Initializing a HashSet from an Array or a Collection

Initialize hashset with values java – Initializing a HashSet from an Array or a Collection

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How to initialize a HashSet from an Array or a Collection in Java ?

Initialize hashset with values java: This article will give an clear idea about ho initialize a HashSet using a Array or a Collection. So let’s start the topic.

Java HashSet class has a constructor which receives a Collection as an argument and initializes the new Set with the elements of passed collection object. It contains unique elements only and stores data in a hash table using hashing mechanism.

public HashSet(Collection<? extends E> c)

Important :-

  • It inherits AbstractSet class
  • Implements Set interface
  • Duplicate values not allowed
  • But NULL elements are allowed
  • Also implements Serializable and Cloneable interfaces

Declaration of HashSet:

public class HashSet<E> extends AbstractSet<E> implements Set<E>, Cloneable, Serializable

Where,

  • HashSet extends Abstract Set<E>
  • HashSet implements Set<E>, Cloneable and Serializable interface
  • ‘E’ refers to types of elements which is maintained by the set.

We can do this by two ways i.e

Initializing a HashSet with an array :

As we know array is not a Collection, hence it is required to first convert this array into a List

If we have an array like

String[] Arr = {"Goa", "Puri", "Kochi", "Ranchi"};

It will be converted into list like this

List<String> arrList = Arrays.asList(Arr);

Below code represents an example to  initialize HashSet with String array

// Program :
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Iterator;
public class Main 
{
    public static void main(String args[])
    {
        // This is an array of String Objects
        String[] newArr = {"Goa", "Puri", "Kochi", "Ranchi"};
        // A new Set from an array is created
        HashSet<String> newSet = new HashSet<>(Arrays.asList(newArr));
        System.out.println(newSet);
    }
}
Output :
["Goa", "Puri", "Kochi", "Ranchi"]

Initializing a HashSet with an another HashSet :

It is achieved with the same HashSet constructor which receives another collection as an argument and adds all its element to the HashSet.

// Program :
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Iterator;
public class Main 
{
    public static void main(String[] args) 
    {
        // A new HashSet of String objects created
        HashSet<String> newSet = new HashSet<>();
        // Elements added in hashset
        newSet.add("Puri");
        newSet.add("Goa");
        newSet.add("Kochi");
        newSet.add("Ranchi");
        System.out.println("set Of Strings = " + newSet);
        // A new Set created and initialized it with existing HashSet
        HashSet<String> newStrSet = new HashSet<>(newSet);
        newSet.add("Delhi");
        newSet.add("Noida");
        System.out.println("");
        System.out.println("new String Set = " + newSet);
    }
}
Output :
set Of Strings = [Ranchi, Kochi, Goa, Puri]
new String Set = [Delhi, Ranchi, Kochi, Goa, Puri, Noida]