. NET Fundamentals Review (III)

A. Richter Replacement principle: LSP

Definition: Subclasses can replace the location of the parent class, and the function of the program is not affected (the parent class variable points to the subclass object). Because there are functional subclasses of the parent class, they do not affect the functionality of the program.

Examples of programs:

 1  person p = new   person ();  2  p.sayhi (); //  call the parent class  3  Student s = new   Student ();  4  s.sayhi (); //  call the subclass  5   Richter Replacement principle  6  person p1 = new   Student ();  7  P1. Sayhi (); //  Call the parent class's  

two. Type Conversions

1. bool B = p is person; determines the type of class that the variable refers to.

2. As conversion

Person p = new person ();

Student S1 = (Student) p;//may report an exception

If the conversion succeeds, the reference points to S2, and if the conversion fails, returns null

Student s2 = p as Student;

Three Virtual method, polymorphic

1. Virtual method: Allows subclasses to override methods of the parent class.

Examples of programs:

1 //Person.cs2 class Person3     {4          Public Virtual voidSayhi ()5         {6Console.WriteLine ("I'm a human being. ");7         }8 }9 Ten //Chinese.cs One classChinese:person A     { -          Public Override voidSayhi () -         { theConsole.WriteLine ("I am a Chinese. "); -         } - } -  + //GuangDongRen.cs - classGuangdongren:chinese +     { A          Public Override voidSayhi () at         { -Console.WriteLine ("I am a Cantonese person. "); -         } -     } -  - //Main in Static voidMain (string[] args) -         { toPerson p =NewGuangdongren (); + P.sayhi (); - //export of "Guangdong people" the             //if the Guangdongren class does not override the Sayhi () method, the output "Chinese" *  $ Console.readkey ();Panax Notoginseng}

2. Polymorphism, the same behavior, for different things, there are different manifestations.

Examples of programs:

1 //Person.cs2  Public Virtual voidwashbody ()3         {4Console.WriteLine ("people in the shower");5         }6 7 //Boy.cs8 classBoy:person9     {Ten          Public Override voidwashbody () One         { AConsole.WriteLine ("Boy in the shower"); -         } -     } the  - //Girl.cs - classGirl:person -     { +          Public Override voidwashbody () -         { +Console.WriteLine ("Girl in the shower"); A         } at } -  - //WashMachine.cs - classWashmachine -     { -          Public voidWash (person p) in         { -Console.WriteLine ("Start Bathing"); to p.washbody (); +Console.WriteLine ("Bath End"); -         } the     } *  $ //MainPanax Notoginseng Static voidMain (string[] args) -         { theBoy P1 =NewBoy (); +Girl P2 =NewGirl (); AWashmachine WM =Newwashmachine (); theWm. Wash (p1);//Boy Bathing +Wm. Wash (p2);//Girl Bathing -Console.readkey ();

3. Use the parent class type as the return value of the method. (What is the principle?) ）

Examples of programs:

1 //Pet.cs2 classPet3 {4      Public Virtual voidShout ()5     {6Console.WriteLine ("Pets are called");7     }8 }9 Ten //Cat.cs One classCat:pet A { -      Public Override voidShout () -     { theConsole.WriteLine ("The cat called"); -     } - } -  + //Dog.cs - classDog:pet + { A      Public Override voidShout () at     { -Console.WriteLine ("Dog Barking"); -     } - } -  - //Shop.cs in class Shop - { to      PublicPet Sellpet (stringtype) +     { -         Switch(type) the         { *              Case "Dog": $                 return NewDog ();Panax Notoginseng              Case "Cat" -                 return NewCat (); the             default: +                 return NULL; A         } the     } + } -  $ //Main $ Static voidMain (string[] args) - { -Shop shop =NewShop (); thePet pet = shop. Sellpet ("Dog"); -Pet. Shout ();//output "Dog bark"Wuyi}

. NET Fundamentals Review (III)