Set
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.
Getting a Set and Putting Items
Use the HazelcastInstance getSet method to get the Set, then use the set put method to put items into the Set.
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 = iterator.next();
//analyze
}
RELATED INFORMATION
Please refer to the Set Configuration section for a full description of Hazelcast Distributed Set configuration.
Listening for Set Item Events
Hazelcast Set uses ItemListener to listen to events which occur when items are added and removed from the Set.
Use the set addItemListener method to create an ItemListener.
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 );
}
}
RELATED INFORMATION
To learn more about the configuration of listeners please refer to the Listener Configurations section.