JAVA中double格式化控制精度小数位数，float同理

Java中如何对浮点数进行精度控制，在JAVA中提供了多种参数来实现精度的不同控制方式。以double为例，float同理

转自http://stephen830.iteye.com/blog/260776

Java代码

    /* 
     * Created on 2005-6-5 
     * Author stephen 
     * Email zhoujianqiang AT gmail DOT com 
     * CopyRight(C)2005-2008 , All rights reserved. 
     */  
    package com.soft4j.utility;  

    import java.math.BigDecimal;  

    /** 
     * 与小数位精度(四舍五入等)相关的一些常用工具方法. 
     *  
     * float/double的精度取值方式分为以下几种: 
 
     * java.math.BigDecimal.ROUND_UP 
 
     * java.math.BigDecimal.ROUND_DOWN 
 
     * java.math.BigDecimal.ROUND_CEILING 
 
     * java.math.BigDecimal.ROUND_FLOOR 
 
     * java.math.BigDecimal.ROUND_HALF_UP
 
     * java.math.BigDecimal.ROUND_HALF_DOWN 
 
     * java.math.BigDecimal.ROUND_HALF_EVEN 
 
     *  
     * @author stephen 
     * @version 1.0.0 
     */  
    public final class RoundTool {  

        /** 
         * 对double数据进行取精度. 
         * 
 
         * For example: 
 
         * double value = 100.345678; 
 
         * double ret = round(value,4,BigDecimal.ROUND_HALF_UP); 
 
         * ret为100.3457 
 
         *  
         * @param value 
         *            double数据. 
         * @param scale 
         *            精度位数(保留的小数位数). 
         * @param roundingMode 
         *            精度取值方式. 
         * @return 精度计算后的数据. 
         */  
        public static double round(double value, int scale, int roundingMode) {  
            BigDecimal bd = new BigDecimal(value);  
            bd = bd.setScale(scale, roundingMode);  
            double d = bd.doubleValue();  
            bd = null;  
            return d;  
        }  

        /** 
         * 测试用的main方法. 
         *  
         * @param argc 
         *            运行参数. 
         */  
        public static void main(String[] argc) {  
            //下面都以保留2位小数为例  

            //ROUND_UP  
            //只要第2位后面存在大于0的小数，则第2位就+1  
            System.out.println(round(12.3401,2,BigDecimal.ROUND_UP));//12.35  
            System.out.println(round(-12.3401,2,BigDecimal.ROUND_UP));//-12.35  
            //ROUND_DOWN  
            //与ROUND_UP相反  
            //直接舍弃第2位后面的所有小数  
            System.out.println(round(12.349,2,BigDecimal.ROUND_DOWN));//12.34  
            System.out.println(round(-12.349,2,BigDecimal.ROUND_DOWN));//-12.34  
            //ROUND_CEILING  
            //如果数字>0 则和ROUND_UP作用一样  
            //如果数字<0 则和ROUND_DOWN作用一样  
            System.out.println(round(12.3401,2,BigDecimal.ROUND_CEILING));//12.35  
            System.out.println(round(-12.349,2,BigDecimal.ROUND_CEILING));//-12.34  
            //ROUND_FLOOR  
            //如果数字>0 则和ROUND_DOWN作用一样  
            //如果数字<0 则和ROUND_UP作用一样  
            System.out.println(round(12.349,2,BigDecimal.ROUND_FLOOR));//12.34  
            System.out.println(round(-12.3401,2,BigDecimal.ROUND_FLOOR));//-12.35  
            //ROUND_HALF_UP [这种方法最常用]  
            //如果第3位数字>=5,则第2位数字+1  
            //备注:只看第3位数字的值,不会考虑第3位之后的小数的  
            System.out.println(round(12.345,2,BigDecimal.ROUND_HALF_UP));//12.35  
            System.out.println(round(12.3449,2,BigDecimal.ROUND_HALF_UP));//12.34  
            System.out.println(round(-12.345,2,BigDecimal.ROUND_HALF_UP));//-12.35  
            System.out.println(round(-12.3449,2,BigDecimal.ROUND_HALF_UP));//-12.34  
            //ROUND_HALF_DOWN  
            //如果第3位数字>=5,则做ROUND_UP  
            //如果第3位数字<5,则做ROUND_DOWN  
            System.out.println(round(12.345,2,BigDecimal.ROUND_HALF_DOWN));//12.35  
            System.out.println(round(12.3449,2,BigDecimal.ROUND_HALF_DOWN));//12.34  
            System.out.println(round(-12.345,2,BigDecimal.ROUND_HALF_DOWN));//-12.35  
            System.out.println(round(-12.3449,2,BigDecimal.ROUND_HALF_DOWN));//-12.34  
            //ROUND_HALF_EVEN  
            //如果第3位是偶数,则做ROUND_HALF_DOWN  
            //如果第3位是奇数,则做ROUND_HALF_UP  
            System.out.println(round(12.346,2,BigDecimal.ROUND_HALF_EVEN));//12.35  
            System.out.println(round(12.345,2,BigDecimal.ROUND_HALF_EVEN));//12.35  
        }  
    }