The live bourse tracking system codes you created for the observer pattern usage example are as follows, but they do not work. I think the main function is missing. Complete it so it works and draw the uml diagram of the final version of the code.

$//$ Subject interface

public interface CurrencyRateTracker $\{$

void registerObserver$($Observer o$)$;

void removeObserver$($Observer o$)$;

void notifyObservers$()$;

$\}$

$//$ Concrete Subject

public class BourseRateTracker implements CurrencyRateTracker $\{$

private List observers $=$ new ArrayList$<>()$;

private double usdTryRate;

public void setUsdTryRate$($double rate$)\{$

this.usdTryRate $=$ rate;

notifyObservers$()$;

$\}$

@Override

public void registerObserver$($Observer o$)\{$

observers.add$($o$)$;

$\}$

@Override

public void removeObserver$($Observer o$)\{$

observers.remove$($o$)$;

$\}$

@Override

public void notifyObservers$()\{$

for $($Observer observer : observers$)\{$

observer.update$($usdTryRate$)$;

$\}$

$\}$

$\}$

$//$ Observer interface

public interface Observer $\{$

void update$($double usdTryRate$)$;

$\}$

$//$ Concrete Observer

public class CurrencyDisplay implements Observer $\{$

@Override

public void update$($double rate$)\{$

System.out.println$("$Updated USD$/$TRY Rate: $"+$ rate$)$;

$\}$

$\}$