需求
業務需要導出的Excel的數字內容保留兩位小數,并且四舍五入
代碼實現
百度一圈所抄襲的代碼
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dfScale2.format(1.125D); |
發現問題
導出數據很詭異.不是所有數據都是如所想的四舍五入.
經過排查最終發現是RoundingMode的問題,應該使用HALF_UP,
DecimalFormat 默認使用的是HALF_EVEN
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DecimalFormat dfScale2 = new DecimalFormat("###.##");System.out.println("dfScale2.getRoundingMode()=" + dfScale2.getRoundingMode());//輸出結果dfScale2.getRoundingMode()=HALF_EVEN// |
RoundingMode.HALF_EVEN
想了解HALF_EVEN，去官網API看了下
HALF_EVEN 被舍位是5(如保留兩位小數的2.115),后面還有非0值進1(如保留兩位小數的2.11500001 格式化為2.12),5后面沒有數字或者都是0時,前面是偶數則舍,是奇數則進1,目標是讓被舍前一位變為偶數.
- CEILING 向更大的值靠近
- Rounding mode to round towards positive infinity.
- DOWN向下取整
- Rounding mode to round towards zero.
- FLOOR 向更小的值靠近
- Rounding mode to round towards negative infinity.
- HALF_DOWN 五舍六入
- Rounding mode to round towards “nearest neighbor” unless both neighbors are equidistant, in which case round down.
- HALF_EVEN
- Rounding mode to round towards the “nearest neighbor” unless both neighbors are equidistant, in which case, round towards the even neighbor.
- HALF_UP 四舍五入
- Rounding mode to round towards “nearest neighbor” unless both neighbors are equidistant, in which case round up.
- UNNECESSARY 設置這個模式,對于精確值格式化會拋出異常
- Rounding mode to assert that the requested operation has an exact result, hence no rounding is necessary.
- UP 向遠離數字0進行進位.
- Rounding mode to round away from zero.
錯誤的代碼測試RoundingMode.HALF_EVEN
為了更好的理解HALF_EVEN,寫了些測試代碼但是發現自己更迷惘了…搞不清楚到底HALF_EVEN是什么機制進舍…輸出結果的尾數很不規律.
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import java.math.BigDecimal;import java.math.RoundingMode;import java.text.DecimalFormat;import java.util.*;public class LocalTest {//定義一個保留兩位小數格式的 DecimalFormat 的變量 dfScale2 @Test public void testDecimalFormat() { DecimalFormat dfScale2 = new DecimalFormat("###.##"); System.out.println("dfScale2.getRoundingMode()=" + dfScale2.getRoundingMode()); System.out.println("dfScale2.format(1.125D)=" + dfScale2.format(1.125D)); System.out.println("dfScale2.format(1.135D)=" + dfScale2.format(1.135D)); System.out.println("dfScale2.format(1.145D)=" + dfScale2.format(1.145D)); System.out.println("dfScale2.format(1.225D)=" + dfScale2.format(1.225D)); System.out.println("dfScale2.format(1.235D)=" + dfScale2.format(1.235D)); System.out.println("dfScale2.format(1.245D)=" + dfScale2.format(1.245D)); System.out.println(); System.out.println("dfScale2.format(2.125D)=" + dfScale2.format(2.125D)); System.out.println("dfScale2.format(2.135D)=" + dfScale2.format(2.135D)); System.out.println("dfScale2.format(2.145D)=" + dfScale2.format(2.145D)); System.out.println("dfScale2.format(2.225D)=" + dfScale2.format(2.225D)); System.out.println("dfScale2.format(2.235D)=" + dfScale2.format(2.235D)); System.out.println("dfScale2.format(2.245D)=" + dfScale2.format(2.245D)); System.out.println(); System.out.println("dfScale2.format(3.125D)=" + dfScale2.format(3.125D)); System.out.println("dfScale2.format(3.135D)=" + dfScale2.format(3.135D)); System.out.println("dfScale2.format(3.145D)=" + dfScale2.format(3.145D)); System.out.println("dfScale2.format(3.225D)=" + dfScale2.format(3.225D)); System.out.println("dfScale2.format(3.235D)=" + dfScale2.format(3.235D)); System.out.println("dfScale2.format(3.245D)=" + dfScale2.format(3.245D)); System.out.println(); System.out.println("dfScale2.format(4.125D)=" + dfScale2.format(4.125D)); System.out.println("dfScale2.format(4.135D)=" + dfScale2.format(4.135D)); System.out.println("dfScale2.format(4.145D)=" + dfScale2.format(4.145D)); System.out.println("dfScale2.format(4.225D)=" + dfScale2.format(4.225D)); System.out.println("dfScale2.format(4.235D)=" + dfScale2.format(4.235D)); System.out.println("dfScale2.format(4.245D)=" + dfScale2.format(4.245D)); } } |
