ToString method why its not called implicitly for objects

Question

class Building { }
public class Example
public static void main()
Building b = new Building();
String s = (String)b;
in the 5th Line it shows error that cannot cast building type to string..
but all classes have the toString method which is called whenever we give the object arguement in System.out.println();
the following code compiles
class Building { }
class Example
public static void main()
Building b = new Building();
System.out.println(b);
can anyone explain this?

Answer 1

I get your point about casting.
but in the println statement when u pass the building object it calls the toString method and generates a new string object
why does not it do the same in the below code.
String s = b;// b is a building object
is the tostring method implicitly called only in println where it expects a string?