Sort a given string in ascending order

Question

This code sort the string below in ascending order.

I'd prefer it split-up in two or three smaller, simpler methods. I'm also wondering whether my algorithm has a decent time complexity.

Given string

[H, B, D, G, F, E, A, C]

Output

[A, B, C, D, E, F, G, H]

public class sortArray {
 public static void sort (String[] str)
 {
 int lastPos = str.length - 1;
 int minPos = 0;
 String s = "";
 for (int i = 0; i < lastPos; i++)
 {
 minPos = i;
 for (int j = i + 1; j <= lastPos; j++)
 if (str[j].compareTo (str[minPos]) < 0)
 minPos = j;
 if (minPos != i)
 {
 s = str[i];
 str[i] = str[minPos];
 str[minPos] = s;
 }
 }
 }
 public static void main(String[] args){
 String[] str = {"H", "B", "D", "G","F", "E", "A", "C"};
 sort(str);
 System.out.println(Arrays.toString(str));
 }
}

• Jude Niroshan: In case if you are trying to sort an array, you could have achieve this whole thing with Arrays.sort(str);

Answer 1

Your algorithm is selection sort.

Selection sort has a time complexity of \$O(n^2)\$. For sorting algorithms, that's pretty slow.

Consider looking up a sorting algorithm such as quicksort, which, whilst it does have a worst case performance of \$O(n^2)\,ドル on average, it tends to take \$O(n log n)\$.

Or, as suggested in the comments, make use of the built-in libraries. Use Arrays.sort. Use of library code, especially when part of the language that you're programming in, can save significantly on the work you need to do.

---

Splitting up your code into several methods can be done.

Take this section, for instance.

 for (int j = i + 1; j <= lastPos; j++)
 if (str[j].compareTo (str[minPos]) < 0)
 minPos = j;

What it does is it looks for the smallest string in the array. So you could turn this into a function, with arguments for the array and the starting position (array.length will get you the end).

The swap,

 if (minPos != i)
 {
 s = str[i];
 str[i] = str[minPos];
 str[minPos] = s;
 }

Could also be a separate method.

If you extract those two sections of code to separate functions, the main sorting function will look like this:

public static void sort (String[] str)
{
 int lastPos = str.length - 1;
 for (int i = 0; i < lastPos; i++)
 {
 swap(str, i, findSmallest(str, i));
 }
}