实现简单计算器

简单工厂模式

类图：

代码：

    //运算类
    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;
        }
    }

    //加法运算
    class OperationAdd:Operation
    {
        public override double GetResult() {
            double result = 0;
            result = NumberA + NumberB;
            return result;
        }
    }
    //减法、乘法。。类似

    //运算工厂类
    public class OperationFactory
    {
        public static Operation createOperate(string operate) {
            Operation oper = null;
            switch (operate) {
                case "+":
                    oper = new OperationAdd();
                    break;
                case "-":
                    oper = new OperationSub();
                    break;
                default:
                    break;
            }

            return oper;
        }
    }

    //客户端代码
    Operation oper;
    oper = OperationFactory.createOperate("+");
    oper.NumberA = 1;
    oper.NumberB = 2;
    double result = oper.GetResult();

工厂方法模式

类图：

代码：

//运算类
    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;
        }
    }

    //加法运算
    class OperationAdd:Operation
    {
        public override double GetResult() {
            double result = 0;
            result = NumberA + NumberB;
            return result;
        }
    }
    //工厂接口
    interface IFactory
    {
        Operation CreateOperation();
    }

    //加法运算工厂
    class AddFactory : IFactory
    {
        public Operation CreateOperation() {
            return new OperationAdd();
        }
    }
    //减法、乘法、除法类似

    //客户端代码
    IFactory operFactory = new AddFactory();
    Operation oper = operFactory.CreateOperation();
    oper.NumberA = 1;
    oper.NumberB = 2;
    double result = oper.GetResult();

两种模式对比

工厂方法模式的定义：定义一个用于创建对象的接口，让子类决定实例化哪一个类。工厂方法使一个类的实例化延迟到其子类
简单工程模式的最大优点在于工厂类中包含了必要的逻辑判断，根据客户端的选择条件动态实例化相关的类，对于客户端来说，去除了与具体产品的依赖

工厂方法克服了简单工厂违背开放-封闭原则的缺点，又保持了封装对象创建过程的优点

开放-封闭原则 是说软件实体（类、模块、函数等等）应该可以扩展，但是不可修改

参考：
《大话设计模式》-----程杰