CODEWITHSUNDEEP
javagenerics
sam
sam

Reputation: 63

What type parameters would an innerclass and interface have in the following situation?

Suppose we have a generic class that implements a generic interface like this

GenericClass.java

public class GenericClass<T> implements GenericInterface<T> {

    private class AnotherClass<T> {
        T aVariable;
    }

    @Override
    public T aMethod() {
        return null;
    }
}

GenericInterface.java

public interface GenericInterface<T> {
    T aMethod();
}

What would be the type parameter passed on in the interface? Also, what would be the type parameter passed to the nested class inside GenericClass.

Upvotes: 0

Views: 114

Answers (2)

akuzminykh
akuzminykh

Reputation: 4723

I'll take your comment as the actual question:

If I create a new instance of GenericClass like this: new GenericClass then will the interface it implements also be GenericInterface and will the inner class als be AnotherClass

Yes, it's gonna be GenericInterface<Integer>. No, it's not gonna be AnotherClass<Integer>.

class GenericClass<T> introduces a type-parameter T that can be used e.g. with a generic interface like you do. Now be careful: class AnotherClass<T> that is nested within GenericClass introduces another type-parameter T that hides the one that GenericClass has introduced.

If you want AnotherClass to use T of GenericClass, then simply skip the <T> for AnotherClass.

Upvotes: 4

Andreas
Andreas

Reputation: 159086

What would be the type parameter passed on in the interface?

The one given on the GenericClass declaration.

E.g. if you have new GenericClass<Integer>(), then the interface would be GenericInterface<Integer>.

What would be the type parameter passed to the nested class inside GenericClass.

The one given on the AnotherClass declaration.

E.g. if you have new AnotherClass<String>(), then aVariable would have type String. That is true even if the outer class is a GenericClass<Integer>.

If you use a good IDE, then it would likely tell you that the T for AnotherClass is hiding the T for GenericClass.

Upvotes: 1

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