Re: Basic stupidity Java generics

From:

Sabine Dinis Blochberger <no.spam@here.invalid>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 05 Sep 2008 09:25:54 +0100

Message-ID:

<dNCdnVh_0dWOcF3VnZ2dnUVZ8rCdnZ2d@novis.pt>

pjvleeuwen@gmail.com wrote:

Damn! sorry, I found the problem. I spend two hours before posting the
question and I found the answer just minutes after the posting:
This is not correct: IContainer<IThing> var = new Container<Thing>();
It needs to be: IContainer<? extends IThing> var = new
Container<Thing>();

Again, sorry, and thanks for reading.

No problem, but thanks for posting back with the solution.

In the future, please do not top-post.

Cheers,
Paul

On 4 sep, 21:58, "pjvleeu...@gmail.com" <pjvleeu...@gmail.com> wrote:

Hi all,
Probably I am doing something very twisted, but I keep getting an
"incompatible types" compile error and I don't know why. I brought it
back to the very simple script below. Could somebody please explain
me, why is this incorrect, it seems perfectly logical to me... :(
This is a big problem for me, because I want to hide all
implementation behind interfaces, and I need the return type
IContainer<Ithing> to be compatible with Container<Thing>. Apparently
it isn't.
Anyone? Many things for any help!
Cheers,
Paul

public class Test {
        public interface IThing {
        }
        public interface IContainer<TYPE extends IThing> {
        }
        public class Thing implements IThing {
        }
        public class Container<TYPE extends Thing> implements
IContainer<TYPE> {
        }
        public Test() {
                IContainer<IThing> var = new Container<Thing>();
        }
        public static void main(String[] args) {
                new Test();
    }

}

$ javac Test.java
Test.java:23: incompatible types
found : Test.Container<Test.Thing>
required: Test.IContainer<Test.IThing>
                IContainer<IThing> var = new Container<Thing>();
                                         ^
1 error

--
Sabine Dinis Blochberger

Op3racional
www.op3racional.eu