Analysis on the Application of C # Constructor

C # What is the use of constructor? C # What is the specific effect of using constructor? This article will introduce you to this aspect.

C # The Name Of The constructor must be recognized by the compiler before it can be automatically executed. Its naming method is simple and reasonable: Let the C # constructor and class have the same name. Except for the name, the C # constructor has no return value type, which is different from the void function. If it has a return value type, the compiler will be overwhelmed. Before you can access a class's methods, attributes, or anything else, the first statement to be executed contains the C # constructor of the corresponding class. Even if you do not write a C # constructor, a default C # constructor is provided to you.

• ClassTestClass
  
• {
  
• 　PublicTestClass ():Base() {}// Provided by CLR
   
  
• }
  

The following lists several types of C # Constructor

1) default C # Constructor

• ClassTestClass
  
• {
  
• 　PublicTestClass ():Base(){}
  
• }
  

As described above, it is provided by the system (CLR.

2) instance C # Constructor

The instance C # constructor is a method member that implements initialization of the class instance. For example:

• UsingSystem;
  
• ClassPoint
  
• {
  
• 　Public DoubleX, y;
  
• 　PublicPoint ()
  
• {
  
• This. X = 0;
  
• This. Y = 0;
  
• }
  
•  
   
• 　PublicPoint (DoubleX,DoubleY)
  
• {
  
• This. X = x;
  
• This. Y = y;
  
• }
  
• ...
  
• }
  
•  
   
• ClassTest
  
• {
  
• 　Static VoidMain ()
  
• {
  
• Point a =NewPoint ();
  
• Point B =NewPoint (3, 4); // use C # To construct a function to initialize an object
   
  
• ...
  
• }
  
• }
  

Declares a class Point, which provides two C # constructor. They are overloaded. One is the PointC # constructor without parameters and the other is the PointC # constructor with two double parameters. If the C # constructor is not provided in the class, the CLR automatically provides a default C # constructor. However, once the class provides custom C # constructor, such as Point () and Point (double x, double y), the default C # constructor will not be provided, note This.

3) Static C # Constructor

Static C # constructor is a method member that implements class initialization. It is generally used to initialize static data. Static C # constructor cannot have parameters, modifiers, and call. When a class is loaded, the static C # constructor of the class is automatically called. For example:

• UsingSystem. Data;
  
• ClassEmployee
  
• {
  
• 　Private StaticDataSet ds;
  
• 　StaticEmployee ()
  
• {
  
• Ds =NewDataSet (...);
  
• }
  
• ...
  
• }
  

Declared a class of Employee with a static C # constructor. Note that the static C # constructor can only initialize static data members, rather than non-static data members. However, non-static C # constructor can assign values to static data members or initialize non-static data members.

If the class only contains static members, you can create a private C # constructor: private TestClass (){...}, However, private means that it is impossible to access the C # constructor from outside the class. Therefore, it cannot be called and no object can be instantiated by the class definition.

The above is a simple application of several types of C # constructor. The following section focuses on the class hierarchy (that is, the inheritance structure) how to Use the C # constructor of the base class and derived class. The initialization of a derived class object is completed by the base class and the derived class. The base class members are initialized by the C # constructor of the base class, and the members of the derived class are initialized by the C # constructor of the derived class.

When creating an object of A derived class, the system will call the C # constructor of the base class and the C # constructor of the derived class. The execution order of the constructed function is: first, execute the C # constructor of the base class, and then execute the C # constructor of the derived class. If the derived class has an object Member, first execute the C # constructor of the base class, then execute the C # constructor of the member object class, and finally execute the C # constructor of the derived class.

As for the C # constructor that executes the base class, the C # constructor without a parameter of the base class is executed by default. If you want to execute the C # constructor with a parameter of the base class, it must be specified in the member initialization table of the C # constructor of the derived class. For example:

• ClassA
  
• {Private IntX;
  
• 　PublicA () {x = 0 ;}
  
• 　PublicA (IntI) {x = I ;}
  
• };
  
•  
   
• ClassB:
  
• {Private IntY;
  
• 　PublicB () {y = 0 ;}
  
• 　PublicB (IntI) {y = I ;}
  
• 　PublicB (IntI,IntJ): A (I) {y = j ;}
  
• };
  
•  
   
• B b1 =NewB ();
  
• // Execute C # constructor A () of the base class A, and then execute C # constructor B () of the derived class ()
  
• B b2 =NewB (1 );
  
• // Execute C # constructor A () of the base class A, and then execute C # constructor B (int) of the derived class)
  
• B b3 =NewB (0, 1 );
  
• // Execute the C # constructor A (int) of the base class A, and then execute
  

C # constructor B (int, int)

Here, the execution sequence of the C # constructor must be clearly analyzed. In addition, if the base class A does not provide the C # constructor public A () {x = 0 ;}, in the initialization table of all C # constructor members in the derived class, you must specify the C # constructor A (I) as follows:

• ClassA
  
• {Private IntX;
  
• 　PublicA (IntI) {x = I ;}
  
• };
  
•  
   
• ClassB:
  
• {Private IntY;
  
• 　PublicB (): A (I) {y = 0 ;}
  
• 　PublicB (IntI): A (I) {y = I ;}
  
• 　PublicB (IntI,IntJ): A (I) {y = j ;}
  
• };
  

The Application of C # constructor is introduced here. I hope it will help you learn how to use C # constructor.