abstract和interface

1.abstract 的应用

 1    abstract class ShapesClass
 2         {
 3             public abstract int Area();
 4         }
 5         class Square : ShapesClass
 6         {
 7             int side = 0;
 8 
 9             public Square(int n)
10             {
11                 side = n;
12             }
13             // Area method is required to avoid
14             // a compile-time error.
15             public override int Area()
16             {
17                 return side * side;
18             }
19 
20 
21         }

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