package cloudsimulator.controllersimulator;

public class ClusterFormationController {
}

package cloudsimulator.controllersimulator;

import cloudsimulator.clustersimulator.ClusterManager;

public class ClusterFormationController {


    public void allocateVMs(long numberOfVmToAllocate, ClusterManager clusterManager) {
        clusterManager.getCluster().getTgGroup().stream()
                .findFirst()
                .ifPresent(tgGroup -> {
                    tgGroup.setVmNumber(tgGroup.getVmNumber() + numberOfVmToAllocate);
                });
    }


}

Add dummy logic in ClusterFormationController, just to increment the number of VMs.