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 toString () returns the string of all attribute values in the class)