class SpaceShip {}
class GiantSpaceShip extends SpaceShip {}

class Asteroid {

  public void collideWith(SpaceShip sp) {
    System.out.println("Asteroid hit a SpaceShip");
  }
  public void collideWith(GiantSpaceShip gsp) {
    System.out.println("Asteroid hit a GiantSpaceShip");
  }
}

class ExplodingAsteroid extends Asteroid {

  public void collideWith(SpaceShip sp) {
    System.out.println("ExplodingAsteroid hit a SpaceShip");
  }
  public void collideWith(GiantSpaceShip gsp) {
    System.out.println("ExplodingAsteroid hit a GiantSpaceShip");
  }
}

public class DoubleDispatchTest { public static void main(String args[]) {
    Asteroid ast = new Asteroid();
    Asteroid ast1 = new ExplodingAsteroid();
    SpaceShip sp = new SpaceShip();
    SpaceShip sp1  = new GiantSpaceShip();
 ast.collideWith(sp);
 ast.collideWith(sp1);
 ast1.collideWith(sp);
 ast1.collideWith(sp1);
 }
}

Output:
Asteroid hit a SpaceShip
Asteroid hit a SpaceShip
ExplodingAsteroid hit a SpaceShip
ExplodingAsteroid hit a SpaceShip