# Java Program to Implement Merge Sort Algorithm

## Example: Java Program to Implement Merge Sort Algorithm

``````
import java.util.Arrays;

// Merge sort in Java

class Main{

// Merge two sub arrays L and M into array
void merge(int array[], int p, int q, int r){

int n1 = q - p + 1;
int n2 = r - q;

int L[] = new int[n1];
int M[] = new int[n2];

// fill the left and right array
for (int i = 0; i < n1; i++)
L[i] = array[p + i];
for (int j = 0; j < n2; j++)
M[j] = array[q + 1 + j];

// Maintain current index of sub-arrays and main array
int i, j, k;
i = 0;
j = 0;
k = p;

// Until we reach either end of either L or M, pick larger among
// elements L and M and place them in the correct position at A[p..r]
// for sorting in descending
// use if(L[i] >= <[j])
while (i < n1 && j < n2) {
if (L[i] <= M[j]) {
array[k] = L[i];
i++;
} else {
array[k] = M[j];
j++;
}
k++;
}

// When we run out of elements in either L or M,
// pick up the remaining elements and put in A[p..r]
while (i < n1) {
array[k] = L[i];
i++;
k++;
}

while (j < n2) {
array[k] = M[j];
j++;
k++;
}
}

// Divide the array into two sub arrays, sort them and merge them
void mergeSort(int array[], int left, int right){
if (left < right) {

// m is the point where the array is divided into two sub arrays
int mid = (left + right) / 2;

// recursive call to each sub arrays
mergeSort(array, left, mid);
mergeSort(array, mid + 1, right);

// Merge the sorted sub arrays
merge(array, left, mid, right);
}
}

public static void main(String args[]){

// created an unsorted array
int[] array = { 6, 5, 12, 10, 9, 1 };

Main ob = new Main();

// call the method mergeSort()
// pass argument: array, first index and last index
ob.mergeSort(array, 0, array.length - 1);

System.out.println("Sorted Array:");
System.out.println(Arrays.toString(array));
}
}
``````

Output 1

```Unsorted Array:
[6, 5, 12, 10, 9, 1]
Sorted Array:
[1, 5, 6, 9, 10, 12]```

Here, the elements of the array are sorted in ascending order. If we want to sort the elements in descending order, then inside the first `while` loop of the `merge()` method, we can change the code as:

``````// the less than sign is changed to greater than
if (L[i] >= M[j]) {``````

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`Disclaimer: The information and code presented within this recipe/tutorial is only for educational and coaching purposes for beginners and developers. Anyone can practice and apply the recipe/tutorial presented here, but the reader is taking full responsibility for his/her actions. The author (content curator) of this recipe (code / program) has made every effort to ensure the accuracy of the information was correct at time of publication. The author (content curator) does not assume and hereby disclaims any liability to any party for any loss, damage, or disruption caused by errors or omissions, whether such errors or omissions result from accident, negligence, or any other cause. The information presented here could also be found in public knowledge domains.  `