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According to \[[JLS Section 4.2.3, Floating-Point Types, Formats, and Values|http://java.sun.com/docs/books/jls/third_edition/html/typesValues.html#4.2.3]\]:

NaN is unordered, so the numerical comparison operators <, <=, >, and >= return false if either or both operands are NaN. The equality operator == returns false if either operand is NaN, and the inequality operator != returns true if either operand is NaN.

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Problems can ensue arise when the programmer uses such operators on NaN values in comparison operations. There is also a possibility that the input validation condition does not expect a NaN value as input.

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A frequently encountered mistake is the doomed comparison with NaN, typically in expressions. As per its semantics, no value (including NaN itself) can be compared to NaN using common operators, including NaN itself. This noncompliant example demonstrates one of such casesviolations.

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) // compare with infinity
      System.out.println("Both are equal");
  }
}

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Risk Assessment

Comparisons with NaN values may lead to unexpected results.

Automated Detection

TODO

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