如果玩家键入 /launch，我如何让我的代码向玩家返回“无效号码”消息<notaninteger>或 /launch 字符串</notaninteger>

Question

import org.bukkit.ChatColor;
import org.bukkit.command.Command;
import org.bukkit.command.CommandExecutor;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;


public class launch implements CommandExecutor {
    @Override
    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
        if (label.equalsIgnoreCase("launch") || label.equalsIgnoreCase("l")) {
            if (!(sender instanceof Player)) {
                sender.sendMessage(ChatColor.translateAlternateColorCodes('&', "&7[&dHi&bMessage&7]  &4Invalid Entity"));
                return true;
            }
            Player player = (Player) sender;
            //Does /launch or /launch <amplifier>
            if (args.length == 0) {
                player.sendMessage(ChatColor.translateAlternateColorCodes('&', "&7[&dHi&bMessage&7]  &2Launching in &a3"));
                try {
                    Thread.sleep(1000);
                    player.sendMessage(ChatColor.translateAlternateColorCodes('&', "&7[&dHi&bMessage&7]  &2Launching in &62"));
                } catch (InterruptedException e) {
                    System.err.println(e.getMessage());
                }
                try {
                    Thread.sleep(1000);
                    player.sendMessage(ChatColor.translateAlternateColorCodes('&', "&7[&dHi&bMessage&7]  &2Launching in &c1"));
                } catch (InterruptedException e) {
                    System.err.println(e.getMessage());
                }
                player.setVelocity(player.getLocation().getDirection().multiply(2).setY(1.5));
                return true;
            }


            //Launch but with args
            player.sendMessage(ChatColor.translateAlternateColorCodes('&', "&7[&dHi&bMessage&7]  &2Launching in &a3"));
            try {
                Thread.sleep(1000);
                player.sendMessage(ChatColor.translateAlternateColorCodes('&', "&7[&dHi&bMessage&7]  &2Launching in &62"));
            } catch (InterruptedException e) {
                System.err.println(e.getMessage());
            }
            try {
                Thread.sleep(1000);
                player.sendMessage(ChatColor.translateAlternateColorCodes('&', "&7[&dHi&bMessage&7]  &2Launching in &c1"));
            } catch (InterruptedException e) {
                System.err.println(e.getMessage());
            }
            player.setVelocity(player.getLocation().getDirection().multiply(Integer.parseInt(args[0])).setY(1.5));
            player.setHealth(20.0);

            return true;
        }
    return false;
    }}

Maybe I could add like a if statement or a catch with a NonIntegerException? And please do be patient, as I am a new young developer and I have seen how people get upset/angry if someone does not know how to format a question correctly. Once again, as in the title, my question is: How can I make my code return a "Invalid number" message to a player if they type /launch or /launch String

Answer 1

After "//Launch but with args" you have to check if args[0] is an integer. I'd suggest to define a method for that like:

public boolean isInteger(String arg) {
        try {
            Integer.parseInt(arg);
        } catch (NumberFormatException e) {
            return false;
        }
        return true;
}

Then before starting the countdown you could add something like this:

if (!isInteger(args[0])) {
    player.sendMessage("Invalid number");
    return true;
}