added merge sort in java (#42)

sorting/README.md

@@ -24,6 +24,7 @@
 1. [Bubble Sort](java/bubble-sort.java)
 2. [Insertion Sort](java/insertion-sort.java)
 3. [Selection Sort](java/selection-sort.java)
+4. [Merge Sort](java/merge-sort.java)
 
 ### JavaScript
 

sorting/java/merge-sort.java

@@ -0,0 +1,79 @@
+//Java program for implementation of Merge Sort
+import java.util.*;
+
+class MergeSortApp
+{
+	private int[] arr;
+	public MergeSortApp()
+	{		
+		arr = new int[]{12,54,222,54622,10,169,30}; //Array to sort
+	}
+
+    //Funtion to display/Print Array
+	public void printArray()
+	{
+	for (int i=0;i<arr.length;i++)
+		{
+			System.out.print(arr[i]+ " ");
+		}
+		System.out.println();
+	}
+
+	//Function called by main()	
+	public  void mergesort()
+	{
+		int[] wr = new int[arr.length];  //Provides workspace
+		recMergeSort(wr,0,wr.length-1);
+	}
+
+	//Recursive function to divide array in halves	
+	public void recMergeSort(int[] wr,int lowBound,int uppBound)
+	{
+	if (lowBound == uppBound) 
+		return;
+	else
+	{
+		int mid = (lowBound+uppBound)/2; //find midpoint
+		recMergeSort(wr,lowBound,mid);   //Sort low half
+		recMergeSort(wr,mid+1,uppBound); // Sort high half
+		merge(wr,lowBound,mid+1,uppBound); //merge them
+	}
+	}
+
+	//Function to merge sorted Arrays	
+	public  void merge(int[] wr,int lowptr,int highptr, int uppBound)
+	{
+	
+			int j=0;
+			int lowBound = lowptr;
+			int mid = highptr-1;
+			int n = uppBound-lowBound+1;
+
+	while (lowptr<=mid && highptr<=uppBound)
+	{		if (arr[lowptr]<arr[highptr])
+				wr[j++] = arr[lowptr++];
+			else
+				wr[j++]	= arr[highptr++];
+	}
+	while (lowptr<=mid)
+		wr[j++] = arr[lowptr++];
+
+	while(highptr<=uppBound)
+		wr[j++] = arr[highptr++];
+
+
+	for (j=0;j<n;j++)
+		arr[lowBound+j] = wr[j];
+	}
+}	
+
+class MergeSort 
+{		//Driver code to test above code
+		public static void main(String[] args) 
+		{
+				MergeSortApp ob = new MergeSortApp(); //creates object
+				ob.printArray();	//Displays Array before sorting
+				ob.mergesort();
+				ob.printArray();
+		}
+}