MathAbsoluteNegative
Math.abs() does not always give a non-negative result. Please consider other methods for positive numbers, such as IntMath.saturatedAbs() or Math.floorMod().

Alternate names: MathAbsoluteRandom

The problem

Math.abs returns a negative number when called with the largest negative number.

Example:

int veryNegative = Math.abs(Integer.MIN_VALUE); long veryNegativeLong = Math.abs(Long.MIN_VALUE); 

When trying to generate positive random numbers or fingerprints by using Math.abs around a random positive-or-negative integer (or long), there will a rare edge case where the returned value will be negative.

This is because there is no positive integer with the same magnitude as Integer.MIN_VALUE, which is equal to -Integer.MAX_VALUE - 1. Floating point numbers don’t suffer from this problem, as the sign is stored in a separate bit.

Instead, one should use random number generation functions that are guaranteed to generate positive numbers:

Random r = new Random(); int positiveNumber = r.nextInt(Integer.MAX_VALUE); 

or map negative numbers onto the non-negative range:

long lng = r.nextLong(); long bestForHashCodes = lng & Long.MAX_VALUE; long bestForMath = LongMath.saturatedAbs(lng); 

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("MathAbsoluteNegative") to the enclosing element.