Quicksort using generics in java

Question

The goal is to have a function that can sort a series of all object types that implement the comparable interface. I'm not trying to improve the performance of the sort. I'm only trying to optimize my use of generics.

I currently use T extends whatever and T[], however I was also considering to use T extends whatever and ArrayList<T>. Is one more preferable over the other or are both approaches just trash? If you have other remarks please tell me I'm here to learn :)

 public static void main( String[] args )
 {
 String[] stringList = {"hello", "this", "is", "a", "test", "ab", "aaa","aba"};
 
 Quicksort.sort(stringList, 0, stringList.length - 1);
 System.out.println( Arrays.toString(stringList));
 }

public class Quicksort{
 private static <T extends Comparable<T>> int partitioning(T[] arr, int start, int end) {
 T pivot = arr[end];
 int balancePoint = start; // everything that's smaller to the left of this, the rest to the right
 for (int i = start; i < end; i++) {
 if(arr[i].compareTo(pivot)<=0) {
 Arrayswap.genericArraySwap(arr, i, balancePoint);
 balancePoint++;
 }
 }
 Arrayswap.genericArraySwap(arr, end, balancePoint);
 return balancePoint;
 }
 public static <T extends Comparable<T>> void sort(T[]a, int i, int j) {
 if (i>=j) {
 return;
 }
 int pivot = partitioning(a, i, j);
 sort(a, i, pivot-1);
 sort(a, pivot+1, j);
 }
}

• Maarten Bodewes: Er, there is a space too many after main( and before the closing ) - not consistent ;)

Answer 1

Welcome to Code Review, the use of <T extends Comparable<T>> and T[] looks fine to me and personally I would not change it. The only one thing I am not agree is about the indexes you use to order one array like below :

Quicksort.sort(stringList, 0, stringList.length - 1);

In the java sorting methods from the std library the range to be sorted extends from the starting index, inclusive, to the end index, exclusive, so for me your method should be rewritten in the way that ordering an array arr of length n should be obtained by Quicksort.sort(arr, 0, n).

• BugSquanch: Hi Thanks for your feedback. Making the last parameter inclusive is indeed more consistent. Thanks again for your time :)
• dariosicily: @DevShot You are welcome and again good job :)