在Java中比较float和int是否安全？ [英] Is it safe to compare a float and an int in Java?

问题描述

  private static void foo（float n）{
 if（n> = 1 || n <= 0）{
 // code 
} 
} 
  

根据 JLS（5.6.2。Binary Numeric Promotion）如果其中一个参数是 float ，另一个是在比较之前转换为 float 。
但据我所知，这样的比较将返回true，如果转换的浮点数是二进制相同的原始浮点数。我们怎样才能保证它？

解决方案

是的，你的具体例子很好，因为 0 和 1 可以精确地表示为 float 。

请注意，这通常不是真的：有许多大的 int 值不能完全表示为 float 。例如，以下输出 true （ Ideone ）即使2_000_000_001不等于2_000_000_000：

$ p $ import java.util。*;
import java.lang。*;
import java.io. *;

class FloatTest {

private static boolean isTwoBillion（float f）{
return f == 2_000_000_000;


public static void main（String [] args）{
System.out.println（isTwoBillion（2_000_000_001））;


$ b $ / code $ / pre



请注意，与 float ， double 具有足够的尾数来存储每个32位 int 价值。

Is it safe to compare a float and an integer like this?

private static void foo(float n) {
    if (n >= 1 || n <= 0) {
      // code 
    } 
}

According to the JLS (5.6.2. Binary Numeric Promotion) if one of the parameters is float, the other is converted to float before comparison. But as far as I understand, such a comparison will return true if the converted float is binary identical to the original float. How can we ensure it?

解决方案

Yes, your specific example is fine, since both 0 and 1 can be exactly represented as a float.

Note that this is not true in general: there are many large int values that's can't be represented exactly as a float. For example, the following prints out true (Ideone) even though 2_000_000_001 does not equal 2_000_000_000:

import java.util.*;
import java.lang.*;
import java.io.*;

class FloatTest {

    private static boolean isTwoBillion(float f) {
        return f == 2_000_000_000;
    }

    public static void main (String[] args) {
        System.out.println(isTwoBillion(2_000_000_001));
    }

}

Note that, unlike float, double has wide enough mantissa to store every 32-bit int value.

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