.NET 泛型的特殊使用

定义泛型的后面加where子句,可以要求,该泛型定义的参数必须满足一定条件:如实现了一定接口,继承自某一基类,具有一个无参构造函数等.

 

using System;
using System.Collections.Generic;
using System.Text;
namespace GenericWhereDemo
...{
    class Program
    ...{
        static void Main(string[] args)
        ...{
            ShapeList<Rectangle> rect = new ShapeList<Rectangle>();
            rect.ShowArea(new Rectangle(3, 6));
            ShapeList<Triangle> tri = new ShapeList<Triangle>();
            tri.ShowArea(new Triangle(3, 6));
            ShapeList<SolidLine> line = new ShapeList<SolidLine>();
            line.ShowArea(new SolidLine(5));
            Console.ReadLine();
        }
    }

    class ShapeList<T> where T : IShape
    ...{
        public void ShowArea(T item)
        ...{
            Console.WriteLine("Area is {0}", item.Area()); 
        }
    }
    interface IShape
    ...{
        double Area();
    }
    class Rectangle : IShape
    ...{
        public double length;
        public double width;
        public Rectangle(double length, double width)
        ...{
            this.length = length;
            this.width = width;
        }
           
        public double Area()
        ...{
            return this.length * this.width;
        }
    }
    class Triangle : IShape
    ...{
        public double length;
        public double height;
        public Triangle(double length, double height)
        ...{
            this.length = length;
            this.height = height;
        }
        public double Area()
        ...{
            return this.length * this.height / 2;
        }
    }
    class SolidLine
    ...{
        public double length;
        public SolidLine(double length)
        ...{
            this.length = length;
        }
    }
}