import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerJoinEvent;

public class JoinMessage implements Listener
{
    @EventHandler
    public void onPlayerJoin(PlayerJoinEvent e)
    {
        Player p = e.getPlayer();

        e.setJoinMessage("Hi mum " + p.getName() + " has joined the server!");
    }
}