BigDecimal刻度不起作用

问题描述

我有以下代码:

BigDecimal result = BigDecimal.ZERO;
result.setScale(2, BigDecimal.ROUND_FLOOR); //1
BigDecimal amountSum;

// amount sum computation

BigDecimal amountByCurrency = amountSum.divide(32); //-0.04
result.add(amountByCurrency); //2

//1行之后的小数位数仍为0.为什么?因此，//2评估不会影响结果.怎么了?

After line //1 scale is still 0. Why? So, the //2 evaluation doesn't affect to the result. What's wrong?

推荐答案

是这样的:

The important part of the #setScale documentation is this:

(添加了重点)

因此，代码中的这一行不会更改result实例:

Therefore, this line in your code won't change the result instance:

result.setScale(2, BigDecimal.ROUND_FLOOR); //1

将其更改为:

result = result.setScale(2, BigDecimal.ROUND_FLOOR);

用新实例覆盖实例，或创建一个新变量并使用它代替result:

to overwrite the instance with the new one, or create a new variable and use that instead of result:

BigDecimal scaledResult = result.setScale(2, BigDecimal.ROUND_FLOOR);

顺便说一句:这条线也一样:

Btw: the same applies to this line:

result.add(amountByCurrency); //2

您需要将返回的#add调用的BigDecimal实例存储在变量中.

You need to store the returned BigDecimal instance of the #add call in a variable.

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