https://fckup.ru/question/%d1%87%d1%82%d0%be-%d1%82%d0%b0%d0%ba%d0%be%d0%b5-%d0%b0%d0%b1%d1%81%d1%82%d1%80%d0%b0%d0%ba%d1%82%d0%bd%d1%8b%d0%b9-%d0%bc%d0%b5%d1%82%d0%be%d0%b4-abstract-method-%d0%b2-%d0%be%d0%b1%d1%8a%d0%b5/