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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
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]
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