb 01 '18 at 15:14

Linora

2 Answers2