Does the return value of an abstract method can be of generic type

Question

the first part of my project is to construct an hypergraph

This is a quickly-drew UML diagram

The vertex class

    public abstract class Vertex <T>{

int vertexId ;
T vertexValue ;

public  abstract <T> T setVertexValue();

    }

The imageVertex class

   public class ImageVertex extends Vertex<Map<String, Instance>>{

@Override
public <T> T setVertexValue() {
    // TODO Auto-generated method stub
    return null;
}}

I has thought that Type will be inferred automatically as i define it for the imageVertex Map and later for tagVertex as String

had I wrongly used the generics?

Answer 1

You've redefined the type T on setVertexValue. Use this.

public abstract class Vertex <T>{

int vertexId ;
T vertexValue ;

public  abstract T setVertexValue();

}

It uses the generic properly

public class ImageVertex extends Vertex<Map<String, String>>
{

    @Override
    public Map<String, String> setVertexValue()
    {
        // TODO Auto-generated method stub
        return null;
    }

}

Answer 2

It seems that you are trying to write:

public abstract class Vertex<T> {

    int vertexId;
    T vertexValue;

    public abstract T setVertexValue(); // NOTE: no <T>
}

public class ImageVertex extends Vertex<Map<String, Instance>> {

    @Override
    public Map<String, Instance> setVertexValue() {
        return null;
    }
}

In your code, the <T> in

public abstract <T> T setVertexValue();

is a completely separate generic parameter that shadows the T in Vertex<T>.