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This noncompliant code example attempts a direct comparison with NaN. In accordance with the semantics of NaN, all comparisons with NaN yield false (with the exception of the != operator, which returns true). Consequently, this comparison always return false, and the "result is NaN" message is never printed.
| Code Block | ||
|---|---|---|
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public class NaNComparison {
public static void main(String[] args) {
double x = 0.0;
double result = Math.cos(1/x); // returns NaN if input is infinity
if (result == Double.NaN) { // comparison is always false!
System.out.println("result is NaN");
}
}
}
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This compliant solution uses the method Double.isNaN() to check whether the expression corresponds to a NaN value.
| Code Block | ||
|---|---|---|
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public class NaNComparison {
public static void main(String[] args) {
double x = 0.0;
double result = Math.cos(1/x); // returns NaN when input is infinity
if (Double.isNaN(result)) {
System.out.println("result is NaN");
}
}
}
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FE: Doomed test for equality to NaN | |
[JLS 2005] | |
| [Seacord 2015] |
NUM06-J. Use the strictfp modifier for floating-point calculation consistency across platforms