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);		
	}

	@Override
	public 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);
	}

	@Override
	public 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);
	}

	@Override
	public 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);
	}

	@Override
	public 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.");
		
	}
}

评论

2 楼 rich8w 2009-08-10  

jmu 写道

听说java中双重检查成例不成立  见lz的 OperationFactory的line26

谢谢，我特意去查了双重检查单例，看了http://www.ibm.com/developerworks/cn/java/j-dcl.html的讲解，
原来我这个OperationFactory根本不应该用单例，因为每次加减乘除的参数都可以是不一样的，如果用了单例那每次运算的结果都是一样的。根本是错的。

1 楼 jmu 2009-08-09  

听说java中双重检查成例不成立  见lz的 OperationFactory的line26