abstract和interface

1.abstract 的应用

    abstract class ShapesClass
         {
             public abstract int Area();
         }
         class Square : ShapesClass
         {
             int side = ;

             public Square(int n)
             {
                 side = n;
             }
             // Area method is required to avoid
             // a compile-time error.
             public override int Area()
             {
                 return side * side;
             }

         }

2.

 public interface I
        {
            int M();
        }
        public abstract class C : I
        {
            public abstract int M();
        }
        public class Des : C
        {
            public override int M()
            {
                return 100;
            }
        }

　　

    Square sq = new Square();
    sq.Area();
    int asa = new Des().M();