Initialize HashSet in Java

A set is a collection which does not allows duplicate values. HashSet is an implementation of a Set. Following are the ways in which we can initialize a HashSet in Java.

• Using constructor − Pass a collection to Constructor to initialize an HashSet.

• Using addAll() − Pass a collection to Collections.addAll() to initialize an HashSet.

• Using unmodifiableSet() − Pass a collection to Collections.unmodifiableSet() to get a unmodifiable Set.

• Using add() − Using add(element) method of Set.

Following is an example of using above ways.

Example

Infinity

Now consider the following code snippet.

Example

 Live Demo

import java.util.Arrays; import java.util.Collections; import java.util.HashSet; import java.util.List; import java.util.Set; public class Tester{    public static void main(String[] args) {       List<Integer> list = Arrays.asList(1,2,3,4,5,6);       //Scenario 1       Set<Integer> set1 = new HashSet<>(list);       System.out.println(set1);       //Scenario 2       Set<Integer> set2 = new HashSet<>(list);       Collections.addAll(set2, 1,2,3,4,5,6);       System.out.println(set2);       //Scenario 3       Set<Integer> set3 = Collections.unmodifiableSet(set2);       System.out.println(set3);       //Scenario 4       Set<Integer> set4 = new HashSet<>();       set4.add(1);set4.add(2);set4.add(3);       set4.add(4);set4.add(5);set4.add(6);       System.out.println(set4);    } }

Output

[1, 2, 3, 4, 5, 6] [1, 2, 3, 4, 5, 6] [1, 2, 3, 4, 5, 6] [1, 2, 3, 4, 5, 6]