Radix sort implementation in java

One of the basic sorting algorithms, named 'Radix Sort' implemented in java using Lists.

Time Complexity:
O(d*(n+b)) time where b is the base for representing numbers, for example, for decimal system, b is 10. What is the value of d? If k is the maximum possible value, then d would be O(logb(k)). So overall time complexity is O((n+b) * logb(k)).