Re: [TriJug] Generics Help

The following is not as type safe as you are aiming for, but the warning is
gone.

public class CO
{
    static Cont<CO> getCont(CO c)
    {
        if (c instanceof C1)
            return new D1();
        if (c instanceof C2)
            return new D2();
        throw new Error();
    }

    static
    {
        CO c = new C1(); // or C2
        Cont<CO> cont = getCont(c);
        cont.add(c);
    }
}
class C1 extends CO
{//
}
class C2 extends CO
{//
}
class Cont<T extends CO> {
    void add(T t) {//
        }
}
class D1 extends Cont<CO>
{//
}
class D2 extends Cont<CO>
{//
}


On 3/15/06, cebmailbox-trijug-/[email protected] <cebmailbox-trijug-/[email protected]> wrote:
>
> Anyone know the answer?
>
> Given the following code:
>
> A base class:
>    class C0 {...}
>
> 2 subclasses:
>     class C1 extends C0 {...}
>     class C2 extends C0 {...}
>
> A generic container to hold either:
>     class Cont<T extends C0> {
>         void add(T t) {...}
>     }
>
> 2 specialized containers:
>     class D1 extends Cont<C1> {...}
>     class D2 extends Cont<C2> {...}
>
> *Crucially now* a static method returns the matching container:
>     static Cont getCont(C0 c) {
>         if (c insta! nceof C1)  return new D1();
>         if (c instanceof C2)  return new D2();
>     }
>
> Expected usage:
>     C0 c = new C1();  //or C2
>     getCont(c).add(c);
>
> But compiles with the warning:
>     Type safety: The method add(C0) belongs to the raw type Cont.
> References to generic type Cont<T> should be parameterized.
>
> The above is obviously contrived and there are probably other
> implementations that can get around the warning.  I could also suppress the
> warning.
>
> BUT as a learning exercise, I really want to know if there is any
> change that could be made to the signatures of the classes, the static
> method or the usage that would eliminate the warning.
>
> -Ch! ris
>
>
> _______________________________________________
> Juglist mailing list
> [email protected]
> http://trijug.org/mailman/listinfo/juglist_trijug.org
>
>
>

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