为随机数组添加合并排序方法

Question

我制作了一些生成随机数组的代码并通过快速排序。但是，我需要对合并排序算法做同样的事情，但我不确定如何。我也确保有一个菜单，以便可以隔离一个阵列。任何人都可以发布一些关于如何添加合并排序方法的想法吗？

  import java.util.Scanner;
  import java.util.Random;
  public class Algo {

  public static void main(String[] args) {
  Random gen = new Random();
  Scanner scanner = new Scanner(System.in);
  int[] a = new int[20];

  for (int i = 0; i < a.length; i++)
    a[i] = gen.nextInt(100);

  System.out.println("1. Quick Sort");
  System.out.println("2. Merge Sort");
  System.out.println("what number do you want?");
  int choice = scanner.nextInt();
  if (choice == 1) {
  System.out.println("Quick sort:");
  printArray(a);
  quickSort(a, 0, a.length - 1);
  printArray(a);
  }
  else 
  {
  System.out.println("Merge sort:");
  printArray(a);
  //MERGE SORT NEEDED
  printArray(a);
  }


}

 private static void printArray(int[] a){
  for (int i : a)
    System.out.print(i + " ");
  System.out.println("");
}
private static void quickSort(int a[], int left, int right)
{
  int i = left, j = right;
  int tmp;
  int pivot = a[(left + right) / 2];
  while (i <= j) {
        while (a[i] < pivot)
              i++;
        while (a[j] > pivot)
              j--;
        if (i <= j) {
              tmp = a[i];
              a[i] = a[j];
              a[j] = tmp;
              i++;
              j--;
    }
}
if (left < j)
    quickSort(a, left, j);
if (i < right)
        quickSort(a, i, right);
}
private static void printArrays(int[] a, int tmp){
System.out.println();
for (int x = 0; x < a.length; x++){
System.out.print(tmp);
}
}
}