某在线股票软件需要提供如下功能：当股票购买者所购买的某支股票价格变化幅度达到5 时，系统将自动发送通知(包括新价格)给购买该股票的股民。现使用观察者模式设计该系统-An online stock software needs to provide the following functions: when the amplitude of a stock stock buyers purchase price changes is 5 , the system will automatically send notification (including the new price) to buy the stock investors. We use the observer pattern design of the system