策略模式

定义： 策略模式定义了一系列算法，并将每个算法封装起来，使他们可以相互替换，且算法的变化不会影响到使用算法的客户。

优点： 1、算法可以自由切换。 2、避免使用多重条件判断。 3、扩展性良好。

缺点： 1、策略类会增多。 2、所有策略类都需要对外暴露。

namespace ConsoleApp1
{
    //定义抽象策略
    public interface IStrategy
    {
         float calc(int num1, int num2);
    }
    //定义具体策略
    //加法
    public class AddStrategy : IStrategy
    {
        public float calc(int num1, int num2)
        {
            return num1 + num2;
        }
    }
    //减法
    public class SubstractStrategy : IStrategy
    {
        public float calc(int num1, int num2)
        {
            return num1 - num2;
        }
    }
    //乘法
    public class MultiplicationStrategy : IStrategy
    {
        public float calc(int num1, int num2)
        {
            return num1 * num2;
        }
    }
    //除法
    public class DivisionStrategy : IStrategy
    {
        public float calc(int num1, int num2)
        {
            return num1 / num2;
        }
    }
    //处理环境
    public class Environment
    {
        private IStrategy strategy;
        public Environment(IStrategy strategy)
        {
            this.strategy = strategy;
        }
        public float calculate(int a, int b)
        {
            return strategy.calc(a, b);
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            Environment environment = new Environment(new AddStrategy());
            float result = environment.calculate(20, 5);
            Console.WriteLine("计算结果：" + result);

            Environment environment1 = new Environment(new SubstractStrategy());
            float result1 = environment1.calculate(20, 5);
            Console.WriteLine("计算结果：" + result1);

            Environment environment2 = new Environment(new MultiplicationStrategy());
            float result2 = environment2.calculate(20, 5);
            Console.WriteLine("计算结果：" + result2);

            Environment environment3 = new Environment(new DivisionStrategy());
            float result3 = environment3.calculate(20, 5);
            Console.WriteLine("计算结果：" + result3);
        }
    }
}