In this article, we will discuss how to find size or length of HashSet

HashSet :

We can use, size() method of Collection interface to find size of an HashSet which

• stores only unique elements
• allows maximum of one null element
• stores elements in random-order

To get size of HashSet using size() method :

FindSizeOfHashSet.java

package in.bench.resources.java.collections;

import java.util.HashSet;
import java.util.Iterator;

public class FindSizeOfHashSet {

	public static void main(String[] args) {

		// creating HashSet object of type String
		HashSet<String> hs = new HashSet<String>();

		// adding elements to HashSet object
		hs.add("Sundar Pichai");
		hs.add("Satya Nadella");  
		hs.add("Shiv Nadar");  
		hs.add("Shantanu Narayen");
		hs.add("Sundar Pichai"); // duplicate object
		hs.add("Francisco D’Souza");
		hs.add(null); // one null is allowed
		hs.add(null); // Again, null is allowed - duplicate

		int hashSetSize = hs.size();

		System.out.println("Size of an HashSet is : " + hashSetSize);

		// Iterating using Iterator of Collection interface
		System.out.println("\n\nIterating HashSet elements\n");
		Iterator<String> itr = hs.iterator();
		while(itr.hasNext()) {
			System.out.println(itr.next());
		}
	}
}

Output:

Size of an HashSet is : 6


Iterating HashSet elements

null
Shantanu Narayen
Shiv Nadar
Sundar Pichai
Satya Nadella
Francisco D’Souza

From above example, HashSet

• doesn’t allow duplicate elements
• maximum of one null object is allowed
• while iterating, retrieve elements in random-order

References:

• https://docs.oracle.com/javase/tutorial/collections/intro/
• https://docs.oracle.com/javase/tutorial/collections/interfaces/collection.html
• https://docs.oracle.com/javase/7/docs/api/java/util/Collection.html
• https://docs.oracle.com/javase/tutorial/collections/interfaces/set.html
• https://docs.oracle.com/javase/7/docs/api/java/util/Set.html
• https://docs.oracle.com/javase/7/docs/api/java/util/class-use/HashSet.html
• https://docs.oracle.com/javase/7/docs/api/java/util/HashSet.html
• https://docs.oracle.com/javase/7/docs/api/java/util/Iterator.html
• https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html

Happy Coding !!
Happy Learning !!