C interface

Be careful ：1、 The interface cannot contain fields , Such as variable , Otherwise, the compilation will report an error ;
2、 Members in an interface cannot have definitions , For example, you cannot write a method body ;
3、 An interface is the implementation specification of a class , In other words, the interface specifies the prototype of the method, and there are classes to implement the prototype defined by the interface , Call the interface definition method prototype through class inheritance interface
4、 The class calling the interface must implement the method prototype defined in the called interface
5、 The method prototype of the class calling interface must have sufficient access rights （public）
6、 Interface can realize that the interface calls the same interface and different classes
7、 A class can implement multiple interfaces （ class ： Interface 1, Interface 2{}）
8、 Once the interface is implemented , The implementation class must implement all members in the interface , Unless the implementation class itself is an abstract class .
9、C# It's single inheritance , The interface is to solve C# The inner class can inherit multiple base classes at the same time .
10、 Interface cannot be instantiated directly
The difference between interface and abstract class ：
1、 The interface is used to specify , Abstraction is used for commonality ; Abstract classes are intelligent classes that are inherited by sheets , The interface can implement multiple inheritance .
2、 Interfaces can only declare methods 、 attribute 、 event 、 Indexer , Abstract classes can be implemented with methods , You can also define variables of non static classes
 

// Case study 
//USB Realization ： Can point 、 Can blow 

    interface IUSB
    {
        // This method has no method body , The default is 
        //public、virtual、abstract modification 
        void ChaBa();
    }
    class ShuBiao:IUSB
    {
        public  void ChaBa()
        {
            Console.WriteLine(" Can point ");
        }
    }

    class FengShan:IUSB// Class implementation interface 
    {
        public void ChaBa()
        {
            Console.WriteLine(" Can blow ");
        }
        
    }

        static void Main(string[] args)
        {
            //IUSB a = new IUSB();
            IUSB a = new FengShan();// polymorphic 
            a.ChaBa();
        //   // a = new ShuBiao();// polymorphic 
        //   // a.ChaBa();

        //    IUSB b = new ShuBiao();// polymorphic 
        //    b.ChaBa();

        //    FengShan fs = new FengShan();// object-oriented programming 
        //    fs.ChaBa();
        //}

// Interface is a capability 
// Case study 
    abstract class Door
    {
      public abstract void OpenDoor();
      public abstract void CloseDoor();
    }
    interface Lock
    {
        void OpenLock();
        void CloseLock();
    }
    class FangDaoDoor:Door,Lock
    {
        public override void OpenDoor()
        {
            Console.WriteLine(" Open door ");
        }
        public override void CloseDoor()
        {
            Console.WriteLine(" close ");
        }
        public void OpenLock()
        {
            Console.WriteLine(" The lock ");
        }
        public void CloseLock()
        {
            Console.WriteLine(" locked ");
        }
        //static void Main(string[] args)
        //{
        //    FangDaoDoor fd = new FangDaoDoor();
        //    Door d = fd;
        //    Lock a = fd;
        //    d.CloseDoor();
        //    a.CloseLock();
        //    a.OpenLock();
        //    d.OpenDoor();
        //}
    }

// An interface is a convention 
// Case study 
    interface Printer
    {
        void PrintA4();
        void PrintB5();
    }
    class User:Printer
    {
        string color;
        public void PrintA4()
        {
            color = " colour ";
            Console.WriteLine(" Print "+color+"A4 paper ");
        }
        public void PrintB5()
        {
            color = " Black and white ";
            Console.WriteLine(" Print " + color + "B5 paper ");
        }
        static void Main(string[] args)
        {
            Printer p = new User();
            p.PrintA4();
            p.PrintB5();
        }
    }