设计模式一——简单工厂模式



一、简单工厂（创建型模式）（不是GOF二十三种设计模式之一）：由一个工厂类根据传入的参数，动态决定应该创建哪一个产品类（产品类继承于父类或者接口）的实例。

二、类图：

三、代码

    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("0不能作为除数");
            result = NumberA / NumberB;
            return result;
        }
    }

//Operation Factory

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

//Main

        /// <summary>
        /// 计算器的代码，实现方法的封装，继承
        /// </summary>
        /// <param name="args"></param>
        static void Main(string[] args)
        {
            Operation oper;
            oper = OperationFactory.createOperate("+");
            oper.NumberA = 10;
            oper.NumberB = 5;
            double result = oper.GetResult();
            Console.WriteLine(result);
            Console.ReadLine();
        }

四、优缺点

优点：

不需要关心如何创建具体的产品，只需要提供产品的名称作为参数传给工厂，就可以实现想要的产品功能，构造容易，逻辑简单

缺点：

1. 调用方法传递参数时，需要switch判断具体实现哪个方法

2. 一个工厂类集合了所有类的实例创建逻辑，违反了高内聚的责任分配原则

引用：http://www.cnblogs.com/ytaozhao/p/3387540.html

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