Introduction - If you have any usage issues, please Google them yourself
Object-oriented concepts: Classes and Objects, classes are the basic elements of the Java object-oriented programming, which defines the structure and function of an object' s constructor, class inheritance, " This" and " the super 4-class variable (static type) methods and instance variables, methods, methods cover and overloading, abstract classes and interfaces 6, object-oriented features, object-oriented design principles