public class MyPlugin extends JavaPlugin{

    public void onEnable(){
        getServer().getPluginManager().registerEvents(new MyListener(this));
    }

}

public class MyListener implements Listener{

    private MyPlugin plugin;

    public MyListener(MyPlugin plugin){
        this.plugin = plugin;
    }

    @EventHandler
    public void onJoin(PlayerJoinEvent event){
        plugin.getLogger().info(event.getPlayer().getName()+" joined");
    }

}