Question: why do I see @interface twice( inside .h and .m files in this UIViewController files I've created. the one in the .m seems to be like a constructor. is it?

.h file

```
@interface BlackTimer : UIViewController 

@end

```

.m file

```
@interface ViewController ()

@end

```

Answer: 
The @interface in the .m file is called a class extension. [Here](http://www.friday.com/bbum/2009/09/11/class-extensions-explained/) is a good link explaining it. Hope this helps.
And [here](https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjectiveC/Chapters/ocCategories.html#//apple_ref/doc/uid/TP30001163-CH20-SW1) is the Apple documentation on class extensions.
The `@interface ViewController ()` definition in the implementation file (.m) is an anonymous Category. It allows to define ivars, properties and messages your class implements without exposing them to other objects importing your public interface (.h).