"A generic sorting algorithm such as Quick Sort specifies how to sort elements, but it does not specify how those elements are ordered. Quick Sort needs to know when two elements, a and b, are in order, out of order, or equivalent so it can decide which partition each element belongs in. The elements could be numbers, strings, or user-defined objects. In Java, a Comparator object determines the proper order by implementing the method public int compare(T a, T b). A Comparator<T> is parameterized to operate on any type T, and the method takes two instances whose type matches T. The method returns a negative value if a comes before b, zero if a and b are equal, and a positive value if a comes after b. There is no guarantee about the magnitude of the returned value; it does not necessarily return -1 or +1."