Generic Implementation of Directed Graph

Question

I am having issues in implementing the Generic DirectGraph Implementation. Please help me!

public interface DirectedGraph<Vertex<T extends Comparable<T>>> {
   <T extends Comparable<T>> boolean  addVertex(Vertex<T> v);
   <T extends Comparable<T>> boolean addEdge(Vertex<T> v1, Vertex<T> v2);
   int size();
   <T extends Comparable<T>>boolean removeEdge(Vertex<T> v1, Vertex<T> v2);
   <T extends Comparable<T>>boolean hasEdge(Vertex<T> v1, Vertex<T> v2);

}

public class Vertex<E extends Comparable<E>> {
  E vertex;
}

What is wrong with the above code?. Eclipse is showing the error

Multiple markers at this line
- Syntax error on token "<", , expected
- The type parameter Vertex is hiding the type 
 Vertex<E>
- Syntax error on token ">>>", >> expected

Answer 1

Either you make a class generic or a method generic.In your case,you are doing both.Also,since you have decided that DirectedGraph will use Vertex type,it is not the class Vertex but type "Vertex" .You use a concrete class or interface type when you use the class or generic method and not in the definiton itself

public interface DirectedGraph<T extends Comparable<T>> {
        boolean  addVertex(Vertex<T> v);
        boolean addEdge(Vertex<T> v1, Vertex<T> v2);
        int size();
        boolean removeEdge(Vertex<T> v1, Vertex<T> v2);
        boolean hasEdge(Vertex<T> v1, Vertex<T> v2);

    }

    class Vertex<E extends Comparable<E>> {
      E vertex;
    }