oop - 如何将组合与继承结合使用？

Question

我将尝试在一个简单的例子中提出我的问题......

假设我有一个抽象基类 Car。汽车有一个基本的引擎对象。我在抽象 Car 类中有一个方法 StartEngine() ，它将引擎的启动委托(delegate)给 Engine 对象。

如何允许 Car 的子类(例如 Ferrari)将 Engine 对象声明为特定类型的引擎(例如 TurboEngine)？我需要另一个汽车类(TurboCar)吗？

我继承了一个普通的旧 Engine 对象，我无法在我的 Car 子类中将它重新声明(或覆盖)为 TurboEngine。

编辑:我知道我可以将 Engine 的任何子类插入到我的 Ferrari 类中的 myEngine 引用中......但是我如何调用只有 TurboEngine 公开的方法？因为 myEngine 是作为基础引擎继承的，所以不包括任何涡轮增压的东西。

谢谢!

Answer 1

抽象工厂模式正是针对这个问题。 Google GoF Abstract Factory {您的首选语言}

在下文中，请注意如何使用具体工厂来生成“完整”对象(enzo、civic)或使用它们来生成相关对象的“族”(CarbonFrame + TurboEngine、WeakFrame + WeakEngine)。最终，您总是会得到一个 Car 对象，该对象以特定类型的行为响应Accelerator()。

     using System;


    abstract class CarFactory
    {
        public static CarFactory FactoryFor(string manufacturer){
            switch(manufacturer){
                case "Ferrari" : return new FerrariFactory();
                case "Honda" : return new HondaFactory();
                default:
                    throw new ArgumentException("Unknown car manufacturer. Please bailout industry.");
            }
        }

        public abstract Car createCar();
        public abstract Engine createEngine();
        public abstract Frame createFrame();

    }

    class FerrariFactory : CarFactory
    {
        public override Car createCar()
        {
            return new Ferrari(createEngine(), createFrame());
        }

        public override Engine createEngine()
        {
            return new TurboEngine();
        }

        public override Frame createFrame()
        {
            return new CarbonFrame();
        }
    }

    class HondaFactory : CarFactory
    {
        public override Car createCar()
        {
            return new Honda(createEngine(), createFrame());
        }

        public override Engine createEngine()
        {
            return new WeakEngine();
        }

        public override Frame createFrame()
        {
            return new WeakFrame();
        }
    }

    abstract class Car
    {
        private Engine engine;
        private Frame frame;

        public Car(Engine engine, Frame frame)
        {
            this.engine = engine;
            this.frame = frame;
        }

        public void accelerate()
        {
            engine.setThrottle(1.0f);
            frame.respondToSpeed();
        }

    }

    class Ferrari : Car
    {
        public Ferrari(Engine engine, Frame frame) : base(engine, frame)
        {
            Console.WriteLine("Setting sticker price to $250K");
        }
    }

    class Honda : Car
    {
        public Honda(Engine engine, Frame frame) : base(engine, frame)
        {
            Console.WriteLine("Setting sticker price to $25K");
        }
    }

    class KitCar : Car
    {
        public KitCar(String name, Engine engine, Frame frame)
            : base(engine, frame)
        {
            Console.WriteLine("Going out in the garage and building myself a " + name);
        }
    }

    abstract class Engine
    {
        public void setThrottle(float percent)
        {
            Console.WriteLine("Stomping on accelerator!");
            typeSpecificAcceleration();
        }

        protected abstract void typeSpecificAcceleration();
    }

    class TurboEngine : Engine
    {
        protected override void typeSpecificAcceleration()
        {
            Console.WriteLine("Activating turbo");
            Console.WriteLine("Making noise like Barry White gargling wasps");
        }
    }

    class WeakEngine : Engine
    {
        protected override void typeSpecificAcceleration()
        {
            Console.WriteLine("Provoking hamster to run faster");
            Console.WriteLine("Whining like a dentist's drill");
        }
    }

    abstract class Frame
    {
        public abstract void respondToSpeed();
    }

    class CarbonFrame : Frame
    {
        public override void respondToSpeed()
        {
            Console.WriteLine("Activating active suspension and extending spoilers");
        }
    }

    class WeakFrame : Frame
    {
        public override void respondToSpeed()
        {
            Console.WriteLine("Loosening bolts and vibrating");
        }
    }

    class TestClass
    {
        public static void Main()
        {
            CarFactory ferrariFactory = CarFactory.FactoryFor("Ferrari");
            Car enzo = ferrariFactory.createCar();
            enzo.accelerate();

            Console.WriteLine("---");
            CarFactory hondaFactory = CarFactory.FactoryFor("Honda");
            Car civic = hondaFactory.createCar();
            civic.accelerate();

            Console.WriteLine("---");
            Frame frame = hondaFactory.createFrame();
            Engine engine = ferrariFactory.createEngine();
            Car kitCar = new KitCar("Shaker", engine, frame);
            kitCar.accelerate();

            Console.WriteLine("---");
            Car kitCar2 = new KitCar("LooksGreatGoesSlow", hondaFactory.createEngine(), ferrariFactory.createFrame());
            kitCar2.accelerate();
        }
    }