Find common elements among two unsorted arrays


Sometimes, you may face this situation that you have 2 arrays and both are unsorted. You need to compare them and find out the common values. How to find out common elements in 2 unsorted arrays?

Suppose, you are extracting data from Database as well as from front end¬†Application. Now, you need to compare the data extracted from both the sources.Let’s see with an example.

In the example below, we have 2 Integer arrays which are having some values. There are following steps which you will perform to complete the job.


  • Compare the length of both the array and find the small one.
  • Iterate through small array and put unique values in a HashSet.
  • Iterate through large array and find the elements stored in the previous Hashset.
  • If find common value, add to a new array.
  • Display final array.
package com.array;

import java.util.HashSet;

public class CommonValUnsortedArray {

	public static void main(String[] args) {
		Integer[ ] arrayFirst = { 4,3,7,2,4,0,8,2,5};
        Integer[ ] arraySecond = { 9,5,9,4,1};
        Integer[ ] commonValues = CommonValUnsortedArray.findCommonValues( arrayFirst, arraySecond );
        System.out.print( "Common Elements Between Two Arrays: " );       
        for( Integer vaule : commonValues ) {
            System.out.print( vaule + " " );   //Display the common values 

	public static Integer[ ] findCommonValues( Integer[ ] arrayFirst, Integer[ ] arraySecond ) {
    	Integer[ ] arrStoreCommon;
    	Integer[ ] arrayToSearch;

    	if( arrayFirst.length < arraySecond.length ) {
    		arrStoreCommon = arrayFirst;
    		arrayToSearch = arraySecond;
    	} else {
    		arrStoreCommon = arraySecond;
    		arrayToSearch = arrayFirst;

        HashSet<Integer> newArray = new HashSet<Integer>( );
        HashSet<Integer> hashedArray = new HashSet<Integer>( );
        //It will add only unique values into the HashSet
        for( Integer value : arrStoreCommon ) {
        //Check into another array , if value matches then add those values into a new HashSet
        for( Integer value : arrayToSearch ) {
            if( hashedArray.contains(value) ) {

        return newArray.toArray( new Integer[ 0 ] );



Common Elements Between Two Arrays: 4 5

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Shekhar Sharma

Shekhar Sharma is founder of This website is his window to the world. He believes that ,"Knowledge increases by sharing but not by saving".

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1 Response

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