Java compile time run time overloading

Main.java

public class Main {

  static class Root {}
  static class Sub extends Root {}

  public static void main(String[] args) {
    foo(new Sub());

    Root r = new Sub();
    foo(r);
  }

  static void foo(Sub s) {
    System.out.println("sub");
  }

  static void foo(Root r) {
    System.out.println("root");
  }

}

/* This prints:


sub
root

*/