java程式碼：

 1 public static void main(String[] args) {
 2         int arr[] = {2,7,1,5,9,6,10}; //要排序的陣列
 3         int temp[] = new int[arr.length]; //中間陣列
 4         mergeSort(arr,0,arr.length-1,temp);
 5         System.out.println(Arrays.toString(arr));
 6     }
 7 
 8     //分解加合併方法，即歸併排序
 9     public static
 
 void mergeSort(int arr[], int left,int right, int temp[]) {
10         if (left >= right) {
11             return;
12         }
13         if (left < right) {
14             int mid = (left + right)/2; //以中間索引進行分解
15             //分離左邊序列
16             mergeSort(arr, left, mid, temp);
17             //
 
分離右邊序列
18             mergeSort(arr, mid+1, right, temp);
19             //合併
20             merge(arr, left, mid, right, temp);
21         }
22     }
23 
24     //合併
25     public static void merge(int arr[], int left, int mid, int right, int temp[]) {
26         int i = left;//左邊有序序列初始索引
27         int j = mid+1
 
;//右邊有序序列初始索引
28         int t = 0; //temp 初始索引
29 
30         //先把左右兩邊有序的資料按規則填充到temp陣列中
31         //直到左右兩邊有序序列有一邊不能處理為止
32         while ( i<=mid && j<=right) {
33             //比較左邊和右邊的資料，小的那方先存入temp
34             if ( arr[i] <= arr[j]) {
35                 temp[t] = arr[i];
36                 t += 1;
37                 i += 1;
38             } else {
39                 temp[t] = arr[j];
40                 t += 1;
41                 j += 1;
42             }
43         }
44         //如果有一邊有剩餘資料則依次填入temp陣列中
45         while ( i<=mid){
46             temp[t] = arr[i];
47             t += 1;
48             i += 1;
49         }
50         while ( j<=right ) {
51             temp[t] = arr[j];
52             t += 1;
53             j += 1;
54         }
55         //將temp陣列拷貝到arr中
56         //並不是一次性合併完後拷貝進陣列
57         t = 0;
58         int tempLeft = left; //左邊要合併序列的索引
59         System.out.println("tl="+tempLeft + "right"+right);
60         while(tempLeft<=right) {
61             arr[tempLeft] = temp[t];
62             t += 1;
63             tempLeft += 1;
64         }
65 }

多執行緒版本：

 1  public static void main (String[] args) throws InterruptedException {
 2         int[] arr = {2,7,1,5,9,6,10,50,20,30,66,11,45,111};
 3         printArr(arr);
 4         System.out.println();
 5         int[] temp = new int[arr.length];
 6         //Fork/Join 從這裡開始
 7         ForkJoinPool forkJoinPool = new ForkJoinPool();
 8         ll.mergeTask task = new ll.mergeTask(arr, temp, 0, arr.length-1);//建立任務
 9         forkJoinPool.execute(task);//執行任務
10         forkJoinPool.awaitTermination(2, TimeUnit.SECONDS);//阻塞當前執行緒直到pool中的任務都完成了
11 
12         printArr(arr);
13         System.out.println();
14     }
15 
16     //遞迴
17     private static void mergeSort(int[] nums,int[] tmp,int left,int right){
18         if(left<right){
19             int center = (left+right)/2;
20             mergeSort(nums,tmp,left,center);
21             mergeSort(nums,tmp,center+1,right);
22             merge(nums,tmp,left,center+1,right);
23         }
24     }
25 
26     //合併
27     private static void merge(int[] nums,int[] tmp,int leftPos, int rightPos, int rightEnd){
28         int leftEnd = rightPos-1;
29         int tmpPos = leftPos;
30         int numElements = rightEnd - leftPos + 1;
31 
32         while(leftPos<=leftEnd&&rightPos<=rightEnd){
33             if(nums[leftPos]<nums[rightPos])
34                 tmp[tmpPos++]=nums[leftPos++];
35             else
36                 tmp[tmpPos++]=nums[rightPos++];
37         }
38         while(leftPos<=leftEnd)
39             tmp[tmpPos++]=nums[leftPos++];
40 
41         while(rightPos<=rightEnd)
42             tmp[tmpPos++]=nums[rightPos++];
43 
44         for(int i = 0;i<numElements;i++,rightEnd--)
45             nums[rightEnd]=tmp[rightEnd];
46     }
47     public static void mergeSort(int[] nums){
48         int[] tmp = new int[nums.length];
49         mergeSort(nums,tmp,0,nums.length-1);
50     }
51 
52     //列印
53     public static void printArr(int[] arr) {
54         for(int i : arr){
55             System.out.print(i+" ");
56         }
57     }
58 
59     static class mergeTask extends RecursiveAction {
60         private static final int THRESHOLD = 2;//設定任務大小閾值
61         private int start;
62         private int end;
63         private int[] data;
64         private int[] tmp;
65 
66         public mergeTask(int[] data, int[] tmp, int start, int end){
67             this.data = data;
68             this.tmp = tmp;
69             this.start = start;
70             this.end = end;
71         }
72 
73         @Override
74         protected void compute(){
75             if((end - start)<=THRESHOLD){
76                 mergeSort(data,tmp,start,end);
77             }else{
78                 int center = (start + end)/2;
79                 ll.mergeTask leftTask = new ll.mergeTask(data, tmp, start, center);
80                 ll.mergeTask rightTask = new ll.mergeTask(data, tmp, center+1, end);
81 
82                 leftTask.fork();
83                 rightTask.fork();
84 
85                 leftTask.join();
86                 rightTask.join();
87 
88                 merge(data, tmp, start, center+1, end);
89 
90             }
91         }
92     }