returns a negative number when called with the largest negative number.
int veryNegative = Math.abs(Integer.MIN_VALUE); long veryNegativeLong = Math.abs(Long.MIN_VALUE);
When trying to generate positive random numbers 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(); lng = (lng == Long.MIN_VALUE) ? 0 : Math.abs(lng);
Suppress false positives by adding the suppression annotation
@SuppressWarnings("MathAbsoluteRandom") to the enclosing element.