Added MergeSort Implementation in Java (#28042)

* Added MergeSort Implementation in Java

* fix: changed c++ to cpp

guide/english/algorithms/sorting-algorithms/merge-sort/index.md

@@ -455,6 +455,79 @@ end
 
 ```
 
+### Implementation in Java
+```Java
+class MergeSort 
+{
+    void merge(int arr[], int l, int m, int r) 
+    {
+        int n1 = m - l + 1; 
+        int n2 = r - m; 
+        int L[] = new int [n1]; 
+        int R[] = new int [n2];
+        for (int i=0; i<n1; ++i) 
+            L[i] = arr[l + i]; 
+        for (int j=0; j<n2; ++j) 
+            R[j] = arr[m + 1+ j]; 
+        int i = 0, j = 0; 
+        int k = l; 
+        while (i < n1 && j < n2) 
+        { 
+            if (L[i] <= R[j]) 
+            { 
+                arr[k] = L[i]; 
+                i++; 
+            } 
+            else
+            { 
+                arr[k] = R[j]; 
+                j++; 
+            } 
+            k++; 
+        } 
+        while (i < n1) 
+        { 
+            arr[k] = L[i]; 
+            i++; 
+            k++; 
+        } 
+        while (j < n2) 
+        { 
+            arr[k] = R[j]; 
+            j++; 
+            k++; 
+        } 
+    } 
+    void sort(int arr[], int l, int r) 
+    { 
+        if (l < r) 
+        {
+            int m = (l+r)/2;
+            sort(arr, l, m); 
+            sort(arr , m+1, r); 
+            merge(arr, l, m, r); 
+        } 
+    } 
+    static void printArray(int arr[]) 
+    { 
+        int n = arr.length; 
+        for (int i=0; i<n; ++i) 
+            System.out.print(arr[i] + " "); 
+        System.out.println(); 
+    }
+    public static void main(String args[]) 
+    { 
+        int arr[] = {12, 11, 13, 5, 6, 7}; 
+        System.out.println("Given Array"); 
+        printArray(arr); 
+        MergeSort ob = new MergeSort(); 
+        ob.sort(arr, 0, arr.length-1);
+        System.out.println("\n The Sorted array is : "); 
+        printArray(arr); 
+    } 
+}
+```
+
 ### Relavant videos on freeCodeCamp YouTube channel
 * <a href='https://youtu.be/TzeBrDU-JaY'>Merge Sort algorithm - MyCodeSchool</a>