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java四舍五入自己写_java取四舍五入的方法

JAVA 算法

2023-03-02 11:48:30 时间

“带下划线内容无效"

两种不同方法的实现：

1:/\*\*\* 提供小数位四舍五入处理。\* @param v 需要四舍五入的数字\* @param scale 小数点后保留几位\* @return 四舍五入后的结果\*/public static double round(double v,int scale)\{String temp="\#,\#\#0.";for (int i=0;i;0; i--) \{temp\*=10;\}d\*=temp;long dl=Math.round(d);return (double)(dl)/temp;\}

鉴于网友的的指出，我重新认真研究了一下四舍五入，最终给出正确解法如下：

import java.math.BigDecimal;

import java.text.DecimalFormat;

/\*\*

\* 本例通过对网上几种取四舍五入的研究，进行了一一测试。最终通过实验和理论得出round4为唯一正确的算法。

\* 2008/10/13

\* @author jamezhan

\*/

public class RoundTest \{

public static double round1(double v, int scale) \{

if (scale < 0)

return v;

String temp = "\#\#\#\#\#0.";

for (int i = 0; i < scale; i++) \{

temp += "0";

return Double.valueOf(new java.text.DecimalFormat(temp).format(v));

/\*\*

\* 该算法会出现中间运算后结果超过Double.MAX\_VALUE，所以不推荐使用

\* @param d

\* @param scale

\* @return

\* @throws Exception

\*/

public static double round2(double d, int scale) throws Exception \{

if (scale < 0)

return d;

long temp = 1;

for (int i = scale; i > 0; i--) \{

temp \*= 10;

if (Math.abs(d \* temp) > Double.MAX\_VALUE)

throw new Exception("data is too big or too small");

d \*= temp;

long dl = Math.round(d);

return (double) (dl) / temp;

public static double round3(double v, int scale) \{

BigDecimal value = new BigDecimal(v);

float actualTax = value.setScale(scale, BigDecimal.ROUND\_HALF\_UP).floatValue();

return actualTax;

public static double round4(double v,int scale)

if(scale<0)\{

throw new IllegalArgumentException("The scale must be a positive integer or zero");

BigDecimal b = new BigDecimal(Double.toString(v));

BigDecimal one = new BigDecimal("1");

return b.divide(one,scale,BigDecimal.ROUND\_HALF\_UP).doubleValue();

public static void testRound1(double d, int scale) \{

System.out.println("==========================");

System.out.println("data:"+ d + "; scale:"+scale);

double a = round1(d, scale);

System.out.println(a);

DecimalFormat df = new DecimalFormat();

System.out.println("formatted:"+df.format(a));

public static void testRound2(double d, int scale) \{

try \{

System.out.println("==========================");

System.out.println("data:"+ d + "; scale:"+scale);

double a = round2(d, scale);

System.out.println(a);

DecimalFormat df = new DecimalFormat();

System.out.println("formatted:"+df.format(a));

\} catch (Exception e) \{

System.err.println( e.getMessage() );

public static void testRound3(double d, int scale) \{

try \{

System.out.println("==========================");

System.out.println("data:"+ d + "; scale:"+scale);

double a = round3(d, scale);

System.out.println(a);

DecimalFormat df = new DecimalFormat();

System.out.println("formatted:"+df.format(a));

\} catch (Exception e) \{

System.err.println( e.getMessage() );

public static void testRound4(double d, int scale) \{

try \{

System.out.println("==========================");

System.out.println("data:"+ d + "; scale:"+scale);

double a = round4(d, scale);

System.out.println(a);

DecimalFormat df = new DecimalFormat();

System.out.println("formatted:"+df.format(a));

\} catch (Exception e) \{

System.err.println( e.getMessage() );

public static void main(String\[\] args) throws Exception \{

System.out.println("\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\* Test round1 \*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*");

testRound1(Double.MAX\_VALUE,2);

testRound1(1.264,2);

testRound1(-1.264,2);

testRound1(1.265,2);//wrong result

testRound1(-1.265,2);//wrong result

testRound1(1.266,2);

testRound1(-1.266,2);

testRound1(10224948.265,2);//wrong result

testRound1(-10224948.265,2);//wrong result

testRound1(-Double.MAX\_VALUE, 2);

System.out.println("\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\* Test round2 \*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*");

testRound2(Double.MAX\_VALUE,2);

testRound2(1.264,2);

testRound2(-1.264,2);

testRound2(1.265,2);//wrong result (java表示小数0.1的问题导致的 1.265表示为1.2599999904632568)

testRound2(-1.265,2);//wrong result (由于round算法是先加0.5再运算，所以d为负数时且最后一位小数为5时结果是不正确的)

testRound2(1.266,2);

testRound2(-1.266,2);

testRound2(10224948.265,2);

testRound2(-10224948.265,2);//wrong result

testRound2(-Double.MAX\_VALUE, 2);

System.out.println("\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\* Test round3 \*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*");

testRound3(Double.MAX\_VALUE,2);//wrong result

testRound3(1.264,2);

testRound3(-1.264,2);

testRound3(1.265,2);

testRound3(-1.265,2);

testRound3(1.266,2);

testRound3(-1.266,2);

testRound3(10224948.265,2);//wrong result

testRound3(-10224948.265,2);//wrong result

testRound3(-Double.MAX\_VALUE, 2);//wrong result

System.out.println("\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\* Test round4 \*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*\*");

testRound4(Double.MAX\_VALUE,2);

testRound4(1.264,2);

testRound4(-1.264,2);

testRound4(1.265,2);

testRound4(-1.265,2);

testRound4(1.266,2);

testRound4(-1.266,2);

testRound4(10224948.265,2);

testRound4(-10224948.265,2);

testRound4(-Double.MAX\_VALUE, 2);

posted on 2006-04-25 11:38 翠竹 阅读(12665) 评论(6)  编辑  收藏 所属分类: java

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