Strange generics error

[David Nemeskey]

Hi,

I have come across a strange error while using generics. I want to overwrite outerMethod() in the subclasses, and I want to use the type safety provided by generics. There is a sample static subclass called aptly sample. Is there a way to achieve the differently?

public class OuterClass<I, O> {
    public void outerMethod(InnerClass<I, O> inner) {
    }
 
    protected class InnerClass<I, O> {
        protected I input;
        protected O output;
        
        public void innerMethod() {
            outerMethod(this);
        }
    }
 
    public static OuterClass<Integer, Integer[]> sample =
            new OuterClass<Integer, Integer[]>() {
        public void outerMethod(InnerClass inner) {
            for (Integer i : inner.output) {
                System.out.println(i);
            }
        }
    };
}

The error message I get is a bit absurd... and not helpful at all.

OuterClass.java:12: outerMethod(suncertify.gui.OuterClass<I,O>.InnerClass<I,O> :wink:  in suncertify.gui.OuterClass<I,O> cannot be applied to (suncertify.gui.OuterClass<I,O>.InnerClass<I,O> :wink: 

I can change the code, and that solves the problem, but isn't there a better solution?

public class OuterClass<I, O> {
    public void outerMethod(InnerClass inner) {
    }
 
    protected class InnerClass {
        protected I input;
        protected O output;
        
        public void innerMethod() {
            outerMethod(this);
        }
    }
}

[Bupjae Lee]

public class OuterClass<I, O> {
    public void outerMethod(InnerClass inner) {
    }
 
    protected class InnerClass {
        protected I input;
        protected O output;
 
        public void innerMethod() {
            outerMethod(this);
        }
    }
}

That is correct answer.

If you declare InnerClass<I, O> instead of InnerClass, something like OuterClass<Integer, Integer[]>.InnerClass<String, String[]> is acceptable.

It means that type parameter I, O in OuterClass is different from type parameter I, O in InnerClass, and the compiler complains about this fact.

[Paul Clapham]

Originally posted by David Nemeskey:
I can change the code, and that solves the problem, but isn't there a better solution?

Hard to say. What don't you like about that solution? To me it looks better than the original version.