Strategy 战略设计模式

将程序中负责判断（if)等的算法独立出来，组成一个单独的类。或者说将战略部单独封装，以方便在程序中随时转换战略部分，这就是Strategy设计模式。
设想有一个类Human，它有Name,Age,Hight,Weight等属性。如下：

 class Human
    {
       
        private string _name;
        public string Name { get;set;}
        private int _age = -1;
        public int Age { get;set;}
        private int _hight = -1;
        public int Hight { get;set;}
        private int _weight = -1;
        public int Weight { get;set;}

        public Human(string name, int age, int hight, int weight)
        {
            _name = name;
            _age = age;
            _hight = hight;
            _weight = weight;
        }
    }

现在要写一个对2个Human实例比较的类MyClass，如下：

    class MyClass
    {
        int _comparetype = -1;
        public void SetCompareType(int type)
        {
            _comparetype = type;
        }
        public int Compare(Human h1, Human h2)
        {
            if (_comparetype == 1)//年龄par             
  {
                if (h1.Age > h2.Age)
                {
                    return 1;
                }
                else if (h1.Age < h2.Age)
                {
                    return -1;
                }
                else
                    return 0;
            }
            if (_comparetype == 2) //体重
            {
                //・・・・
            }
        }
    }

这里，Compare这个方法非常复杂，可以看作是MyClass的战略部分，我们希望将这部分独立出来，写成下面的方式：

    public class Human
    {

        private string _name;
        public string Name { get { return _name; } set { _name = value; } }
        private int _age = -1;
        public int Age { get { return _age; } set { _age = value; } }
        private int _height = -1;
        public int Height { get { return _height; } set { _height = value; } }
        private int _weight = -1;
        public int Weight { get { return _weight; } set { _weight = value; } }

        public Human(string name, int age, int hight, int weight)
        {
            _name = name;
            _age = age;
            _height = hight;
            _weight = weight;
        }
    }
    //战略部接口
    public interface Comparator
    {
        int compare(Human h1, Human h2);
    }
    public class AgeComparator : Comparator
    {
        public int compare(Human h1, Human h2)
        {
            if (h1.Age > h2.Age)
            {
                return 1;
            }
            else if (h1.Age == h2.Age)
            {
                return 0;
            }
            else
            {
                return -1;
            }
        }
    }
    public class HeightComparator : Comparator
    {
        public int compare(Human h1, Human h2)
        {
            if (h1.Height > h2.Height)
            {
                return 1;
            }
            else if (h1.Height == h2.Height)
            {
                return 0;
            }
            else
            {
                return -1;
            }
        }

    public class MyClass
    {
        private Comparator comparator = null;
        public MyClass(Comparator comparator)
        {
            this.comparator = comparator;
        }
        public int compare(Human h1, Human h2)
        {
            return comparator.compare(h1, h2);
        }
    }
    class ProgramTest
    {
        static void Main(string[] args)
        {
            Human h1 = new Human("Tom", 21, 178, 60);
            Human h2 = new Human("Jack", 22, 268, 56);
            AgeComparator a = new AgeComparator();
            MyClass m = new MyClass(a);
            int i = m.compare(h1, h2);


            Console.WriteLine("比较结果：" + i);
        }
    }
   }

这样，比较接口始终一致，只要替换战略部分：重写接口Comparator,就能实现不同战略的比较。