Added java implementation of merge sort (#23993)

* Added java implementation of merge sort

* fix: changed to two space indentation

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

@@ -306,3 +306,54 @@ public class mergesort {
 }
 
 ```
+### Example in Java
+```java
+public class mergesort {
+  public static int[] mergesort(int[] arr, int lo, int hi) {
+    if (lo == hi) {
+      int[] ba = new int[1];
+      ba[0] = arr[lo];
+      return ba;
+    }
+    int mid = (lo + hi) / 2;
+    int arr1[] = mergesort(arr, lo, mid);
+    int arr2[] = mergesort(arr, mid + 1, hi);
+    return merge(arr1, arr2);
+  }
+
+  public static int[] merge(int[] arr1, int[] arr2) {
+    int i = 0, j = 0, k = 0;
+    int n = arr1.length;
+    int m = arr2.length;
+    int[] arr3 = new int[m + n];
+    while (i < n && j < m) {
+      if (arr1[i] < arr2[j]) {
+        arr3[k] = arr1[i];
+        i++;
+      } else {
+        arr3[k] = arr2[j];
+        j++;
+      }
+      k++;
+    }
+    while (i < n) {
+      arr3[k] = arr1[i];
+      i++;
+      k++;
+    }
+    while (j < m) {
+      arr3[k] = arr2[j];
+      j++;
+      k++;
+    }
+    return arr3;
+  }
+
+  public static void main(String[] args) {
+    int arr[] = {2, 9, 8, 3, 6, 4, 10, 7};
+    int[] so = mergesort(arr, 0, arr.length - 1);
+    for (int i = 0; i < arr.length; i++)
+      System.out.print(so[i] + " ");
+  }
+}
+```