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dfScale2.getRoundingMode()=HALF_EVENdfScale2.format(1.125D)=1.12dfScale2.format(1.135D)=1.14dfScale2.format(1.145D)=1.15dfScale2.format(1.225D)=1.23dfScale2.format(1.235D)=1.24dfScale2.format(1.245D)=1.25dfScale2.format(2.125D)=2.12dfScale2.format(2.135D)=2.13dfScale2.format(2.145D)=2.15dfScale2.format(2.225D)=2.23dfScale2.format(2.235D)=2.23dfScale2.format(2.245D)=2.25dfScale2.format(3.125D)=3.12dfScale2.format(3.135D)=3.13dfScale2.format(3.145D)=3.15dfScale2.format(3.225D)=3.23dfScale2.format(3.235D)=3.23dfScale2.format(3.245D)=3.25dfScale2.format(4.125D)=4.12dfScale2.format(4.135D)=4.13dfScale2.format(4.145D)=4.14dfScale2.format(4.225D)=4.22dfScale2.format(4.235D)=4.24dfScale2.format(4.245D)=4.25 |
正確的代碼測試RoundingMode.HALF_EVEN
突然發現自己忽略了一個事情,測試的參數都是用的double類型.想起來double類型不精準.但是僥幸心理以及知識不牢靠以為 3位小數應該影響不大吧.改了下代碼,把參數改為BigDecimal類型
使用BigDecimal時,參數盡量傳入字符串,要比傳入double精準.
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new BigDecimal("1.125") |
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@Testpublic void testDecimalFormat() { DecimalFormat dfScale2 = new DecimalFormat("###.##"); dfScale2.setRoundingMode(RoundingMode.HALF_EVEN); System.out.println("dfScale2.getRoundingMode()=" + dfScale2.getRoundingMode()); System.out.println("dfScale2.format(new BigDecimal(\"1.1251\"))=" + dfScale2.format(new BigDecimal("1.1251"))); System.out.println("dfScale2.format(new BigDecimal(\"1.1351\"))=" + dfScale2.format(new BigDecimal("1.1351"))); System.out.println("dfScale2.format(new BigDecimal(\"1.1451\"))=" + dfScale2.format(new BigDecimal("1.1451"))); System.out.println("dfScale2.format(new BigDecimal(\"1.2250\"))=" + dfScale2.format(new BigDecimal("1.2250"))); System.out.println("dfScale2.format(new BigDecimal(\"1.2350\"))=" + dfScale2.format(new BigDecimal("1.2350"))); System.out.println("dfScale2.format(new BigDecimal(\"1.2450\"))=" + dfScale2.format(new BigDecimal("1.2450"))); System.out.println("dfScale2.format(new BigDecimal(\"1.22501\"))=" + dfScale2.format(new BigDecimal("1.22501"))); System.out.println("dfScale2.format(new BigDecimal(\"1.23505\"))=" + dfScale2.format(new BigDecimal("1.23505"))); System.out.println("dfScale2.format(new BigDecimal(\"1.24508\"))=" + dfScale2.format(new BigDecimal("1.24508"))); |
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dfScale2.getRoundingMode()=HALF_EVENdfScale2.format(new BigDecimal("1.1251"))=1.13dfScale2.format(new BigDecimal("1.1351"))=1.14dfScale2.format(new BigDecimal("1.1451"))=1.15dfScale2.format(new BigDecimal("1.2250"))=1.22dfScale2.format(new BigDecimal("1.2350"))=1.24dfScale2.format(new BigDecimal("1.2450"))=1.24dfScale2.format(new BigDecimal("1.22501"))=1.23dfScale2.format(new BigDecimal("1.23505"))=1.24dfScale2.format(new BigDecimal("1.24508"))=1.25 |
結論
1、警覺doulbe的不精確所引起RoundingMode結果不穩定的問題,即使是四舍五入的模式,對double類型參數使用也會有不滿足預期的情況.
2、使用數字格式化時,要注意默認RoundingMode模式是否是自己需要的.如果不是記得手動設置下.
以上為個人經驗，希望能給大家一個參考，也希望大家多多支持服務器之家。
原文鏈接：https://blog.csdn.net/baixf/article/details/88792219
