Observer design pattern of design pattern

Recently, I'd like to supplement the knowledge related to design patterns. About observer design patterns, I mainly learn from the following aspects, as follows:

Here is a mind map of this section, as follows:

What is the observer design pattern

Understanding of key concepts

How to notify the observer

Implementation of observer mode

1. Handwriting observer mode

2. Observer design pattern provided by Java API

Advantages and disadvantages of observer mode

Usage scenario