0. #lang racket
1.  
2. (define top-class%
3.   (class object%
4.     (super-new)
5.  
6.     (define/public (a-method)
7.       (displayln "Hello from top class"))))
8.  
9. (define sub-class%
10.   (class top-class%
11.     (super-new)
12.  
13.     (define/private (another-method)
14.       (displayln "Hello from another method"))
15.  
16.     (define/override (a-method)
17.       (displayln "Hello from sub class")
18.       (send this another-method))))
19.  
20. (send (new sub-class%) a-method)

=>

Hello from sub class

send: no such method

method name: another-method

class name: sub-class%