简单工厂模式

《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：设计模式
Github地址：DesignPattern

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：

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); } }