在Scala中使用抽象成员类实现抽象的通用Java类

Question

I'm trying to implement an abstract, generic Java class in Scala, and I'm getting an error of the form

object creation impossible, since method B in class A of type (x$1: A<Concrete1, Concrete2>#C)Unit is not defined

The library classes that I'm implementing look like this:

public abstract class A<T, U> {
    public void B(C);

    public abstract class C {
        // elided
    }
}

and I want to implement an A to hand back to the library (which will call B , supplying a C ). In Java, I can do:

new A<Concrete1, Concrete2>() {
    @Override
    public void B(C c) {
        // implementation
    }
}

In Scala, I'm trying

new A[Concrete1, Concrete2] {
    def B(c: C): Unit = {
        // implementation
    }
}

and I get the error message at the top. Using override , the compiler complains that method B overrides nothing . It seems that the Scala type system isn't recognizing the C I pass in as an A<Concrete1, Concrete2>#C , but I'm not sure what type it does think it is.

I've tried specifying self: A[Concrete1, Concrete2] => , as well as a self-type on C : def B(c: self.C , but neither solves the problem. I also tried def B(c: A[Concrete1, Concrete2].C) , but this raises a syntax error.

Any suggestions?

Answer 1

Solved: def B(c: A[Concrete1, Concrete2]#C): Unit . Needed the generic type information for this to be a valid override, but I wasn't aware of the # operator.