Design Pattern learning 2-Observer pattern (observer)

This mode was very interesting for a while. After three hours, I finally understood it. Haha, it's not very complicated ......

Observer Mode

Official explanation:......

Personal Understanding: observer ...... A group of people are chatting. When a person says this, others are "observing" and get the "information" said by the speaker. The "observing" person can also speak, as a result, others become "observers", and those who are talking are called "theme ".

Small Example: the Technical Support Center should select "38 red Flagstaff". candidates include A, B, and C. Everyone can vote and everyone wants to know the result. Therefore, the central vote is "subject (object)", while all other Members are "Observer (observer) ". Draw a picture.
Source code download (because the code written after drawing is not the same, but the structure is still very clear .)