《大话设计模式》阅读笔记和总结。原书是C#编写的，本人用Java实现了一遍，包括每种设计模式的UML图实现和示例代码实现。

目录：

Github地址：

定义：通过一个单独的类来做创造实例的过程，这就是工厂

例子：用程序实现输入两个数和运算符号，得到结果。

分析：这个题目并不难，需要考虑的是需要通过面向对象编程来简化代码，降低耦合度，同时又便于修改和复用。因此这里我们用简单工程模式来实现这个功能。

UML图：

简单工厂模式UML图.png

代码：

运算类

public abstract class Operation {    private double numberA;    private double numberB;    public double getNumberA() {        return numberA;    }    public void setNumberA(double numberA) {        this.numberA = numberA;    }    public double getNumberB() {        return numberB;    }    public void setNumberB(double numberB) {        this.numberB = numberB;    }    public abstract double getResult();}

加法类，继承运算类

public class OperationAdd extends Operation {    @Override    public double getResult() {        double result = getNumberA() + getNumberB();        return result;    }}

减法类，继承运算类

public class OperationSub extends Operation {    @Override    public double getResult() {        double result = getNumberA() - getNumberB();        return result;    }}

乘法类，继承运算类

public class OperationMul extends Operation {    @Override    public double getResult() {        double result = getNumberA() * getNumberB();        return result;    }}

除法类，继承运算类

public class OperationDiv extends Operation {    @Override    public double getResult(){        double result = 0;        try {            if (getNumberB() == 0){                throw new Exception("除数不能为0");            }else {                result = getNumberA() / getNumberB();            }        } catch (Exception e) {            e.printStackTrace();        }        return result;    }}

简单运算工厂类

public class OperationFactory {    public static Operation createOperation(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;            default:                break;        }        return oper;    }}

客户端调用

public class Main {    public static void main(String[] args){        Operation oper = OperationFactory.createOperation("*");        oper.setNumberA(5);        oper.setNumberB(3);        double result = oper.getResult();        System.out.println(result);    }}