Added Merge Sort Algorithm in Java

Program's_Contributed_By_Contributors/Java_Programs/Data_structure/MergeSort.java

@@ -0,0 +1,83 @@
+import java.util.Arrays;
+import java.util.Scanner;
+
+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 mergesort(int arr[], int l, int r)
+    {
+        if (l < r)
+        {
+            int m = (l+r)/2;
+
+            mergesort(arr, l, m);
+            mergesort(arr , m+1, r);
+
+            merge(arr, l, m, r);
+        }
+    }
+
+    public static void main(String args[])
+    {
+       Scanner sc = new Scanner(System.in);
+        System.out.println("Enter size of the array :");
+       int size = sc.nextInt();
+       int arr[] = new int[size];
+        System.out.println("Enter elements into the array: ");
+        for(int i= 0;i<size;i++){
+            arr[i] = sc.nextInt();
+        }
+        System.out.println("Array Before sorting : ");
+        System.out.println(Arrays.toString(arr));
+
+        MergeSort ob = new MergeSort();
+        ob.mergesort(arr, 0, arr.length-1);
+
+        System.out.println("Array After Sorting: ");
+        System.out.println(Arrays.toString(arr));
+    }
+}