delegate

class Main {
    public static void main(String[] args) {
        Main m = new Main()
    }

    Main() {
        String[] a = ["Hello world!"]
        Box b = new TextBox(a)
        b.click = {
            content.add("You clicked this box!")
        }
        b.onClick()

        println b.content
    }

    class Box {
        Closure click

        Box () {
            click = {}
        }

        void onClick() {
            click.delegate = this
            click()
        }
    }

    class TextBox extends Box {
        List<String> content

        TextBox (String[] a) {
            super()
            content = a
        }
    }
}