How to Merge an Array in a HashSet in Java

In this article we will discuss how to merge an array in a HashSet

HashSet has a member function addAll() that can add a collection into to a HashSet. But this Collection should be of Same Type as of HashSet or of its Base Class.

public boolean addAll(Collection<? extends E> c)


It will add the each element from given collection to HashSet one by one.

But an Array is not a Collection i.e.

String[] strArr = {"abc", "def", "ghi", "jkl"};

How to Merge an Array in HashSet?

For this we need to first convert our array into a Collection i.e. a List. We can do this using Arrays asList() function i.e.

public static <T> List<T> asList(T... a)

It returns a fixed size List with random access provision. asList() basically acts as an adapter for using non collection based data structure in Collection based APIs.

Now we can easily merge this given List into a HashSet using addAll() function i.e.


import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;

public class Example30 {

	public static void main(String[] args) {
		// Create a new HashSet of String objects
		HashSet<String> setOfStrs = new HashSet<>();
		// Adding elements in HashSet
		System.out.println("setOfStrs = " + setOfStrs);
		// Create an Array Of Strings
		String[] strArr = {"abc", "def", "ghi", "jkl"};
		// Convert the String array into a Collection i.e. List
		List<String> arrList = Arrays.asList(strArr);
		// Merge the HashSet and List 
		boolean bResult = setOfStrs.addAll(arrList);
			System.out.println("Merging of Set & ArrayList Successfull");
		System.out.println("setOfStrs = " + setOfStrs);



setOfStrs = [Hi, abc, hello, time]
Merging of Set & ArrayList Successfull
setOfStrs = [Hi, abc, def, ghi, jkl, hello, time]


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