典型重构6 (多态)

用多态替换条件
　　3中交通工具

public class Car : Vehicle
{
    public int AmountOfFuelNeededToFillTank()
    {
        return 12;
    }
}
public class Airplane : Vehicle
{
    public int AmountOfFuelNeededToFillLeftFuelTank()
    {
        return 3;
    }
    public int AmountOfFuelNeededToFillRightFuelTank()
    {
        return 4;
    }
}
public class Boat : Vehicle
{
    public int AmountOfFuelNeededToFillFrontFuelTank()
    {
        return 8;
    }
    public int AmountOfFuelNeededToFillRearFuelTank()
    {
        return 10;
    }
}

检查加油车路线上所有车辆以确定要在该加油车内装多少燃料

public class FuelingStation
{
    public int AddFuelToTruck(List<Vehicle> vehiclesOnRoute)
    {
        var amountOfFuelToLoadOnTruck=0;
        foreach(var vehicle in vehiclesOnRoute)
        {
            if(vehicle is Car)
            {
                amountOfFuelToLoadOnTruck+=((Car)vehicle).AmountOfFuelNeededToFillTank();
            }
            else if(vehicle is Airplane)
            {
                amountOfFuelToLoadOnTruck+=((Airplane)vehicle).AmountOfFuelNeededToFillLeftFuelTank();
                amountOfFuelToLoadOnTruck+=((Airplane)vehicle).AmountOfFuelNeededToFillRightFuelTank();
            }
            else if(vehicle is Boat)
            {
                amountOfFuelToLoadOnTruck+=((Boat)vehicle).AmountOfFuelNeededToFillFrontFuelTank();
                amountOfFuelToLoadOnTruck+=((Boat)vehicle).AmountOfFuelNeededToFillRearFuelTank();
            }
        }
        return amountOfFuelToLoadOnTruck;
    }
}

使用动态性对这一方法进行重构,一避免用到交通工具类型的隐秘信息

public interface IFuelable
{
    int GetTotalAmountOfFuelNeededForVehicle();
}

针对Vehicle类实现该接口

public class Car : Vehicle,IFuelable
{
    public int GetTotalAmountOfFuelNeededForVehicle()
    {
        return AmountOfFuelNeededToFillTank();
    }
}
public class Airplane : Vehicle,IFuelable
{
    public int GetTotalAmountOfFuelNeededForVehicle()
    {
        return AmountOfFuelNeededToFillLeftFuelTank()+AmountOfFuelNeededToFillRightFuelTank();
    }
}
public class Boat : Vehicle,IFuelable
{
    public int GetTotalAmountOfFuelNeededForVehicle()
    {

        return AmountOfFuelNeededToFillFrontFuelTank()+AmountOfFuelNeededToFillRearFuelTank();
    }
}

重构结果：

public class FuelingStation
{
    public int AddFuelToTruck(List<Vehicle> vehiclesOnRoute)
    {
        var amountOfFuelToLoadOnTruck=0;
        foreach(var vehicle in vehiclesOnRoute)
        {
            amountOfFuelToLoadOnTruck+=vehicle.GetTotalAmountOfFuelNeededForVehicle();
        }
        return amountOfFuelToLoadOnTruck;
    }
}

或者利用LINQ功能

public int AddFuelToTruck(List<Vehicle> vehiclesOnRoute)
    {
        return vehiclesOnRoute.Sum(vehicle=>vehicle.GetTotalAmountOfFuelNeededForVehicle());
    }