Hazelcast Set is a distributed and concurrent implementation of java.util.Set.

  • Hazelcast Set does not allow duplicate elements.
  • Hazelcast Set does not preserve the order of elements.
  • Hazelcast Set is a non-partitioned data structure: all the data that belongs to a set will live on one single partition in that node.
  • Hazelcast Set cannot be scaled beyond the capacity of a single machine. Since the whole set lives on a single partition, storing large amount of data on a single set may cause memory pressure. Therefore, you should use multiple sets to store large amount of data; this way all the sets will be spread across the cluster, hence sharing the load.
  • A backup of Hazelcast Set is stored on a partition of another node in the cluster so that data is not lost in the event of a primary node failure.
  • All items are copied to the local node and iteration occurs locally.
  • The equals method implemented in Hazelcast Set uses a serialized byte version of objects, as opposed to java.util.HashSet.

Sample Set Code

import com.hazelcast.core.Hazelcast;
import java.util.Set;
import java.util.Iterator;

HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance();

Set<Price> set = hazelcastInstance.getSet( "IBM-Quote-History" );
set.add( new Price( 10, time1 ) );
set.add( new Price( 11, time2 ) );
set.add( new Price( 12, time3 ) );
set.add( new Price( 11, time4 ) );
Iterator<Price> iterator = set.iterator();
while ( iterator.hasNext() ) { 
  Price price =; 

Event Registration and Configuration for Set

Hazelcast Set uses ItemListener to listen to events which occur when items are added and removed.

import java.util.Queue;
import java.util.Map; 
import java.util.Set; 
import com.hazelcast.core.Hazelcast;
import com.hazelcast.core.ItemListener;
import com.hazelcast.core.EntryListener;
import com.hazelcast.core.EntryEvent; 

public class Sample implements ItemListener {

  public static void main( String[] args ) { 
    Sample sample = new Sample();
    HazelcastInstance hazelcastInstance = Hazelcast.newHazelcastInstance();
    ISet<Price> set = hazelcastInstance.getSet( "default" );
    set.addItemListener( sample, true ); 

    Price price = new Price( 10, time1 )
    set.add( price );
    set.remove( price );

  public void itemAdded( Object item ) {
    System.out.println( "Item added = " + item );

  public void itemRemoved( Object item ) {
    System.out.println( "Item removed = " + item );


To learn more about the configuration of listeners please refer to the Listener Configurations section.


Please refer to the Set Configuration section for a full description of Hazelcast Distributed Set configuration.