Variables Being Reset.

Code:java

public HashSet<String> xenos = new HashSet<String>();
 
@EventHandler
public void xenoDoubleJump(PlayerToggleFlightEvent event)
    {
    System.out.print(xenos.size()); //DEBUGGING PURPOSES
    if(event.isFlying() && xenos.contains(event.getPlayer().getName()))
        {
        System.out.print("test"); //DEBUGGING PURPOSES
        event.getPlayer().setFlying(false);
        event.getPlayer().setVelocity(event.getPlayer().getLocation().getDirection().setY(1.1));
        //    CHANGE THE 1.1 SO IT BECOMES INCREASINGLY INCREMENTAL AS THE GAME TIME INCREASES    \\
        }
 
    }
 
@EventHandler
public void xenoMovement(PlayerMoveEvent event)
    {
    if(xenos.contains(event.getPlayer().getName()))
        event.getPlayer().setVelocity(event.getPlayer().getLocation().getDirection().multiply(2));
    //        CHANGE THE 2 SO IT BECOMES INCREASINGLY INCREMENTAL AS THE GAME TIME INCREASES        \\
    }
 
public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args)
    {
    if(!(sender.isOp()) || !(sender instanceof Player)) return false;
    Player player = (Player) sender;
 
    if(xenos.contains(player.getName()))
        {
        player.setAllowFlight(false);
        xenos.remove(player.getName());
        }
 
    else
        {
        player.setAllowFlight(true);
        xenos.add(player.getName());
        }
 
    System.out.print(xenos.size()); //DEBUGGING PURPOSES
    return true;
    }

So every time you do the /xeno command it should add the player's name to the HashSet, which it does because after I do the command it prints out the size of the HashSet as 1, however, when I try to fly it displays it as 0, as if it got reset. Can someone tell me what I'm doing wrong to cause it to reset like that? Thanks.

 

@danhthonywalker

Try using an ArrayList instead of a HashSet