package Ġcom . design . pattern . observer Ċ Ċ interface ĠSubject Ġ{ ĊĠĠĠ Ġfun Ġregister Observer ( observer : ĠObserver ) ĊĠĠĠ Ġfun Ġremove Observer ( observer : ĠObserver ) ĊĠĠĠ Ġfun Ġnotify Observer () Ċ }