A Collection of Useful Classes - Beginning Java - page 691

is ascending, your compare() method establishes a descending sequence. If the surnames are equal, the
order is determined by the first names, again inverting the sign of the value returned by the compareTo()
method to maintain descending sequence. Of course, you could have coded this method by switching the
arguments, person1 and person2 , instead of reversing the sign:
public int compare(Person person1, Person person2) {
int result = person2.getSurname().compareTo(person1.getSurname());
return result == 0 ?
person2.getFirstName().compareTo(person1.getFirstName()) : result;
}
This would establish a descending sequence for Person objects.
You call the sort() method a second time with the statement:
Arrays.sort(authors); // Sort using
compareTo() method
Because you have not supplied a comparator, the sort() method expects the class type of the elements
to be sorted to have implemented the Comparable<> interface. Fortunately your Person class does, so
the authors get sorted. This time the result is in ascending sequence because that's what the compareTo()
method establishes.
Searching Arrays
The static binarySearch() method in the Arrays class searches the elements of a sorted array for a given
value using the binary search algorithm. This works only if the elements of the array are in ascending se-
quence, so if they are not, you should call the sort() method before calling binarySearch() . The binary
search algorithm works by repeatedly subdividing the sequence of elements to find the target element value,
as illustrated in Figure 15-1 .
FIGURE 15-1