Minor Description
The hashCode() methods of the range classes look very suspicious to me. The value is lazily initialized, but the calculation is done _on the cached value. With some unlucky timing a caller may get an incomplete hash.
An unlucky sequence of Code could be something like
T1: if (hashCode == 0) // true
T1: hashCode = 17;
T2: if (hashCode == 0) // now false because hashCode was already set to 17
T2: return hashCode; // return 17
T1: hashCode = 37 * hashCode...........
where T1 and T2 are different threads accessing the method in parallel and T2 gets the wrong hash "17".
Affected classes are
org.apache.commons.lang.math.DoubleRange
org.apache.commons.lang.math.FloatRange
org.apache.commons.lang.math.IntRange
org.apache.commons.lang.math.LongRange
org.apache.commons.lang.math.NumberRange
org.apache.commons.lang.math.Range
Possible fix: calculate the hash on a temporary variable and finally assign it to the member