Swift Initialization - Why are multiple init functions being called?

Here's is my class with override inits

class BottomView: UIView {

    // MARK: - initilization

   override init() {
        println("init")
        super.init()
        setup()
    }

    override init(frame: CGRect) {
        println("init frame")
        super.init(frame: frame)
        setup()
    }

    required init(coder aDecoder: NSCoder) {
        println("init decoder")
        super.init(coder: aDecoder)
        setup()
    }

    func setup() {
        println("setup")
    }
}

I then initialize in my ViewController with the following code

class ViewController: UIViewController {

    let bottomView = BottomView()

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view, typically from a nib.

        bottomView.frame = CGRectMake(0.0, self.view.frame.height/2.0, self.view.frame.width, self.view.frame.height/2.0)
        bottomView.autoresizingMask = UIViewAutoresizing.FlexibleWidth | UIViewAutoresizing.FlexibleHeight | UIViewAutoresizing.FlexibleTopMargin
        self.view.addSubview(bottomView)

    }
}

And my output is

init
init frame
setup
setup

So my question is, why is init(frame:) being called?