package Ġorg . df re er . design patterns . observer . weather Ċ Ċ interface ĠSubject Ġ{ ĊĠĠĠ Ġfun Ġadd Observer ( observer : ĠObserver ) ĊĠĠĠ Ġfun Ġdelete Observer ( observer : ĠObserver ) ĊĠĠĠ Ġfun Ġnotify Observer s () Ċ } Ċ