设计模式--简单工厂模式
从设计模式的类型上来说，简单工厂模式是属于创建型模式，又叫做静态工厂方法（StaticFactory Method）模式，但不属于23种GOF设计模式之一。简单工厂模式是由一个工厂对象决定创建出哪一种产品类的实例。简单工厂模式是工厂模式家族中最简单实用的模式，可以理解为是不同工厂模式的一个特殊实现。
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实例：面向对象编程实现两个数的四则运算
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运算父类：Operation.java
package factory;public abstract class Operation {public abstract double getResult();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;}protected double numberA = 0;protected double numberB = 0;}运算子类：OperationAdd.java
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package factory;public class OperationAdd extends Operation {@Overridepublic double getResult() {// TODO Auto-generated method stubreturn numberA + numberB;}}?
运算子类：OperationSub.java
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package factory;public class OperationSub extends Operation {@Overridepublic double getResult() {// TODO Auto-generated method stubreturn numberA - numberB;}}??
运算子类：OperationMul.java
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package factory;public class OperationMul extends Operation {@Overridepublic double getResult() {// TODO Auto-generated method stubreturn numberA * numberB;}}??
运算子类：OperationDiv.java
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package factory;public class OperationDiv extends Operation {@Overridepublic double getResult() {// TODO Auto-generated method stubdouble result = 0;try {result = numberA / numberB;} catch (ArithmeticException e) {System.out.println("除数不能为0");}return result;}}?工厂类：OperationFactory.java
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package factory;public class OperationFactory {public static Operation createOperation(String operator) {Operation operation = null;if (operator.equals("+")) {operation = new OperationAdd();} else if (operator.equals("-")) {operation = new OperationSub();} else if (operator.equals("*")) {operation = new OperationMul();} else if (operator.equals("/")) {operation = new OperationDiv();}return operation;}}?Main函数
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package factory;import java.util.Scanner;public class Main {/** * @param args */public static void main(String[] args) {// TODO Auto-generated method stubScanner in = new Scanner(System.in);double numberA;double numberB;String operator;try {System.out.println("请输入数字A：");numberA = in.nextDouble();System.out.println("请输入运算符合(+、-、*、/)：");operator = in.next();System.out.println("请输入数字B：");numberB = in.nextDouble();Operation operation = OperationFactory.createOperation(operator);operation.setNumberA(numberA);operation.setNumberB(numberB);System.out.println("结果是：" + operation.getResult());} catch (Exception e) {System.out.println("输入错误：" + e.getMessage());}}}