BigDecimal乘法 [英] BigDecimal Multiplication

问题描述

我尝试将两个 BigDecimal 值乘以乘以方法，如下所示，

I try to multiply two BigDecimal Values with multiply methods as follows,

BigDecimal dur = BigDecimal.valueOf(60/1.1);
BigDecimal bal = BigDecimal.valueOf(1.1);

BigDecimal ans  = dur.multiply(bal);

System.out.println("Ans:"+ans);

我除了 60 。但我得到了它，

I am excepting ans as 60. But i got it as,

Ans:59.999999999999994

为什么会这样，我们如何解决呢。

Why this comming and how can we resolve it.

推荐答案

问题是你有一个不能在 double 中表示的值，但也不能在BigDecimal中表示，所以你必须应用合理的舍入来获得预期的解决方案。

The problem is you have a value which can't be represented in double but nor can it be represented in BigDecimal so you have to apply reasonable rounding to get the expected solution.

double d = 60 / 1.1 * 1.1;
System.out.println("double without rounding: " + d);
System.out.printf("double With rounding %.2f%n", d);

BigDecimal bd = BigDecimal.valueOf(60).divide(BigDecimal.valueOf(1.1), 9, BigDecimal.ROUND_HALF_UP).multiply(BigDecimal.valueOf(1.1));
System.out.println("BigDecimal without rounding: " + bd);
System.out.printf("BigDecimal with rounding %.2f%n", bd);
// or
bd = bd.setScale(2, BigDecimal.ROUND_HALF_UP);
System.out.println("BigDecimal with rounding: " + bd);

打印

double without rounding: 60.0
double With rounding 60.00
BigDecimal without rounding: 59.9999999995
BigDecimal with rounding 60.00
BigDecimal with rounding: 60.00

注意： double 恰好为这些值进行正确舍入并给出正确的答案。但是，选择一个不同的组合，它将是不正确的。例如 54.545454545454545 * 1.1 => 60.00000000000001

Note: double happens to round correctly for these values and gives the right answer. However, pick a different combination and it will be incorrect. e.g. 54.545454545454545 * 1.1 => 60.00000000000001

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