Class & Objects

对象，不存在的

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data type(数据类型)

Procedural and Object-Oriented Programmming

• Procedural programming focuses on the process/actions that occur in a program

• Object-Oriented programming is based on the data and the functions that operate on it. Objects are instances of new data types that represent the data and the operations on that data.

Procedural Programming

• So far the focus is on the steps, actions, and functions.

  • Data is subordinate to functions

• Object Oriented Programming

  • Focus is on the data

  • Functions are subordinate to the data

Limitations of Procedural Programming

• ​If the data structures change, many functions must also be changed

• Programs that are based on complex function hierarchies are:

  • difficult to understand and maintain

  • difficult to modify and extend

  • easy to break

Object-Oriented Programming Terminology

• Class: like a struct (allows bundling of related variables), but variables and functions in the class can have different properties than in a struct

• Object: an instance of a class, in the same way that a variable can be an instance of a struct

Object-Oriented

• Model real world objects(mostly)

• Bunding

  • Related data (Attributes)

    • in C++ called data members

  • Related methods (Actions)

    • in C++ callled member functions

• Communication occurs through messages

  • Object is spoken to by calling a method on it

Concept of class

• Class is a generic description

  • Think blueprint

• Object is an instance of the class

  • Think the blue house on the corner

  • And the red one on the next block

  • And the green one next door

  • I.e. there are multiple instances of a single class

Visibility

visibility

• data hiding: restricting access to certain members of an object

• public interface: members of an object that are available outside of the object. This allows the object to provide access to some data and functions without sharing its internal details and design, and provides some protection from data corruption

interface

C++ Note

• struct and class are almost interchangeable in C++

  • struct was used in C for heterogeneous data

  • class adopted into C++ (label was common in other languages)

    • class concept groups not only heterogeneous data, but the methods that act on them.

    • This capability was given to structs as well.

• Differ in default visibility

  • class is private by default

  • struct is public by default