Possible compiler bug

[Stefan Reich]

Hmm... so you're saying all the fields in a base class lose their type
parameters when I inherit from the raw base class? That's quite surprising
actually.

On Tue, 22 Oct 2019 at 13:16, Maurizio Cimadamore <
maurizio.cimadamore at oracle.com> wrote:

> The problem is that Derived.Inner extends Base.Inner - which is a raw type.
>
> Because of that, Derived.Inner does not inherit 'map' with type
> Map<Integer, Referenced> as you expect, but instead it inherits it raw
> (Map). Hence the error.
>
> To fix, you need to replace the extends clause of Derived.Inner to say
> "extends Base<Derived.Inner>.Inner"
>
> Maurizio
> On 22/10/2019 12:11, Stefan Reich wrote:
>
> Hi, ok, the class relationships in this example are bit convoluted (I have
> them for a reason in the original source code), but I still don't see why
> it would fail to compile.
>
> import java.util.Map;
> class Referenced {
> }
> class Base<A extends Base.Inner> {
>
>     class Inner {
>         Map<Integer, Referenced> map;
>
>         void bla() {
>             Referenced r = map.get(0);
>         }
>     }
> }
> class Derived extends Base<Derived.Inner> {
>     class Inner extends Base.Inner {
>         void bla() {
>             Referenced r = map.get(0);
>         }
>     }
> }
>
> The error message is:
>
> Referenced.java:20: error: incompatible types: Object cannot be converted
> to Referenced
>             Referenced r = map.get(0);
>
> Why does the map suddenly lose its type parameters?
>
> Many greetings,
> Stefan
>
> --
> Stefan Reich
> BotCompany.de // Java-based operating systems
>
>

-- 
Stefan Reich
BotCompany.de // Java-based operating systems
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