01_SimpleFactoryPattern 计算器实例
大话设计模式书中摘录语句：
喝酒唱歌，人生真爽。
活字印刷：
1，要改，只需更改要改之字，此为可维护；
2，这些字并非用完这次就无用，完全可以再后来的印刷中重复使用，此乃可复用；
3，若要加字，只需另刻字加入即可，这是可扩展；
4，字的排列其实可能是横排或竖排，只需将活字移动就可满足排列需求，这是灵活性好。

按照里面的第一章，写了个java版的计算器实例，以便自己更深入理解。

Operation抽象类

package cn;import java.math.BigDecimal;public abstract class Operation {protected BigDecimal dcm;protected BigDecimal dcm1;protected BigDecimal dcm2;/** * @param num1 * @param num2 */public Operation(String num1,String num2){dcm1=new BigDecimal(num1.toCharArray());dcm2=new BigDecimal(num2.toCharArray());}public abstract String getResult();}

修改后的OperationFactory，OperationAdd等不能使用单例。

package cn;import cn.beans.OperationAdd;import cn.beans.OperationDiv;import cn.beans.OperationMul;import cn.beans.OperationSub;public class OperationFactory {//这样就不会出现双重检查单例的问题了。private static OperationFactory instance=new OperationFactory();private OperationAdd operationAdd;private OperationSub operationSub;private OperationMul operatoinMul;private OperationDiv operationDiv;public static OperationFactory getInstance() {return instance;}public OperationAdd OperationAdd(String num1,String num2){operationAdd= new OperationAdd(num1,num2);return operationAdd;}public OperationSub OperationSub(String num1,String num2){operationSub= new OperationSub(num1,num2);return operationSub;}public OperationMul OperationMul(String num1,String num2){operatoinMul= new OperationMul(num1,num2);return operatoinMul;}public OperationDiv OperationDiv(String num1,String num2){operationDiv= new OperationDiv(num1,num2);return operationDiv;}}

加法业务Bean类OperationAdd

package cn.beans;import cn.Operation;public class OperationAdd extends Operation {public OperationAdd(String num1, String num2) {super(num1,num2);}@Overridepublic String getResult() {dcm = dcm1.add(dcm2);return dcm.toString();}}

减法业务Bean类OperationSub

package cn.beans;import cn.Operation;public class OperationSub extends Operation{public OperationSub(String num1, String num2) {super(num1, num2);}@Overridepublic String getResult() {dcm = dcm1.subtract(dcm2);return dcm.toString();}}

乘法业务Bean类OperationMul

package cn.beans;import java.math.BigDecimal;import cn.Operation;public class OperationMul extends Operation {public OperationMul(String num1, String num2) {super(num1, num2);}@Overridepublic String getResult() {//setScale(保留小数位数，精确方式);dcm=dcm1.multiply(dcm2).setScale(3, BigDecimal.ROUND_HALF_UP);return dcm.toString();}}

除法业务Bean类OperationDiv

package cn.beans;import java.math.BigDecimal;import cn.Operation;public class OperationDiv extends Operation {public OperationDiv(String num1, String num2) {super(num1, num2);}@Overridepublic String getResult() {if (dcm2.toString().equals("0"))return "除数不能为零";//商=被除数.divide(除数，保留小数位数，精确方法)   dcm=dcm1.divide(dcm2,2,BigDecimal.ROUND_HALF_UP);return dcm.toString();}}

还有最后一个JUnit的测试类

package junit.test;import org.junit.Test;import cn.Operation;import cn.OperationFactory;import cn.beans.OperationDiv;import cn.beans.OperationMul;import cn.beans.OperationSub;public class Test_Calculator {@Test public void test(){/** * 加减乘除 * 测试类 */String str=null;String num1="12.34";String num2="43.21";//Operation operationAdd = OperationFactory.getInstance().OperationAdd(num1, num2);str = operationAdd.getResult();System.err.println("加法结果1："+str);num1="56.78";num2="43.21";Operation operationAdd2 = OperationFactory.getInstance().OperationAdd(num1, num2);str = operationAdd2.getResult();System.err.println("加法结果2："+str);//Operation operationSub = OperationFactory.getInstance().OperationSub(num1, num2);str = operationSub.getResult();System.err.println("减法结果："+str);//Operation operationMul = OperationFactory.getInstance().OperationMul(num1, num2);str = operationMul.getResult();System.err.println("乘法结果："+str);//num1="78.90";num2="90.12";Operation operationMul2 = OperationFactory.getInstance().OperationMul(num1, num2);str = operationMul2.getResult();System.err.println("乘法结果2："+str);//Operation operationDiv = OperationFactory.getInstance().OperationDiv(num1, num2);str = operationDiv.getResult();System.err.println("除法结果："+str);//System.err.println("End.");}}