Java float 123.129456到123.12没有舍入 [英] Java float 123.129456 to 123.12 without rounding

问题描述

如何将java中的 float 原语减少到两个十进制的位置，而不使用舍入？

  123.99999 to 123.99 
 -8.022222 to -8.02 
  

不应该舍入小数位，而是留下两位。第二点是如何验证或计算点后的小数点数：
$ b $ b

  123.99会给出true或2 
 123.999会给出false或3 
  

---

UPDATE

这些数字是字符串输入，所以我想我会一起去建议;我只是有int try / catch块的例外。任何建议如何让这个工作更聪明的方式是欢迎：

pre $ 公共静态浮动onlyTwoDecimalPlaces（字符串数字）{
StringBuilder sbFloat = new StringBuilder（number）;
int start = sbFloat.indexOf（。）;
if（start <0）{
return new Float（sbFloat.toString（））;
}
int end = start + 3; （（end）>（sbFloat.length（） - 1））end = sbFloat.length（）;

String twoPlaces = sbFloat.substring（start，end）;
sbFloat.replace（start，sbFloat.length（），twoPlaces）;
返回新的浮点数（sbFloat.toString（））;



解决方案

首先，不能保证只是因为一个float可以精确地表示 a.bcde ，它可以保证能够表示 a.bc

所以如果你只是在打印部分之后，那么用一些字符串操作呢？使用 indexOf 查找小数点，并使用 substring 。 b

How do you cut down float primitive in java to two decimal places, without using rounding?:

123.99999 to 123.99
-8.022222 to -8.02

There should be no rounding just cut of the decimal places and leave two.

Second point is how do you validate or count how many decimals are after the point?:

123.99 will give true or 2
123.999 will give false or 3

---

UPDATE

The numbers are String input so I think I will go with this as suggested; and I'll just have int try/catch block for any exceptions. Any suggestions how to make this work any smarter way are welcome:

public static float onlyTwoDecimalPlaces(String number) {
    StringBuilder sbFloat = new StringBuilder(number);
    int start = sbFloat.indexOf(".");
    if (start < 0) {
        return new Float(sbFloat.toString());
    }
    int end = start+3;
    if((end)>(sbFloat.length()-1)) end = sbFloat.length();

    String twoPlaces = sbFloat.substring(start, end);
    sbFloat.replace(start, sbFloat.length(), twoPlaces);
    return new Float(sbFloat.toString());
}

解决方案

First of all, there is no guarantee that just because a float can represent a.bcde exactly, it is guaranteed to be able to represent a.bc exactly.

So if you're after just the printing part, how about doing it with some string-manipulation? Find the decimal point using indexOf and extract the part with two decimals, using substring.

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