I always think it’s weird, why when we talk about object-oriented, there are always two ways of saying
One is the three major characteristics, the other is the four major characteristics, the reasons are as follows
The concept of abstraction is a very general design idea. It is not only used in object-oriented programming, but can also be used to guide architecture design. Moreover, this feature does not require a programming language to provide a special grammatical mechanism to support it. It only needs to provide a very basic grammatical mechanism of "function" to achieve abstract features. Therefore, it does not have a strong "specificity". It was not regarded as one of the characteristics of object-oriented programming.
What is abstraction: Abstraction is to extract the same parts and classify them. To understand from this perspective, you also know what is said above-only need to provide a very basic grammatical mechanism of "function" to achieve abstract features