C# One Week Introductory "C# - Classes and Objects" Day Six

导言：Go through the knowledge of classes and objects again here,

一、类和对象

1. 类是什么？

A class is a syntactic representation used to describe objects in the real world,It is an abstraction of the human mind.

2. 对象是什么？

The object here mainly refers to the use of computer language to describe things in reality.is the object that will be instantiated.

3. 类与对象的关系

A real object necessarily falls under our human classification,有很多属性,Take people, for example,A person has many attributes,有年龄、姓名、性别等等,在c#You can use classes in it、结构体、etc. syntax to describe the information that represents a person,But people don't just have attributes,还有行为,Like being able to sing,able to dance etc.Structs are obviously inconvenient to describe behavior,Structures mainly store data,It just so happens that the class has the function of describing the behavior of the object with functions,So classes are the best practice for describing objects.

二、C#类语法

1. 类的语法

类语法 使用 class 关键字 和 statement block to describe,Declare a class instance as follows

public clsss  Person
{
    
	string Name;
	int Age;
	bool Sex;

	public void Dance()
	{
    
		//跳舞
		Console.WriteLine("I Can Dance!");
	}

	public void Sing()
	{
    
		//唱歌
		Console.WriteLine("I Can Sing!");
	}
}

How to use a class to generate an object？
使用 new 关键字即可

Person zhangShan = new Person();
zhangShan.Dance();
//zhangShanThis subject has just performed a dance

• 没有默认构造函数 会自动生成构造函数
• To access objects using is “.” symbolic access

2. 类的访问权限

类的默认访问标识符是 internal,成员的默认访问标识符是 private.These symbols govern classes、Class member accessors
The general class of access I generally write is public
Let's briefly discuss it 类成员的访问 标识符

• public：The instantiated object can be accessed
• private：The instantiated object cannot be accessed

public clsss  Person
{
    
	public string Name = "张珊";
	public int Age;
	private bool Sex;	

	public Person()
	{
    
	}

	public void Dance()
	{
    
		//跳
		Console.WriteLine("I Can Dance!");
	}

	public void Sing()
	{
    
		//唱
		Console.WriteLine("I Can Sing!");
	}
	private void Rap()
	{
    
		//Rap
		Console.WriteLine("I Can Rap!");
	}
}

我们在使用时,Know what the following situations mean

Person zhangShan = new Person();

//正确
zhangShan.Dance();
zhangShan.Sing();
var name = zhangShan.Name;
var age = zhangShan.Age;

//错误-不能访问
zhangShan.Rap();
zhangShan.Sex();

3. 特殊函数

1、构造函数

类的 构造函数 是类的一个特殊的成员函数,当创建类的新对象时执行.也就是只执行一次
构造函数的名称与类的名称完全相同,它没有任何返回类型.

public clsss  Person
{
    
	//............

	public Person(/*可跟参数*/)
	{
    
		//...........
		//初始化某些值,
	}
}

2、析构函数

类的 析构函数 是类的一个特殊的成员函数,当类的对象超出范围时执行.That is to say, we do not automatically call、Also do not call manually
析构函数的名称是在类的名称前加上一个波浪形（~）作为前缀,它不返回值,也不带任何参数.
析构函数用于在结束程序（比如关闭文件、释放内存等）之前释放资源,

```csharp
public clsss  Person
{
    
	//............

	public Person(/*可跟参数*/) //构造函数
	{
    
		//...........
		//初始化某些值,
	}
	
	~Person(/*Parameters cannot be followed*/)	//析构函数
	{
    
		//...........
		//初始化某些值,
	}
}