C # syntax exercise (11): class [3]-constructor, destructor, base, and this

Constructor and destructor:

Using system; Class myclass {private int fnum; Public int num {get {return fnum ;}}/* the constructor has no return value, the default */Public myclass () {This. fnum = 2009;}/* can have multiple constructors with different parameters */Public myclass (int x) {This. fnum = x;} public myclass (Params int [] ARR) {foreach (int I in ARR) This. fnum + = I;}/* The Destructor has no parameters, no return values, no access modifier, and can only have one */~ Myclass () {// destructor is automatically called} class program {static void main () {myclass obj1, obj2, obj3; obj1 = new myclass (); console. writeline (obj1.num); // 2009 obj2 = new myclass (100); console. writeline (obj2.num); // 100 obj3 = new myclass (1, 2, 3); console. writeline (obj3.num); // 6 console. readkey ();}}
 

If there is no constructor or destructor, the default (or inheritance) will be used for new. A private constructor can prevent the class from being instantiated:

using System;class MyClass{    private MyClass() { }    public static void Msg1() { Console.WriteLine("Msg1"); }    public static void Msg2() { Console.WriteLine("Msg2"); }}class Program{    static void Main()    {        MyClass.Msg1(); //Msg1        MyClass.Msg2(); //Msg2        Console.ReadKey();    }}
 

If a class has a non-default constructor, you cannot use the default constructor:

using System;class MyClass{    private int FNum;    public int Num { get { return FNum; } }    public MyClass(int x, int y)    {        this.FNum = x + y;    }}class Program{    static void Main()    {        MyClass obj;        obj = new MyClass(1, 2);        Console.WriteLine(obj.Num); //3        Console.ReadKey();    }}
 

Static constructor:

The static constructor has no access modifier or parameter;
The static constructor is automatically called before new or any static member is called;
Static constructors are generally used to initialize static data;
A static constructor is triggered before the first new or first use of a static member;
Static constructor cannot be called directly.

using System;class MyClass{    public static int Num;    public static void ShowNum() { Console.WriteLine(Num); }    public void Msg() { Console.WriteLine("Msg"); }    static MyClass() { Num = 123; }}class Program{    static void Main()    {        MyClass.ShowNum();            //123        MyClass.Num = 2009;        MyClass.ShowNum();            //2009        MyClass obj1 = new MyClass();        obj1.Msg();                   //Msg        Console.ReadKey();    }}
 

Automatically call the constructor of the parent class:

using System;class Parent{    public Parent() { Console.WriteLine("Parent"); }}class Child1 : Parent{    public Child1() { Console.WriteLine("Child1"); }    public Child1(int x) { Console.WriteLine(x); }}class Child2 : Child1{    public Child2() { Console.WriteLine("Child2"); }    public Child2(int x, int y) { Console.WriteLine(x + y); }}class Program{    static void Main()    {        Parent p = new Parent();           // Parent        Child1 c1 = new Child1();          // Parent / Child1        Child2 c2 = new Child2();          // Parent / Child1 / Child2        Child1 c11 = new Child1(999);      // Parent / 999        Child2 c22 = new Child2(111, 222); // Parent / Child1 / 333                Console.ReadKey();    }}
 

Base:

using System;class Parent{    public Parent() { Console.WriteLine("Parent"); }    public Parent(int x, int y) { Console.WriteLine(x + y); }    public Parent(string s1, string s2) { Console.WriteLine(s1 + s2); }}class Child1 : Parent{    public Child1() { Console.WriteLine("Child1"); }}class Child2 : Parent{    public Child2() : base() { Console.WriteLine("Child2"); }}class Child3 : Parent{    public Child3() : base(111,222) { Console.WriteLine("Child3"); }}class Child4 : Parent{    public Child4() : base("111", "222") { Console.WriteLine("Child4"); }}class Program{    static void Main()    {        Child1 c1 = new Child1(); // Parent / Child1        Child2 c2 = new Child2(); // Parent / Child2        Child3 c3 = new Child3(); // 333 / Child3        Child4 c4 = new Child4(); // 111222 / Child4                Console.ReadKey();    }}
 

This:

using System;class MyClass{    private string fs = "ABC-";    public MyClass() { Console.WriteLine("MyClass"); }    public MyClass(string str) { Console.WriteLine(this.fs + str); }    public MyClass(int num) : this() { Console.WriteLine(num); }    public MyClass(int x, int y) : this("XYZ") { Console.WriteLine(x + y); }}class Program{    static void Main()    {        MyClass c1 = new MyClass();          // MyClass        MyClass c2 = new MyClass("EFG");     // ABC-EFG        MyClass c3 = new MyClass(123);       // MyClass / 123        MyClass c4 = new MyClass(111, 222);  // ABC-XYZ / 333        Console.ReadKey();    }}
 

Constructors, attributes, and base:

using System;abstract class Parent{    private byte FID;    public Parent(byte n)    {        FID = n;    }    public byte Id    {        get { return FID; }        set { FID = value; }    }}class Child : Parent{    public Child(byte MyID) : base(MyID) { }}class Program{    static void Main()    {        Child Rect = new Child(6);        Console.WriteLine(Rect.Id); //6        Rect.Id = 8;        Console.WriteLine(Rect.Id); //8        Console.ReadKey();    }}