我是靠谱客的博主 快乐铃铛，最近开发中收集的这篇文章主要介绍BigDecimal通过setScale设置小数位数发生ArithmeticException，觉得挺不错的，现在分享给大家，希望可以做个参考。
概述
一、前言
通常进行数值计算时，我们会先将double或float等转为BigDecimal再处理，然后对计算结果通过setScale方法取指定的小数位；但是在这里有时会遇到java.lang.ArithmeticException: Rounding necessary，下面我们会对此问题进行演示和说明。
二、代码示例
1. 这里以double转BigDecimal后获取不同小数位值来举例说明，具体如下：
package com.dz.config;
import java.math.BigDecimal;
import java.math.RoundingMode;
/**
* @author alen
* @create 2018-11-01 17:39
**/
public class t {
public static void main(String[] args) {
double d = 10.0000000001;
String s = "10.0000000001";
BigDecimal newBigDecimal = new BigDecimal(d);
BigDecimal newStringBigDecimal = new BigDecimal(s);
BigDecimal valueOfBigDecimal = BigDecimal.valueOf(d);
// newBigDecimal===================================
System.out.println("newBigDecimal's scale:" + newBigDecimal.scale());
try {
System.out.println("newBigDecimal setScale(50):" + newBigDecimal.setScale(50));
} catch (Exception e) {
System.out.println("newBigDecimal setScale(50):" + e);
}
try {
System.out.println("newBigDecimal setScale(49):" + newBigDecimal.setScale(49));
} catch (Exception e) {
System.out.println("newBigDecimal setScale(49):" + e);
}
try {
System.out.println("newBigDecimal setScale(48):" + newBigDecimal.setScale(48));
} catch (Exception e) {
System.out.println("newBigDecimal setScale(48):" + e);
System.out.println("newBigDecimal setScale(48, RoundingMode.HALF_UP):" + newBigDecimal.setScale(48, RoundingMode.HALF_UP));
}
// valueOfBigDecimal======================================
System.out.println("valueOfBigDecimal's scale:" + valueOfBigDecimal.scale());
try {
System.out.println("valueOfBigDecimal setScale(50):" + valueOfBigDecimal.setScale(50));
} catch (Exception e) {
System.out.println("valueOfBigDecimal setScale(50):" + e);
}
try {
System.out.println("valueOfBigDecimal setScale(49):" + valueOfBigDecimal.setScale(49));
} catch (Exception e) {
System.out.println("valueOfBigDecimal setScale(49):" + e);
}
try {
System.out.println("valueOfBigDecimal setScale(48):" + valueOfBigDecimal.setScale(48));
} catch (Exception e) {
System.out.println("valueOfBigDecimal setScale(48):" + e);
System.out.println("valueOfBigDecimal setScale(48, RoundingMode.HALF_UP):" + valueOfBigDecimal.setScale(48, RoundingMode.HALF_UP));
}
// newStringBigDecimal======================================
System.out.println("newStringBigDecimal's scale:" + newStringBigDecimal.scale());
try {
System.out.println("newStringBigDecimal setScale(50):" + newStringBigDecimal.setScale(50));
} catch (Exception e) {
System.out.println("newStringBigDecimal setScale(50):" + e);
}
try {
System.out.println("newStringBigDecimal setScale(49):" + newStringBigDecimal.setScale(49));
} catch (Exception e) {
System.out.println("newStringBigDecimal setScale(49):" + e);
}
try {
System.out.println("newStringBigDecimal setScale(48):" + newStringBigDecimal.setScale(48));
} catch (Exception e) {
System.out.println("newStringBigDecimal setScale(48):" + e);
System.out.println("newStringBigDecimal setScale(48, RoundingMode.HALF_UP):" + newStringBigDecimal.setScale(48, RoundingMode.HALF_UP));
}
d = 10.01;
s = "10.01";
newBigDecimal = new BigDecimal(d);
valueOfBigDecimal = BigDecimal.valueOf(d);
newStringBigDecimal = new BigDecimal(s);
// newBigDecimal==========================================
System.out.println("newBigDecimal's scale:" + newBigDecimal.scale());
try {
System.out.println("newBigDecimal setScale(3):" + newBigDecimal.setScale(3));
} catch (Exception e) {
System.out.println("newBigDecimal setScale(3):" + e);
System.out.println("newBigDecimal setScale(3, RoundingMode.HALF_UP):" + newBigDecimal.setScale(3, RoundingMode.HALF_UP));
}
try {
System.out.println("newBigDecimal setScale(2):" + newBigDecimal.setScale(2));
} catch (Exception e) {
System.out.println("newBigDecimal setScale(2):" + e);
System.out.println("newBigDecimal setScale(2, RoundingMode.HALF_UP):" + newBigDecimal.setScale(2, RoundingMode.HALF_UP));
}
try {
System.out.println("newBigDecimal setScale(1):" + newBigDecimal.setScale(1));
} catch (Exception e) {
System.out.println("newBigDecimal setScale(1):" + e);
System.out.println("newBigDecimal setScale(1, RoundingMode.HALF_UP):" + newBigDecimal.setScale(1, RoundingMode.HALF_UP));
}
// valueOfBigDecimal======================================
