我发现了这个快速排序的代码实现，我想问：代码中粗体部分是做什么的？是检查数组的左右部分是否有未排序的元素吗？

import java.util.Scanner;

public class QuickSort {
    static int a[];

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.print("n = ");
        int n = sc.nextInt();

        System.out.println("Array: ");
        a = new int[n];

        for (int i = 0; i < n; i++) {
            a[i] = sc.nextInt();
        }

        quickSort(0, n - 1);

        System.out.println("Sorted array: ");
        for (int i = 0; i < n; i++) {
            System.out.print(a[i] + " ");
        }

        sc.close();

    }

    private static void quickSort(int left, int right) {
        int i = left, j = right;

        int pivot = a[(left + right) / 2];

        while (i <= j) {
            while (a[i] < pivot) {
                i++;
            }

            while (a[j] > pivot) {
                j--;
            }

            if (i <= j) {
                swap(a, i, j);
                i++;
                j--;
            }
        }

        if (left < j) {
            quickSort(left, j);
        }

        if (i < right) {
            quickSort(i, right);
        }
    }

    private static void swap(int a[], int index1, int index2) {
        int aux = a[index1];
        a[index1] = a[index2];
        a[index2] = aux;
    }
}

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我试着理解代码在做什么。