HashSet in Java Collection Example

• HashSet is a class of collection framework which extends AbstractSet class and implements the Set interface.
• HasSet doesn't guarantee that elements order will remain same over the time and returned in any random order.
• HasSet doesn't allow duplicate values. If you try to insert duplicate, It will overwrite.
• HasSet allows to store null values.
• HasSet implementation is not synchronized.

Important Methods of HashSet

• boolean add(E e) : To add elements in to set if it is not already present.
• void clear() : Remove all entries from set.
• Object clone() : It will returns shallow copy of HasSet instance.
• boolean contains(Object o) : It will return true if given values is present in HashSet.
• boolean isEmpty() : It will return true if HasSet is empty.
• Iterator<E> iterator() : It will returns an iterator over the elements in Set.
• boolean remove(Object o) : It will remove specified elements from set if it is available in HashSet.
• int size() : It will return size of HashSet.

Bellow given example will show you usage of different HashSet methods.

Example Of HashSet in Java

package JAVAExamples;

import java.util.HashSet;

public class HashSetJavaExample {
 public static void main(String args[]) {
 HashSet hset = new HashSet();
 //Check if HashSet is empty.
 System.out.println("HashSet is empty? : "+hset.isEmpty());
 //Add elements in HashSet.
 hset.add("One");
 hset.add("Two");
 hset.add("Three");
 hset.add(null); //HassSet allows null values.
 hset.add("Four");
 //Print HashSet.
 System.out.println("HashSet elements are : "+hset);
 //Check HashSet size.
 System.out.println("Size of HashSet is : "+hset.size());
 //Removing element from HashSet.
 hset.remove("Two");
 System.out.println("Now HashSet elements are : "+hset);
 }
}

Output :

HashSet is empty? : true
HashSet elements are : [null, One, Four, Two, Three]
Size of HashSet is : 5
Now HashSet elements are : [null, One, Four, Three]

This way, You can use HashSet to store values in random order including null.

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