System.out.println("valueOfBigDecimal's scale:" + valueOfBigDecimal.scale());
try {
System.out.println("valueOfBigDecimal setScale(3):" + valueOfBigDecimal.setScale(3));
} catch (Exception e) {
System.out.println("valueOfBigDecimal setScale(3):" + e);
}
try {
System.out.println("valueOfBigDecimal setScale(2):" + valueOfBigDecimal.setScale(2));
} catch (Exception e) {
System.out.println("valueOfBigDecimal setScale(2):" + e);
}
try {
System.out.println("valueOfBigDecimal setScale(1):" + valueOfBigDecimal.setScale(1));
} catch (Exception e) {
System.out.println("valueOfBigDecimal setScale(1):" + e);
System.out.println("valueOfBigDecimal setScale(1, RoundingMode.HALF_UP):" + valueOfBigDecimal.setScale(1, RoundingMode.HALF_UP));
}
//
// newStringBigDecimal======================================
System.out.println("newStringBigDecimal's scale:" + newStringBigDecimal.scale());
try {
System.out.println("newStringBigDecimal setScale(3):" + newStringBigDecimal.setScale(3));
} catch (Exception e) {
System.out.println("newStringBigDecimal setScale(3):" + e);
}
try {
System.out.println("newStringBigDecimal setScale(2):" + newStringBigDecimal.setScale(2));
} catch (Exception e) {
System.out.println("newStringBigDecimal setScale(2):" + e);
}
try {
System.out.println("newStringBigDecimal setScale(1):" + newStringBigDecimal.setScale(1));
} catch (Exception e) {
System.out.println("newStringBigDecimal setScale(1):" + e);
System.out.println("newStringBigDecimal setScale(1, RoundingMode.HALF_UP):" + newStringBigDecimal.setScale(1, RoundingMode.HALF_UP));
}
}
}
运算结果如下：
newBigDecimal's scale:49
newBigDecimal setScale(50):10.00000000010000000827403709990903735160827636718750
newBigDecimal setScale(49):10.0000000001000000082740370999090373516082763671875
newBigDecimal setScale(48):java.lang.ArithmeticException: Rounding necessary
newBigDecimal setScale(48, RoundingMode.HALF_UP):10.000000000100000008274037099909037351608276367188
valueOfBigDecimal's scale:10
valueOfBigDecimal setScale(50):10.00000000010000000000000000000000000000000000000000
valueOfBigDecimal setScale(49):10.0000000001000000000000000000000000000000000000000
valueOfBigDecimal setScale(48):10.000000000100000000000000000000000000000000000000
newStringBigDecimal's scale:10
newStringBigDecimal setScale(50):10.00000000010000000000000000000000000000000000000000
newStringBigDecimal setScale(49):10.0000000001000000000000000000000000000000000000000
newStringBigDecimal setScale(48):10.000000000100000000000000000000000000000000000000
newBigDecimal's scale:49
newBigDecimal's value:10.0099999999999997868371792719699442386627197265625
newBigDecimal setScale(3):java.lang.ArithmeticException: Rounding necessary
newBigDecimal setScale(3, RoundingMode.HALF_UP):10.010
newBigDecimal setScale(2):java.lang.ArithmeticException: Rounding necessary
newBigDecimal setScale(2, RoundingMode.HALF_UP):10.01
newBigDecimal setScale(1):java.lang.ArithmeticException: Rounding necessary
newBigDecimal setScale(1, RoundingMode.HALF_UP):10.0
valueOfBigDecimal's scale:2
valueOfBigDecimal setScale(3):10.010
valueOfBigDecimal setScale(2):10.01
valueOfBigDecimal setScale(1):java.lang.ArithmeticException: Rounding necessary
valueOfBigDecimal setScale(1, RoundingMode.HALF_UP):10.0
newStringBigDecimal's scale:2
newStringBigDecimal setScale(3):10.010
newStringBigDecimal setScale(2):10.01
newStringBigDecimal setScale(1):java.lang.ArithmeticException: Rounding necessary
newStringBigDecimal setScale(1, RoundingMode.HALF_UP):10.02. 结果分析：
通过运行结果我们会发现两种情况：
①通过new直接将double作为参数传入得到的值输出后并不等于原double值，传入string或valueOf方法得到的结果等于原值；
事实上查看Java文档会发现有三种方式将double转为BigDecimal：
1. new BigDecimal(double d)；
2. new BigDecimal(String s)；
3.BigDecimal.valueOf(double d) ；
第一种是double的二进制形式的结果，所以BigDecimal的值并不一定为其原值，如上代码所示：10.0000000001转换后为10.0000000001000000082740370999090373516082763671875 ，共有49位小数（不同机器结果会不同），10.01转换后为10.0099999999999997868371792719699442386627197265625，第二种和第三种结果相同，仍然为原值，因为第三种相当于先将double转为String（Double.toString(double)）。
②同时我们会发现，设置结果小数位数小于当前位数时，如果未设置进位方式会抛出异常：java.lang.ArithmeticException: Rounding necessary，提示我们进位方式必须，当我们设置四舍五入后即可，其他方式可查看RoundingMode枚举类。
三、结论：
通过上述分析，我们可以看出当对BigDecimal的值进位时需指定进位方式，否则会发生java.lang.ArithmeticException: Rounding necessary。
最后
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