Code Correctness: Comparison with NaN

Abstract

与 NaN 进行对比始终是一个错误。

Explanation

如果与 NaN 进行比较，得出的计算结果将始终为 false（!= 运算符是个例外，因为 NaN 未经排序，所以始终会得出 true 结果）。

示例 1：以下示例尝试验证变量并非为 NaN。


  ...
  if (result == Double.NaN){
    //something went wrong
    throw new RuntimeException("Something went wrong, NaN found");
  }
  ...

这将尝试验证 result 并非 NaN，但是使用带有 NaN 的运算符 == 将始终得出 false 值，所以此检查将永远不会抛出异常。

References

[1] NUM07-J. Do not attempt comparisons with NaN CERT

[2] Java Language Specification Chapter 4. Types, Values, and Variables Oracle

[3] INJECT-9: Prevent injection of exceptional floating point values Oracle

[4] Standards Mapping - Common Weakness Enumeration CWE ID 486

desc.structural.java.code_correctness_comparison_with_nan