class Pt extends Object {
  float x;
  float y;
  boolean isXPos(Pt p) { return p.x > 0; }
  Pt(float _x, float _y) { x = _x; y = _y; }
}
class Pt3D extends Pt {
  float z;
  Pt3D(float _x, float _y, float _z) { super(_x,_y); z = _z; }
}
class C extends Object {
  void f(Pt3D p1, Pt   p2) {}
  void f(Pt   p1, Pt3D p2) {}
  void g(Pt3D p1, Pt3D p2) {
    //    f(p1,p2); // no best match!
    f(p1,(Pt)p2); // fine with static overloading
  } 
}

// 3 casts just to use composition using interface I
interface I {
  Object apply(Object o);
}
class Compose implements I {
  I f;
  I g;
  public Object apply(Object o) {
    return g.apply(f.apply(o));
  }
  Compose(I _f, I _g) {f = _f; g = _g;}
}
class A1 implements I { 
  public Object apply(Object o) { return apply((Pt) o); }
  public Pt3D apply(Pt   p) { return new Pt3D(p.x, p.y, 0);}
}
class A2 implements I {
  public Object apply(Object o) { return apply((Pt3D) o); }
  public Pt     apply(Pt3D p)   { return new Pt(p.x, p.y); }
}
class A3 {
  void f() {
    I copyPoint = new Compose(new A1(), new A2());
    Pt p = (Pt) copyPoint.apply(new Pt(3,4));
  }
}