多态重构条件语句

首先，在C#中，多态的体现是什么？虚函数、抽象方法、接口。废话不多说，直接上代码：

#region 多态重构switch...case....

    public abstract class ShippingCalculation
    {
        public abstract decimal Calculate();
    }

    public class AlaskShippingCalculation : ShippingCalculation
    {
        public override decimal Calculate()
        {
            return 15m;
        }
    }

    public class NewYorkShippingCalculation : ShippingCalculation
    {
        public override decimal Calculate()
        {
            return 10m;
        }
    }

    public class FloridaShippingCalculation : ShippingCalculation
    {
        public override decimal Calculate()
        {
            return 3m;
        }
    }

    public class Context
    {
        public decimal ProcessCalculate(ShippingCalculation shippingCalculation)
        {
            return shippingCalculation.Calculate();
        }
    }

    #endregion#reg