Oddness check using `x % 2 == 1` will not work for negative numbersJAVA-E0405

The code uses an equivalent of x % 2 == 1 to check to see if a value is odd, but this won't work for negative numbers. If this code is intending to check for oddness, consider using x & 1 == 1, or x % 2 != 0.

Using a check like x % 2 == 1 will evaluate differently when x is negative than when x is positive:

 213 % 2  //  1

-213 % 2  // -1 !!!

 212 % 2  //  0

-212 % 2  //  0

Bad Practice

boolean badIsOdd(int x) {
    return x % 2 == 1;
}

assertTrue(BadIsOdd(-1)); // fails...

Recommended

Replace the equality check using 1 with an inequality check using 0 instead:

boolean goodIsOdd(int x) {
    return x % 2 != 0;
}

References

• SpotBugs - IM_BAD_CHECK_FOR_ODD