Bukkit - Update a sign every second - scheduler

Question

I am trying to make a sign update every second, but I just don't know what to do.
I already have a finished code with a scheduler, but I just don't know where I should put it.
It would be very very nice if someone could help me or even give me an example code...
Here is my code:
public class Main extends JavaPlugin implements Listener{
DateFormat dFormat = new SimpleDateFormat("HH:mm");
Date d = new Date();
public void onEnable() {
System.out.println("[BookshelfDrop] BookshelfDrop v" + this.getDescription().getVersion() + " enabled");
getServer().getPluginManager().registerEvents(this, this);
}
public void onDisable() {
System.out.println("[BookshelfDrop] BookshelfDrop disabled");
}
#EventHandler
public void onChange(SignChangeEvent event) {
if (event.getLine(0).equalsIgnoreCase("[clock]")) {
Sign s = (Sign) event.getBlock().getState();
s.setLine(0, "[clock]");
Bukkit.getServer()
.getScheduler()
.scheduleSyncRepeatingTask(
Bukkit.getPluginManager().getPlugin("BookshelfDrop"),
new Runnable() {
public void run() {
s.setLine(1, "§a" + dFormat.format(d));
s.update();
}
}, 0, 20L);
}
}

Answer 1

You can create an ArrayList to put all your signs
public ArrayList<Sign> yourSigns = new ArrayList<Sign>();
Then add this to your onSignChange
public void onChange(SignChangeEvent event) {
if (event.getLine(0).equalsIgnoreCase("[clock]")) {
Sign s = (Sign) event.getBlock().getState();
yourSigns.add(s);
}
On your onEnable() method, you can then put your clock, making a loop through each sign on your signs list.