用Java写一个Bukkit1201 玩家输入fly指令开启飞行的时候出现ActionBar文字消息关闭飞行的时候文字消失

你可以使用Bukkit的API来实现这个功能。下面是一个示例代码：

import org.bukkit.Bukkit;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerToggleFlightEvent;
import org.bukkit.plugin.java.JavaPlugin;

public class FlyMessagePlugin extends JavaPlugin implements Listener {

    @Override
    public void onEnable() {
        Bukkit.getPluginManager().registerEvents(this, this);
    }

    @Override
    public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
        if (command.getName().equalsIgnoreCase("fly")) {
            if (!(sender instanceof Player)) {
                sender.sendMessage("This command can only be executed by players.");
                return true;
            }
            Player player = (Player) sender;
            if (player.getAllowFlight()) {
                player.setAllowFlight(false);
                player.setFlying(false);
                player.sendMessage("Fly mode disabled.");
            } else {
                player.setAllowFlight(true);
                player.sendMessage("Fly mode enabled.");
            }
            return true;
        }
        return false;
    }

    @EventHandler
    public void onPlayerToggleFlight(PlayerToggleFlightEvent event) {
        Player player = event.getPlayer();
        if (player.getAllowFlight()) {
            if (player.isFlying()) {
                player.sendActionBar("You are flying.");
            } else {
                player.sendActionBar("");
            }
        }
    }
}

你可以将这个代码保存为一个Java文件，然后编译成插件。在玩家输入/fly指令时，会开启或关闭飞行模式，并显示相应的ActionBar消息。当玩家关闭飞行模式时，ActionBar消息会消失。