在 Java 中，什么时候浮点数等于零？
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In Java, when is a float equal to zero?
提问by Wilco
For what values of x does the test (x == 0) return true? Is there some kind of margin or does the test return true if and only if the value of x = 0?
对于 x 的哪些值，测试 (x == 0) 返回 true？是否存在某种边际，或者当且仅当 x = 0 时测试返回 true？
采纳答案by Wilco
A simple method can be written to find this value.
可以编写一个简单的方法来找到这个值。
public class FloatEqualsZero {
public static void main(String [] args) {
float x = 1;
while(x != 0 && -x != 0) {
x *= 0.1;
System.out.println(x);
}
}
}
This outputs the following:
这将输出以下内容：
0.1
0.01
9.999999E-4
9.999999E-5
9.999999E-6
9.999999E-7
...
1.0E-37
1.0E-38
1.0E-39
1.0E-40
1.0E-41
1.0E-42
1.0E-43
9.8E-45
1.4E-45
0.0
This (and similar tests) show that (x == 0) really only is true when x is 0.0f or -0.0f
这个（和类似的测试）表明 (x == 0) 只有当 x 为 0.0f 或 -0.0f 时才为真
回答by OldCurmudgeon
When it is equal to 0.0or -0.0.
当它等于0.0或 时-0.0。
public void test() {
double x = 0.0;
double y = -0.0;
double z = 0.0;
test(x, y);
test(y, z);
test(x, z);
test(x, (int)y);
test(y, (int)z);
test(x, (int)z);
}
private void test(double x, double y) {
System.out.println("x=" + x + " y=" + y + " \"x == y\" is " + (x == y ? "true" : "false"));
}
private void test(double x, int y) {
System.out.println("x=" + x + " y=" + y + " \"x == y\" is " + (x == y ? "true" : "false"));
}
prints
印刷
x=0.0 y=-0.0 "x == y" is true
x=-0.0 y=0.0 "x == y" is true
x=0.0 y=0.0 "x == y" is true
x=0.0 y=0 "x == y" is true
x=-0.0 y=0 "x == y" is true
x=0.0 y=0 "x == y" is true
回答by JonAar Livernois
When Math.signum(x)== 0.
当Math.signum(x)== 0。
All other attempts to check whether float x== 0 may fail.
所有其他尝试检查 float x== 0是否可能失败。
But Math.signum() is so basic, it should never fail.
但是 Math.signum() 非常基础，它永远不会失败。
