Java Program to Find Common Elements Between Two Arrays

There are multiple way to Find Common Elements Between Two Arrays.

Using for loop :-

First get two string java arrays.
Create HashSet object with string type.
Now iterate each of every elements one by one.
Inside if condition we compare first array element with second array element, if it is equal then add each common element in the HashSet for unique entry data.
After print the elements.

Using hashset and retailAll method :-

First we convert array element to list from Array.asList() method.
Now create two HashSet object and add the list element.
Use Collection.retainAll() method to find common elements.this method take only commons element of both the Hashset h1,h2 and keep in h1 HashSet.
Now prints the common elements.

				
					import java.util.Arrays;
import java.util.HashSet;

public class CommonELement {
	public static void main(String[] args) {

		String[] s1 = { "one", "two", "three", "five", "eight", "two" };
		String[] s2 = { "nine", "one", "eight", "ten", "five", "one" };
		HashSet<String> hs = new HashSet<String>();
		
		// from for loop
		for (int i = 0; i < s1.length; i++) {
			for (int j = 0; j < s2.length; j++) {
				if (s1[i].equals(s2[j])) {
					hs.add(s1[i]);
				}
			}
		}
		System.out.println("from for loop common elements are :- " + hs);
		
		// from hashset and retailAll method
		HashSet<String> h1 = new HashSet<String>(Arrays.asList(s1));
		HashSet<String> h2 = new HashSet<String>(Arrays.asList(s2));
		h1.retainAll(h2);
		System.out.println("from hashset and retailAll method common elements are :-" + h1);
	}
}

Output :-
from for loop common elements are :- [one, five, eight]
from hashset and retailAll method common elements are :- [one, five, eight]