Java method override - parent method is called when a parameter is used

Here is the code I wrote:

https://pastebin.com/raw/0iBrGJR4

Most relevant parts:

    A a = new A();
    B b = new B();    

    System.out.println(((A) b).a());    
    System.out.println(((A) b).b(3));    


  static class A {
    Object a() {
      System.out.println("A.a()");
    }

    Object b(Number x) {
      System.out.println("A.b()");    
    }
  }


  static class B extends A {
    String a() {
      System.out.println("B.a()");
      return "hello";
    }

    String b(Integer x) {
      System.out.println("B.b()");
      return "hola" + x;
    }
  }

When I run this, the first print displays

B.a()
hello

which is what I expected, since even though we cast to A, the call goes through to the object's actual type which is B.

But the second print, the ((A) b).b(3) call, prints

A.b()
3

(i.e. it calls the method in A). Force casting 3 to Integer doesn't do anything either. Can someone explain this behavior to me? I don't understand what the reason is. I would've expected ((A) b).b(3) to print B.() \n hola3 rather than use the parent class method.