(1) All things are objects,
Take those things that can be seen, as well as an invisible thing, or you can think of, each object has its own properties and behavior
(2) Each program is a collection of a lot of objects
(3) Each object has its own storage space to accommodate other objects
(4) Each object has a type
(5) All objects can receive the same message
Object-oriented methods are to simplify all things, unify, do not have to be limited to specific types
