一、定義介面

   public interface ICalculate
    {
        int Add(int a, int b);
    }

二、定義實現介面類

  public class A : ICalculate
    {
        public int Add(int a, int b)
        {
            return a + b;
        }
    }

三、介面拓展

定義靜態方法和靜態類，把介面當做引數傳入到方法體

 public static class InterfaceExtend
    {
      public static int Sub( this ICalculate calculate, int a,int b)
        {
            return a - b;
        }

        public static int Maltiply(this ICalculate calculate, int a, int b)
        {
            return a * b;
        }

        public static int Division(this ICalculate calculate, int a, int b)
        {
            return a / b;
        }
 
    }
 

四、呼叫測試

           A a = new A();
            int res = a.Maltiply(2, 3);
            Console.WriteLine(res);

            res = a.Division(10, 2);
            Console.WriteLine(res);

            res = a.Sub(100,1);
            Console.WriteLine(res);