【设计模式学习笔记】工厂模式

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实现简单计算器

简单工厂模式

类图：
这里写图片描述

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：
这里写图片描述

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

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