Java Generics Extends Class Parameter

Question

I received an error and I have this structure in my program

public interface Shapes{
//methods here
}

public class ShapeAction implements          


        

Answer 1

Have you tried this?

public class Circle extends ShapeAction{
//Some methods here
}

There is no way the compiler can tell what the T argument means in extends ShapeAction unless you define it first.

Eventually, when you use a reference to a Circle, you will have to provide a type argument for T, which will be cascaded to all other appearances of this type.

Circle myInt;

Will cause the compiler to interpret the code as:

public class Circle extends ShapeAction{
    //Some methods here
}

And so on, for the rest of the class hierarchy.

As such, if you do not define the type T in the class Circle. There wouldn't be a way for the compiler to tell the parameterized type of ShapeAction and this is most likely the source of the problem here.