Classes and objects

One . Classes and objects

1、 Definition

object ： It is the abstraction of a group of objects with the same attributes and behaviors in the objective world ;
            An object is an entity used to describe an objective thing . Everything is object

          people 、 classroom 、 The notebook 、 air

class ： Classes are abstract types of objects , Object is a concrete instance of a class

        class = attribute （ Member variables ） + operation （ Functions that operate on member variables ）

        A collection of objects with the same properties and methods

        human beings 、 Fruits 、 Notebook class

2、 Format ：

[ Modifier ] class Class name {    }

Class name definition rules ：

1、 The first word must be a letter 、 Underline , The following words can be letters 、 Underline 、 Numbers

2、 All words must be capitalized

Class field ： Access modifier + data type + Field name

Class content

[ Modifier ] class Class name

{   

attribute ;

Method ;

}

 // attribute

    char sex = ' male ';

    float shenGao = 1.75f;

    string a = " Light yellow ";// Hair color

    // Method

    void Smile()

    {

        Debug.Log(sex);

        print(shenGao);

        Debug.Log(a);

    }

3、 Object creation ：

Class name Object name ( Variable )=new Class name ();

LiJiangTao ljt = newLiJiangTao();

4、 Calls to properties and methods

attribute ： An extension to the field

Call properties and methods with spot Operator

LiJiangTao ljt = newLiJiangTao();

        print(ljt.sex);// Call the property

        ljt.Smile();// Calling method

5、 Method definition ：

                               public         void          print     {int a,int b} {...}
                              Access modifier   return type   Method name     parameter list
                              It is generally public

                              Outside the class, you can access the private members of the class through the public member methods

Return type ： data type （ basic 、 quote ）、void（ No return value ）

6、 Method operation ：

Method definition ：

If the method does not return a value , Then this method must output the result

If the method has a return value , Then this method can not output the result , But there must be a return value

The return value uses the keyword :return

Method call ：

Call a method with no return value ： Object name . Method name ();

Call a method with a return value ： Variable = Object name . Method name ();

// Let's define a triangle class , Define two methods , Find the perimeter and area of a triangle

    int a = 3, b = 4, c = 5;// Three sides

    // Perimeter method has no return value

    void ZhouChang() {

        int d=a+b+c;

        print(" The circumference of a triangle is ："+d);

    }

    // The area method has a return value

    int MianJi() {

        int e = a * b / 2;

        return e;

    }

1. Methods with parameters

classZhaZhiJi

    {

        // Juicing method

        // Give Party A something to drink

        string JiaFangZhaZhi(string shuiGuo) {

            string s = " Have a drink "+shuiGuo+" juice ";

            return s;

        }

         static void Main(string[] args)

         {

           ZhaZhiJi zzj = new ZhaZhiJi();

           zzj.ZhaZhi(" Apple ");// The actual parameter ： Actual parameters

           string st = zzj.JiaFangZhaZhi(" durian ");

           Console.WriteLine(st);

           Console.ReadKey();

        }

        // Drink it yourself

        void ZhaZhi(string shuiGuo)// Formal parameters ： Shape parameter

        {

            Console.WriteLine(" Have a drink "+shuiGuo+" juice ");

        }

    }

1. Local variables and member variables

string name ;// Member variables , The system provides a value by default

void Print(){

      int age=20;// local variable

      Console.WriteLine(age);

      Console.WriteLine(name);

}

Different scopes

The scope of a local variable is limited to the methods that define it

The scope of the member variable is visible throughout the class

Different initial values

The system will give the member variable an initial value

The system does not assign initial values to local variables

1.static

The difference between static variables and instance variables ：

1、 Static variables have only one memory space in memory , In the process of loading classes, complete the memory allocation of static variables ; Every time a new instance object is created , Different memory will be allocated for instance variables

2、 Static variables can be accessed directly through the class name , Instance variables need to be accessed through various objects

//static： static state

        int x = 1;

        staticint y = 1;// Static variables 、 Class variables

        void Get()

        {

            x++;

            y++;

            Console.WriteLine(x + "\t" + y);

        }

        staticvoid Main(string[] args)

        {

            Test12 t1 = newTest12();

            Console.WriteLine(t1.x + "\t" + Test12.y);

            t1.Get();

            Test12 t2 = newTest12();

            t2.Get();

}

The difference between static method and instance method ：

1. Static methods can only access static variables ; Instance methods can access instance variables , You can also access static variables
2. Static methods in Main Method can be used directly ; The instance method is in Main Method must be called through an object

classTest13

    {        

        int value=10;// Member variables 、 Instance variables

        staticint a = 2;// Static variables 、 Class variables

        void Print3()// Member method 、 Example method

        {

            Console.WriteLine(value);

            Console.WriteLine(a);

        }

       staticvoid Print()// Static methods 、 Class method

        {

            //Console.WriteLine(value);

            Console.WriteLine(a);

        }

       //static void Main(string[] args)

       //{

       //    Test13 t1 = new Test13();

       //    Print();

       //    t1.Print3();

       //    //int a = 10;

       //    //Print(a);

       //    //Console.WriteLine(a);

         

       //    //Print2(t1);

       //    //Console.WriteLine(t1.value);

       //    //t1.Get();

       //    //t1.Get();

       //    //t1.Get();

       //    //t1.value = 10;

       //    //Test13 t2 = t1;// References to objects

       //    //t2.value++;

       //    //Console.WriteLine(t1.value + "\t" + t2.value);

       //}

1. this

//this： Refers to instances of classes

this Usage of ：

1、 When a member variable and a local variable have the same name , If you want to call member variables , use this

2、 When constructors call each other , use this

        string name;

        int age;

        double salary;

        public Worker():this(" Du Cheng ", 19, 6000)

        {

            //name = " Yuan Huabin ";

            //age = 18;

            //salary = 5000;

            //Console.WriteLine(name + "\t" + age + "\t" + salary);

        }

        //public Worker(string name, int age, double salary):this()

        public Worker(string name, int age, double salary)

        {

            this.name=name;

            this.age = age;

            this.salary = salary;

            Console.WriteLine(name + "\t" + age + "\t" + salary);

        }

1. Construction method

Definition ：

Methods with the same method name and class name , There is no return type , And there's no void.

features ： If there is no writing constructor   The system will provide a parameterless construction method by default , The method is empty

       If write Will override the system default

effect ： Initialize member variables

1. Method overloading

Same class Multiple methods in can have identical Method name of , But there are Different parameter lists , This is called method overloading

Method overload rules ：

• The method name must be the same .
• Parameter list must be different .
• Methods can have the same or different return types .
• Just because the return type is different is not enough to be called method overloading .

1. References to objects

classTest14  {

        int a = 1;

        void Get()

        {

            Console.WriteLine(a);

        }

        void Get2(Test14 t)// The third kind of quotation

        {

            t.a++;

        }

        Test14 Get3(Test14 t)// The fourth kind of quotation

        {

            t.a++;

            return t;

        }

        staticvoid Main(string[] args)

        {

            Test14 t = newTest14();

            t.a = 2;// First reference

            Test14 t2 = t;// The second quotation

            //Console.WriteLine(t.a+"\t"+t2.a);// 2  2

            //t2.Get();

            //t.Get2(t);

            //Console.WriteLine(t.a + "\t" + t2.a);// 3  3

            Test14 t3 = t.Get3(t);

            t3.a++;

            Console.WriteLine(t.a + "\t" + t3.a);// 4  4

        }