JAVA的HALF_DOWN和HALF_UP的区别?

Java代码:

public class BigDecimalDemo {
        public static void main(String[] args) {
                BigDecimal bd2=BigDecimal.valueOf(11);
                BigDecimal bd3=new BigDecimal("2.3");
                BigDecimal bdDiv = bd2.divide(bd3,38,RoundingMode.HALF_UP);
                System.out.println(bdDiv);
                BigDecimal bdDivDOWN = bd2.divide(bd3,10, RoundingMode.HALF_DOWN);
                System.out.println(bdDivDOWN);
                BigDecimal bdDivUP = bd2.divide(bd3,10, RoundingMode.HALF_UP);
                System.out.println(bdDivUP);
        }
}

  输出:

4.78260869565217391304347826086956521739
4.7826086957
4.7826086957

  题:
RoundingMode.HALF_DOWN和RoundingMode.HALF_UP的输出为何相同?

最佳答案

  好吧,RoundingMode.HALF_DOWN的javadoc说:

1、如果舍弃的分数> 0.5,则表现为RoundingMode.UP;否则,其行为与RoundingMode.DOWN相同。
RoundingMode.HALF_UP的Javadoc说:

2、如果舍弃分数≥0.5,则表现为RoundingMode.UP;否则,表现为RoundingMode.DOWN

在您的示例中,第二级和第三级中的废弃分数是0.5217391304347826086956521739,该分数> 0.5,因此两者的行为均RoundingMode.UP

仅当丢弃分数精确为0.5时,您才会看到不同的结果。

例如,以下内容:

BigDecimal bd2=BigDecimal.valueOf(11.12345678955);
BigDecimal bd3=new BigDecimal("1");
BigDecimal bdDiv = bd2.divide(bd3,38,RoundingMode.HALF_UP);
System.out.println(bdDiv);
BigDecimal bdDivDOWN = bd2.divide(bd3,10, RoundingMode.HALF_DOWN);
System.out.println(bdDivDOWN);
BigDecimal bdDivUP = bd2.divide(bd3,10, RoundingMode.HALF_UP);
System.out.println(bdDivUP);

将输出:

11.12345678955000000000000000000000000000
11.1234567895
11.1234567896

  

转自:java – Java中的HALF_DOWN和HALF_UP有什么区别? | RoundingMode (lmlphp.com)

 

原文地址:http://www.cnblogs.com/wwssgg/p/16852342.html

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