Wat is hier fout aan?

package me.bukkit.knager;

import org.bukkit.plugin.java.*;
import org.bukkit.command.*;
import org.bukkit.entity.*;
import org.bukkit.*;

public final class Gamemode extends JavaPlugin {

    @Override
    public void onEnable() {
        this.getLogger().info("Plugin has been Enabled");

    }

    @Override
    public void onDisable() {
        this.getLogger().info("Plugin has been Disabled");
    }

    public boolean onCommand(final CommandSender sender, final Command cmd, final String Label, final String[] args) {
        if (cmd.getName().equalsIgnoreCase("gmc") && sender instanceof Player) {
            final Player player = (Player)sender;
            if (player.hasPermission("gamemode.creative")) {
                player.setGameMode(GameMode.CREATIVE);
                player.sendMessage(ChatColor.GRAY + "Je gamemode is veranderd naar:" + ChatColor.YELLOW + "Creative");
            }
            return true;

        if (cmd.getName().equalsIgnoreCase("gms") && sender instanceof Player) {
            final Player player = (Player)sender;
            if (player.hasPermission("gamemode.survival")) {
                player.setGameMode(GameMode.SURVIVAL);
                player.sendMessage(ChatColor.GRAY + "Je gamemode is veranderd naar:" + ChatColor.YELLOW + "Survival");
            }
            return true;

        if (cmd.getName().equalsIgnoreCase("gma") && sender instanceof Player) {
            final Player player = (Player)sender;
            if (player.hasPermission("gamemode.adventure")) {
                player.setGameMode(GameMode.ADVENTURE);
                player.sendMessage(ChatColor.GRAY + "Je gamemode is veranderd naar:" + ChatColor.YELLOW + "Adventure");
            }
            return true;

        if (cmd.getName().equalsIgnoreCase("gmsp") && sender instanceof Player) {
            final Player player = (Player)sender;
            if (player.hasPermission("gamemode.spectator")) {
                player.setGameMode(GameMode.SPECTATOR);
                player.sendMessage(ChatColor.GRAY + "Je gamemode is veranderd naar:" + ChatColor.YELLOW + "Spectator");
            }
            return true;
        }
    }
}

        return false;

        }
    }