Generic interfaces

Question

Given the interface and class below, why do I get an "unexpected type" error when I compile IncEnter?
public interface Funcion <T>
            public T aplicar(T n);      
public class IncEnter implements Funcion<int>
            public int aplicar(int n){
                        return n + 1;
Thanks!

Answer 1

Ok...
   public interface Funcion
      public int aplicar(int n);   
public class Doble implements Funcion
     public int aplicar(int n){
          return n + n;
public class Incrementar implements Funcion
     public int aplicar(int n){
          return n + 1;
public class Map1
     public void map(Funcion fun, int[] lista){
          for(int i=0; i<lista.length; i++)
               lista[i] = fun.aplicar(lista);
public class UsaMap1
     public static void main(String [] args){  
          int[] lista = {0,1,2,3,4,5,6,7,8,9};
          Map1 m = new Map1();
          Funcion f = new Incrementar();
          m.map(f,lista);
          for (int i=0; i<lista.length; i++)
               System.out.println(lista);
          System.out.println("---");
          f = new Doble();
          m.map(f,lista);
          for (int i=0; i<lista.length; i++)
               System.out.println(lista[i]);
          System.out.println("---");          
I want a generic version of the function map (which implies that "Funcion" must be generic too) and I don't know how to do it...