Bounded Wildcard arguments.

   
   
class TwoD {
  int x, y;

  TwoD(int a, int b) {
    x = a;
    y = b;
  }
}

class ThreeD extends TwoD {
  int z;

  ThreeD(int a, int b, int c) {
    super(a, b);
    z = c;
  }
}

class FourD extends ThreeD {
  int t;

  FourD(int a, int b, int c, int d) {
    super(a, b, c);
    t = d;
  }
}

class Coords<T extends TwoD> {
  T[] coords;

  Coords(T[] o) {
    coords = o;
  }
}

class BoundedWildcard {
  static void showXY(Coords<?> c) {
    System.out.println("X Y Coordinates:");
    for (int i = 0; i < c.coords.length; i++)
      System.out.println(c.coords[i].x + " " + c.coords[i].y);
    System.out.println();
  }

  static void showXYZ(Coords<? extends ThreeD> c) {
    System.out.println("X Y Z Coordinates:");
    for (int i = 0; i < c.coords.length; i++)
      System.out.println(c.coords[i].x + " " + c.coords[i].y + " " + c.coords[i].z);
    System.out.println();
  }

  static void showAll(Coords<? extends FourD> c) {
    System.out.println("X Y Z T Coordinates:");
    for (int i = 0; i < c.coords.length; i++)
      System.out.println(c.coords[i].x + " " + c.coords[i].y + " " + c.coords[i].z + " "
          + c.coords[i].t);
    System.out.println();
  }

  public static void main(String args[]) {
    TwoD td[] = { new TwoD(0, 0), new TwoD(7, 9), new TwoD(18, 4), new TwoD(-1, -23) };

    Coords<TwoD> tdlocs = new Coords<TwoD>(td);

    System.out.println("Contents of tdlocs.");
    showXY(tdlocs); // OK, is a TwoD

    FourD fd[] = { new FourD(1, 2, 3, 4), new FourD(6, 8, 14, 8), new FourD(22, 9, 4, 9),
        new FourD(3, -2, -23, 17) };

    Coords<FourD> fdlocs = new Coords<FourD>(fd);

    System.out.println("Contents of fdlocs.");
    // These are all OK.
    showXY(fdlocs);
    showXYZ(fdlocs);
    showAll(fdlocs);
  }
}

Related examples in the same category

1.	Java generic: Use a wildcard.
2.	Java generic: Bounded Wildcard arguments
3.	Use a wildcard.
4.	Generic cast
5.	Generic structure with constraints
6.	Return an implementation of a Comparable

Bounded Wildcard arguments. : Constraints « Generics « Java

Related examples in the same category