掌握抽象类、接口的基本设计和应用方法。掌握上转型对象和接口回调的应用方法。 题一:抽象类与上转型对象 题二:接口与接口回调-Grasp abstract class, interface design and application of the basic methods. Grasp objects and the transformation of the application interface callback. Title I: abstract class with th