Hir mal den Richtigen Code:
1.
pm.registerEvents(new Join_Nachticht(), this);
2.
for (Player p2 : Bukkit.getOnlinePlayers()) {
if (p2 != e.getPlayer()) {
p2.sendMessage("§8[§a+§8] §a" + p.getName());
}
}
e.getPlayer().sendMessage("§aDu hast den Server betreten!");
e.getPlayer().playSound(e.getPlayer().getLocation(), Sound.BLOCK_NOTE_PLING, 1F, 1F);