added merge sort algorithms using java

Sorting Algorithms/Merge_sort (java alg).java

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+/*
+ * To change this license header, choose License Headers in Project Properties.
+ * To change this template file, choose Tools | Templates
+ * and open the template in the editor.
+ */
+package merge_sort;
+
+import java.util.Arrays;
+
+/**
+ *
+ * @author Bhashitha
+ */
+public class Merge_sort {
+
+    /**
+     * @param args the command line arguments
+     */
+     public static void main(String[] args)
+    {
+        //Unsorted array
+        Integer[] a = { 2, 6, 3, 5, 1 };
+
+        //Call merge sort
+        mergeSort(a);
+
+        //Check the output which is sorted array
+        System.out.println(Arrays.toString(a));
+    }
+
+    @SuppressWarnings("rawtypes")
+    public static Comparable[] mergeSort(Comparable[] list)
+    {
+        //If list is empty; no need to do anything
+        if (list.length <= 1) {
+            return list;
+        }
+
+        //Split the array in half in two parts
+        Comparable[] first = new Comparable[list.length / 2];
+        Comparable[] second = new Comparable[list.length - first.length];
+        System.arraycopy(list, 0, first, 0, first.length);
+        System.arraycopy(list, first.length, second, 0, second.length);
+
+        //Sort each half recursively
+        mergeSort(first);
+        mergeSort(second);
+
+        //Merge both halves together, overwriting to original array
+        merge(first, second, list);
+        return list;
+    }
+
+    @SuppressWarnings({ "rawtypes", "unchecked" })
+    private static void merge(Comparable[] first, Comparable[] second, Comparable[] result)
+    {
+        //Index Position in first array - starting with first element
+        int iFirst = 0;
+
+        //Index Position in second array - starting with first element
+        int iSecond = 0;
+
+        //Index Position in merged array - starting with first position
+        int iMerged = 0;
+
+        //Compare elements at iFirst and iSecond,
+        //and move smaller element at iMerged
+        while (iFirst < first.length && iSecond < second.length)
+        {
+            if (first[iFirst].compareTo(second[iSecond]) < 0)
+            {
+                result[iMerged] = first[iFirst];
+                iFirst++;
+            }
+            else
+            {
+                result[iMerged] = second[iSecond];
+                iSecond++;
+            }
+            iMerged++;
+        }
+        //copy remaining elements from both halves - each half will have already sorted elements
+        System.arraycopy(first, iFirst, result, iMerged, first.length - iFirst);
+        System.arraycopy(second, iSecond, result, iMerged, second.length - iSecond);
+    }
+}
+