定义一个名字为Fan的类模拟风扇，属性有speed、on、redius和color。要求为每个属性定义属性方法，并提供方法tostring（）返回类中所有属性值的字符串(Define a class named Fan class simulation fan, the attributes are speed, on, redius and color. The attribute method is defined for each attribute, and the method toS