[GitHub] [poi] colinwjd commented on a diff in pull request #321: Fix rounding problems

[GitBox]

colinwjd commented on code in PR #321:
URL: https://github.com/apache/poi/pull/321#discussion_r845701701


##########
poi/src/main/java/org/apache/poi/ss/usermodel/DataFormatter.java:
##########
@@ -950,7 +950,7 @@ private String getFormattedNumberString(Cell cell, 
ConditionalFormattingEvaluato
         if (numberFormat == null) {
             return String.valueOf(d);
         }
-        String formatted = numberFormat.format(d);
+        String formatted = numberFormat.format(new 
BigDecimal(String.valueOf(d)));

Review Comment:
   <img width="190" alt="image" 
src="https://user-images.githubusercontent.com/7942918/162353067-28a23e52-9ff7-425b-93c2-891e2330ed69.png";>
   <img width="850" alt="image" 
src="https://user-images.githubusercontent.com/7942918/162353213-43151a9e-d10f-425d-a50b-2e46ed792071.png";>
   
   As shown above, the value 2.05 is correctly rounded to 2.1 in excel, but in 
the parsed result the value is 2.0 
   
   The reason is that the Double type has a loss of precision, so we need to 
use the BigDecimal type. 
   
   We need to use the String type to initialize the BigDecimal object, 
otherwise there will also be precision problems.
   It is described in the Java api documentation as follows
   > This is generally the preferred way to convert a float or double into a 
BigDecimal, as it doesn't suffer from the unpredictability of the 
BigDecimal(double) constructor.
   <img width="678" alt="image" 
src="https://user-images.githubusercontent.com/7942918/162354520-27fbc225-62c9-478b-a065-5cbbc97ad5d4.png";>
   



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