Plugin help for someone

package me.Envy.plugs;

import org.bukkit.ChatColor;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.plugin.java.JavaPlugin;

public class basics extends JavaPlugin{

    public boolean onCommand(CommandSender sender, Command cmd, String commandLabel, String[] args){
        if(commandLabel.equalsIgnoreCase("fly")){
            if(sender instanceof Player){ // Check if the sender is a player
                if(args.length == 1){ // Check if argument on/off is given, length 1 means given
                    Player player = (Player) sender; // Cast the sender to a player
                    if(args[0].equalsIgnoreCase("on")){ // Check if first argument is on
                        player.setAllowFlight(true); // Allow them to fly
                        player.sendMessage(ChatColor.GREEN + "Fly enabled!");
                    }else if(args[0].equalsIgnoreCase("off")){ // Check if first argument is off
                        player.setAllowFlight(false); // Disallow them to fly
                        player.sendMessage(ChatColor.GREEN + "Fly disabled!");
                    }else{ // First argument incorrect
                        sender.sendMessage(ChatColor.RED + "/fly <on/off>");
                    }
                }else{ // Correct length not given
                    sender.sendMessage(ChatColor.RED + "/fly <on/off>");
                }
            }else{
                sender.sendMessage(ChatColor.RED + "Only players can use that command."); // If not, tell them
            }
        }
        return true;
    }
}