Can someone help me why this quick sort doesn't work

Question

public class QuickSortII {
     static void sort(int a[], int lo0, int hi0) {
        int lo = lo0;
        int hi = hi0;
        if (lo >= hi) {
            return;
        int mid = a[(lo + hi) / 2];
        while (lo < hi) {
            while (lo<hi && a[lo] < mid) {
                lo++;
            while (lo<hi && a[hi] >= mid) {
                hi--;
            if (lo < hi) {
                int T = a[lo];
                a[lo] = a[hi];
                a[hi] = T;
        if (hi < lo) {
            int T = hi;
            hi = lo;
            lo = T;
        sort(a, lo0, lo);
        sort(a, lo == lo0 ? lo+1 : lo, hi0);
    static void sort(int a[]) {
        sort(a, 0, a.length-1);
     static public void main(String[] args) {
          int a[] = new int[20];
          a[0] = 18;
          a[1] = 11;
          a[2] = 12;
          a[3] = 4;
          a[4] = 20;
          a[5] = 5;
          a[6] = 1;
          a[7] = 3;
          a[8] = 16;
          a[9] = 8;
          a[10] = 7;
          a[11] = 17;
          a[12] = 9;
          a[13] = 6;
          a[14] = 19;
          a[15] = 2;
          a[16] = 13;
          a[17] = 15;
          a[18] = 10;
          a[19] = 14;
          sort(a);
          for (int j = 0; j < 20; j++) {
               System.out.print(a[j] + " ");
}it doesn't sort the list

Answer 1

it doesn't sort the list Please explain why you think it should. Doing so will help you understand the code.
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