C# class and object access modifiers and constructor C# learning miscellaneous (eight)

Class (class) is the basic C# type. A class is a data structure that combines fields and methods in one unit.

1. Defined class
Defined class generally includes: modifier, class , class name.
Without modifier, it defaults to private class

    //定义 学生类
    class Student
    {
    
    
        //数据-变量
        public string name;
        public int age;

        //行为-方法
        public void SayName()
        {
    
    
            Console.WriteLine("我是:" + name);
        }
    }
      //矩形类
    class Rect
    {
    
    
        //数据
        public float l;//长
        public float w;//宽
    
        //行为
        public float GetArea()  //求面积
        {
    
    
            return l * w;
        }

        public float GetPerimeter() //求周长
        {
    
    
            return (l + w) * 2;
        }
    }

Class generally contains class members, class methods, etc.

2. Create an object

			Student s1 = new Student();//创建一个学生对象
			Rect rect1 = new Rect();//创建一个矩形对象

3. Access modifier

Access modifier	restriction of visit
public	Public, no access restrictions
private	Private, can only be accessed within this class, subclasses and instances cannot be accessed
protected	Protected, limited to this class and subclasses, the instance cannot be accessed
internal	Inside the program, only accessible within this project
protected internal	The internal protection of the program is limited to this project or sub-category access

4. Constructor
Constructor: Without writing the return value, the method name is the same as the class name.
When creating an object, the constructor will be called automatically. If there is a parent class, the parent class constructor will be called first. The constructor is mainly used to initialize member variables.
If we do not write a constructor, the system will provide a default constructor. If the constructor is written, it will no longer be provided.

   class MyClass
    {
    
    
        public int x;
        public int y;
        public int z;
        
        public MyClass()
        {
    
    
        }

        public MyClass(int x,int y) //我们写的有参数的构造函数
        {
    
    
            this.x = x;
            this.y = y;
        }

        public MyClass(int x, int y, int z) :this(x,y)
        {
    
    
            this.z = z;
        }
    }

Among them : this() is to call the sibling constructor, that is, to call the above

 		public MyClass(int x,int y) 
        {
    
    
            this.x = x;
            this.y = y;
        }

Avoid duplication of code.