我需要将一个浮点数舍入到Java中的两个小数位[重复]

Possible Duplicate:
How to round a number to n decimal places in Java

可能重复:如何在Java中将数字舍入到n个小数位

I am having difficulties rounding a float to two decimal places. I have tried a few methods I have seen on here including simply just using Math.round(), but no matter what I do I keep getting unusual numbers.

我很难将浮点数舍入到小数点后两位。我已经尝试了一些我在这里看到的方法,包括简单地使用Math.round(),但无论我做什么,我都会得到不寻常的数字。

I have a list of floats that I am processing, the first in the list is displayed as 1.2975118E7. What is the E7?

我有一个我正在处理的浮动列表,列表中的第一个显示为1.2975118E7。什么是E7?

When I use Math.round(f) (f is the float), I get the exact same number.

当我使用Math.round(f)(f是浮点数)时,我得到完全相同的数字。

I know I am doing something wrong, I just am not sure what.

我知道我做错了什么,我只是不确定是什么。

I just want the numbers to be in the format x.xx. The first number should be 1.30, etc.

我只想要数字格式为x.xx.第一个数字应该是1.30等

4 个解决方案

#1

1.2975118E7 is scientific notation.

1.2975118E7是科学记数法。

1.2975118E7 = 1.2975118 * 10^7 = 12975118

Also, Math.round(f) returns an integer. You can't use it to get your desired format x.xx.

此外,Math.round(f)返回一个整数。您不能使用它来获得所需的格式x.xx.

You could use String.format.

你可以使用String.format。

String s = String.format("%.2f", 1.2975118);
// 1.30

#2

If you're looking for currency formatting (which you didn't specify, but it seems that is what you're looking for) try the NumberFormat class. It's very simple:

如果您正在寻找货币格式(您没有指定,但似乎这是您正在寻找的),请尝试使用NumberFormat类。这很简单:

double d = 2.3d;
NumberFormat formatter = NumberFormat.getCurrencyInstance();
String output = formatter.format(d);

Which will output (depending on locale):

哪个将输出(取决于区域设置):

$2.30

Also, if currency isn't required (just the exact two decimal places) you can use this instead:

此外,如果不需要货币(只是精确的两位小数),您可以使用此代码:

NumberFormat formatter = NumberFormat.getNumberInstance();
formatter.setMinimumFractionDigits(2);
formatter.setMaximumFractionDigits(2);
String output = formatter.format(d);

Which will output 2.30

哪个会输出2.30

#3

You can make use of DecimalFormat to give you the style you wish.

您可以使用DecimalFormat为您提供所需的样式。

DecimalFormat df = new DecimalFormat("0.00E0");
double number = 1.2975118E7;
System.out.println(df.format(number));  // prints 1.30E7

Since it's in scientific notation, you won't be able to get the number any smaller than 10⁷ without losing that many orders of magnitude of accuracy.

由于它采用科学记数法,因此在不损失许多数量级精度的情况下,您将无法获得小于107的数字。

#4

-2

Try looking at the BigDecimal Class. It is the go to class for currency and support accurate rounding.

尝试查看BigDecimal类。这是货币的上课和支持准确的舍入。

#1