"Team" system

When someone does /j their username gets added to an ArrayList, and when someone does /s I want it to divide them(people in arraylist) into 4 (kinda equal) teams, I'm guessing teams via permissions, but I don't know. How would I do this?

 

More information on what your are doing exactly?

 

Code:

public List<String>blueTeam = new ArrayList<String>();
public List<String>redTeam = new ArrayList<String>();
 
public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args){
    if(cmd.getName().equalsIgnoreCase("j")){
        if(sender instanceof Player){
            
            //
            
        } else {
        sender.sendMessage(ChatColor.DARK_RED + " You must be a player to do this! " );
    }
}

I don't know where to go from there for dividing it, but you should get the point