Publish Your Article Here

Program: Implement merge sort in java.

Merge sort is a divide and conquer algorithm.

Steps to implement Merge Sort:

1) Divide the unsorted array into n partitions, each partition contains 1 element. Here the one element is considered as sorted.
2) Repeatedly merge partitioned units to produce new sublists until there is only 1 sublist remaining. This will be the sorted list at the end.

Merge Sort

Merge sort is a fast, stable sorting routine with guaranteed O(n*log(n)) efficiency. When sorting arrays, merge sort requires additional scratch space proportional to the size of the input array. Merge sort is relatively simple to code and offers performance typically only slightly below that of quicksort.

package com.java2novice.sorting;

public class MyMergeSort {
	private int[] array;
	private int[] tempMergArr;
	private int length;

	public static void main(String a[]){
		int[] inputArr = {45,23,11,89,77,98,4,28,65,43};
		MyMergeSort mms = new MyMergeSort();
		for(int i:inputArr){
	    	System.out.print(" ");
	public void sort(int inputArr[]) {
		this.array = inputArr;
		this.length = inputArr.length;
		this.tempMergArr = new int[length];
		doMergeSort(0, length - 1);

	private void doMergeSort(int lowerIndex, int higherIndex) {
		if (lowerIndex < higherIndex) {
			int middle = lowerIndex + (higherIndex - lowerIndex) / 2;
			// Below step sorts the left side of the array
			doMergeSort(lowerIndex, middle);
			// Below step sorts the right side of the array
			doMergeSort(middle + 1, higherIndex);
			// Now merge both sides
			mergeParts(lowerIndex, middle, higherIndex);

	private void mergeParts(int lowerIndex, int middle, int higherIndex) {

		for (int i = lowerIndex; i <= higherIndex; i++) {
			tempMergArr[i] = array[i];
		int i = lowerIndex;
		int j = middle + 1;
		int k = lowerIndex;
		while (i <= middle && j <= higherIndex) {
			if (tempMergArr[i] <= tempMergArr[j]) {
				array[k] = tempMergArr[i];
			} else {
				array[k] = tempMergArr[j];
		while (i <= middle) {
			array[k] = tempMergArr[i];


4 11 23 28 43 45 65 77 89 98 
<< Previous Program 
blog comments powered by Disqus

Java Sorting Algorithms Examples

  1. Implement bubble sort in java.
  2. Implement selection sort in java.
  3. Implement insertion sort in java.
  4. Implement quick sort in java.
  5. Implement merge sort in java.
Knowledge Centre
Pass by value Vs Pass by reference
Pass by value: Passing a copy of the value, not the original reference.

Pass by reference: Passsing the address of the object, so that you can access the original object.
Famous Quotations
Education is what remains after one has forgotten what one has learned in school.
-- Albert Einstein

About Author

Most Visited Pages

Other Interesting Sites

Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
Privacy Policy | Copyright © 2017 by Nataraja Gootooru. All Rights Reserved.