学步园

本篇介绍了在JAVA中如何对double或者float的浮点数进行精度计算，在JAVA中提供了多种参数来实现精度的不同控制方式。具体例子如下：

/*<br /> * Created on 2005-6-5<br /> * Author stephen<br /> * Email zhoujianqiang AT gmail DOT com<br /> * CopyRight(C)2005-2008 , All rights reserved.<br /> */<br /> package com.soft4j.utility;<br /> import java.math.BigDecimal;<br /> /**<br /> * 与小数位精度(四舍五入等)相关的一些常用工具方法.<br /> *<br /> * float/double的精度取值方式分为以下几种: <br><br /> * java.math.BigDecimal.ROUND_UP <br><br /> * java.math.BigDecimal.ROUND_DOWN <br><br /> * java.math.BigDecimal.ROUND_CEILING <br><br /> * java.math.BigDecimal.ROUND_FLOOR <br><br /> * java.math.BigDecimal.ROUND_HALF_UP<br><br /> * java.math.BigDecimal.ROUND_HALF_DOWN <br><br /> * java.math.BigDecimal.ROUND_HALF_EVEN <br><br /> *<br /> * @author stephen<br /> * @version 1.0.0<br /> */<br /> public final class RoundTool {<br /> /**<br /> * 对double数据进行取精度.<br /> * <p><br /> * For example: <br><br /> * double value = 100.345678; <br><br /> * double ret = round(value,4,BigDecimal.ROUND_HALF_UP); <br><br /> * ret为100.3457 <br><br /> *<br /> * @param value<br /> * double数据.<br /> * @param scale<br /> * 精度位数(保留的小数位数).<br /> * @param roundingMode<br /> * 精度取值方式.<br /> * @return 精度计算后的数据.<br /> */<br /> public static double round(double value, int scale, int roundingMode) {<br /> BigDecimal bd = new BigDecimal(value);<br /> bd = bd.setScale(scale, roundingMode);<br /> double d = bd.doubleValue();<br /> bd = null;<br /> return d;<br /> }<br /> /**<br /> * 测试用的main方法.<br /> *<br /> * @param argc<br /> * 运行参数.<br /> */<br /> public static void main(String[] argc) {<br /> //下面都以保留2位小数为例</p> <p> //ROUND_UP<br /> //只要第2位后面存在大于0的小数，则第2位就+1<br /> System.out.println(round(12.3401,2,BigDecimal.ROUND_UP));//12.35<br /> System.out.println(round(-12.3401,2,BigDecimal.ROUND_UP));//-12.35<br /> //ROUND_DOWN<br /> //与ROUND_UP相反<br /> //直接舍弃第2位后面的所有小数<br /> System.out.println(round(12.349,2,BigDecimal.ROUND_DOWN));//12.34<br /> System.out.println(round(-12.349,2,BigDecimal.ROUND_DOWN));//-12.34<br /> //ROUND_CEILING<br /> //如果数字>0 则和ROUND_UP作用一样<br /> //如果数字<0 则和ROUND_DOWN作用一样<br /> System.out.println(round(12.3401,2,BigDecimal.ROUND_CEILING));//12.35<br /> System.out.println(round(-12.349,2,BigDecimal.ROUND_CEILING));//-12.34<br /> //ROUND_FLOOR<br /> //如果数字>0 则和ROUND_DOWN作用一样<br /> //如果数字<0 则和ROUND_UP作用一样<br /> System.out.println(round(12.349,2,BigDecimal.ROUND_FLOOR));//12.34<br /> System.out.println(round(-12.3401,2,BigDecimal.ROUND_FLOOR));//-12.35<br /> //ROUND_HALF_UP [这种方法最常用]<br /> //如果第3位数字>=5,则第2位数字+1<br /> //备注:只看第3位数字的值,不会考虑第3位之后的小数的<br /> System.out.println(round(12.345,2,BigDecimal.ROUND_HALF_UP));//12.35<br /> System.out.println(round(12.3449,2,BigDecimal.ROUND_HALF_UP));//12.34<br /> System.out.println(round(-12.345,2,BigDecimal.ROUND_HALF_UP));//-12.35<br /> System.out.println(round(-12.3449,2,BigDecimal.ROUND_HALF_UP));//-12.34<br /> //ROUND_HALF_DOWN<br /> //如果第3位数字>=5,则做ROUND_UP<br /> //如果第3位数字<5,则做ROUND_DOWN<br /> System.out.println(round(12.345,2,BigDecimal.ROUND_HALF_DOWN));//12.35<br /> System.out.println(round(12.3449,2,BigDecimal.ROUND_HALF_DOWN));//12.34<br /> System.out.println(round(-12.345,2,BigDecimal.ROUND_HALF_DOWN));//-12.35<br /> System.out.println(round(-12.3449,2,BigDecimal.ROUND_HALF_DOWN));//-12.34<br /> //ROUND_HALF_EVEN<br /> //如果第3位是偶数,则做ROUND_HALF_DOWN<br /> //如果第3位是奇数,则做ROUND_HALF_UP<br /> System.out.println(round(12.346,2,BigDecimal.ROUND_HALF_EVEN));//12.35<br /> System.out.println(round(12.345,2,BigDecimal.ROUND_HALF_EVEN));//12.35<br /> }<br /> }<br />