Java: "Double.isNaN" or "Float.isNaN" should be used

When working with float or double primitive types, it may be required to deal with NaN (Not a Number) values. When tested against itself, NaN will always answer false as long as the primitive wrapper type is not used. When the wrapper is used, it will always be true. This property is illustrated in the code snipped below.

double d = getValue();
if (d == d) { // false for primitive 'double' when NaN, and true for any non-NaN values
  doSomething();
}

Double bigD = getValue();
if (bigD == bigD) { // always true for wrapper type 'Double' when NaN, AND with any other Double value
  doSomething(); 
}

In order to remove any ambiguity, this rule raises an issue every time an equality test is used with double, Double, float or Float, when both sides of the test are the same variable. The isNaN(...) methods from Double and Float should be preferred.

Noncompliant Code Example

double x = getValue();
if (x == x) { // Noncompliant
  doSomething();
}
if (x == Double.NaN) { // Noncompliant
  doSomething();
}

Compliant Solution

double x = getValue();
if (Double.isNaN(x)) { // compliant
  doSomething();
}