简单工厂模式

 

    public class Operation
    {
        private double _numberA = 0;
        private double _numberB = 0;

        public double NumberA
        {
            get { return _numberA; }
            set { _numberA = value; }
        }

        public double NumberB
        {
            get { return _numberB; }
            set { _numberB = value; }
        }

        public virtual double GetResult()
        {
            double result = 0;
            return result;
        }
    }

 

    class OperationAdd : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA + NumberB;
            return result;
        }
    }

 

    class OperationSub : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA - NumberB;
            return result;
        }
    }

 

    class OperationMul : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA * NumberB;
            return result;
        }
    }

 

    class OperationDiv : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            if (NumberB == 0)
                throw new Exception("除数不能为0。");
            result = NumberA / NumberB;
            return result;
        }
    }

 

    public class OperationFactory
    {
        public static Operation CreateOperate(string operate)
        {
            Operation oper = null;
            switch (operate)
            { 
                case "+":
                    oper = new OperationAdd();
                    break;
                case "-":
                    oper = new OperationSub();
                    break;
                case "*":
                    oper = new OperationMul();
                    break;
                case "/":
                    oper = new OperationDiv();
                    break;
            }
            return oper;
        }
    }

 

    class Client
    {
        static void Main(string[] args)
        {
            Operation oper;
            oper = OperationFactory.CreateOperate("+");
            oper.NumberA = 1;
            oper.NumberB = 2;
            double result = oper.GetResult();
            Console.WriteLine(result);
        }
    }

 

小结：

• 模式分析：简单工厂模式根据提供给它的数据，返回几个类中的一个类的实例。通常返回的类都有一个公共父类和公共方法。
• 优点：工厂类含有必要的判断逻辑，可以决定在什么时候创建哪一个产品类的实例，客户端可以免除直接创建产品对象的责任，通过这种方法实现了对责任的分割。
• 缺点：工厂类集中了所有产品创建逻辑，一旦不能工作，整个系统都要受到影响。同时，系统扩展困难，一旦添加新产品就不得不修改工厂逻辑。