Object-oriented = Object + class + inheritance + Message Communication
An object is an entity used to describe objective things in a system. It is the basic unit of a system. Object-oriented software systems are composed of objects, and complex objects are composed of Simple objects. That is to say, object-oriented technology uses Object decomposition to replace traditional functional decomposition methods. The three elements of an object include the object identifier, attribute, and service.
A class is an abstract definition of one or more objects with the same attributes and services. A class and an object are the relationships between Abstract descriptions and specific instances. A specific object is called an instance of a class.
Objects and classes are the basic concepts of object-oriented technology. Other concepts are derived from or based on them. Only development technologies with objects, classes, inheritance, and messaging features are truly object-oriented technologies.
Simply put, the so-called object-oriented means that all the work of software system development is centered around "objects", and all the work is guided by the "objects" as the center.