如何检查0是正的还是负的?

Is it possible to check if a float is a positive zero (0.0) or a negative zero (-0.0)?

是否可以检查一个浮点数是正值(0.0)还是负值(-0.0)?

I've converted the float to a String and checked if the first char is a '-', but are there any other ways?

我已经将浮点数转换为字符串，并检查第一个字符是否是“-”，但是还有其他方法吗?

7 个解决方案

#1

Yes, divide by it. 1 / +0.0f is +Infinity, but 1 / -0.0f is -Infinity. It's easy to find out which one it is with a simple comparison, so you get:

是的,除以它。1 / +0。0f = +∞，但1 / -0。0f = -∞。通过简单的比较，很容易找出是哪一个，所以你得到:

if (1 / x > 0)
    // +0 here
else
    // -0 here

(this assumes that x can only be one of the two zeroes)

(假设x只能是两个0中的一个)

#2

You can use Float.floatToIntBits to convert it to an int and look at the bit pattern:

您可以使用浮动。floatToIntBits转换为int并查看位模式:

float f = -0.0f;

if (Float.floatToIntBits(f) == 0x80000000) {
    System.out.println("Negative zero");
}

#3

Definitly not the best aproach. Checkout the function

肯定不是最好的。付款功能

Float.floatToRawIntBits(f);

Doku:

多库:

/**
 * Returns a representation of the specified floating-point value
 * according to the IEEE 754 floating-point "single format" bit
 * layout, preserving Not-a-Number (NaN) values.
 *
 * <p>Bit 31 (the bit that is selected by the mask
 * {@code 0x80000000}) represents the sign of the floating-point
 * number.
 ...
 public static native int floatToRawIntBits(float value);

#4

The approach used by Math.min is similar to what Jesper proposes but a little clearer:

数学使用的方法。min类似于Jesper的提议，但更清楚一点:

private static int negativeZeroFloatBits = Float.floatToRawIntBits(-0.0f);

float f = -0.0f;
boolean isNegativeZero = (Float.floatToRawIntBits(f) == negativeZeroFloatBits);

#5

Double.equals distinguishes ±0.0 in Java. (There's also Float.equals.)

翻倍。在Java =区分±0.0。(还有Float.equals。)

I'm a bit surprised no-one has mentioned these, as they seem to me clearer than any method given so far!

我有点惊讶没有人提到这些，因为它们在我看来比迄今为止给出的任何方法都要清楚!

#6

When a float is negative (including -0.0 and -inf), it uses the same sign bit as a negative int. This means you can compare the integer representation to 0, eliminating the need to know or compute the integer representation of -0.0:

当一个浮点数为负(包括-0.0和-inf)时，它使用的符号位与负int相同。

if(f == 0.0) {
  if(Float.floatToIntBits(f) < 0) {
    //negative zero
  } else {
    //positive zero
  }
}

That has an extra branch over the accepted answer, but I think it's more readable without a hex constant.

这在被接受的答案上有一个额外的分支，但是我认为没有十六进制常数更容易阅读。

If your goal is just to treat -0 as a negative number, you could leave out the outer if statement:

如果你的目标是把-0看成一个负数，那么你可以省略If语句:

if(Float.floatToIntBits(f) < 0) {
  //any negative float, including -0.0 and -inf
} else {
  //any non-negative float, including +0.0, +inf, and NaN
}

#7

For negative:

负面:

new Double(-0.0).equals(new Double(value));

For positive:

积极的:

new Double(0.0).equals(new Double(value));

#1