Java Observer Update function

Question

I have a class that implements observer, and of course it needs to have the update function:

public void update(Observable obs, Object obj);

Can someone please explain what do the two parameters stand for? Observable is my observable of course, but, how can I access my observable fields through this Observable obs object? And what is Object obj?

Answer 1

In case anybody else is experiencing difficulty in figuring out how to send that second parameter, it is as Nick points out: In the notifyObservers method call.

In the Observable:

private void setLicenseValid(boolean licenseValid) {
    this.licenseValid = licenseValid;
    setChanged();  // update will only get called if this method is called
    notifyObservers(licenseValid);  // add parameter for 2nd param, else leave blank
}

In the Observer:

@Override
public void update(Observable obs, Object arg) {
    if (obs instanceof QlmLicense) {
        setValid((Boolean) arg);
    }
}

Be sure to wire up your Observable correctly, else your update method will not get called.

public class License implements Observer {  
    private static QlmLicense innerlicense; 
    private boolean valid;
    private Observable observable;

    private static QlmLicense getInnerlicense() {
        if (innerlicense == null) {
            innerlicense = new QlmLicense();
            // This is where we call the method to wire up the Observable.
            setObservable(innerlicense);  
        }
        return innerlicense;
    }

    public boolean isValid() {
        return valid;
    }

    private void setValid(Boolean valid) {
        this.valid = valid;
    }

    // This is where we wire up the Observable.
    private void setObservable(Observable observable) {
        this.observable = observable;
        this.observable.addObserver(this);  
    }

    @Override
    public void update(Observable obs, Object arg) {
        if (obs instanceof InnerIDQlmLicense) {
            setValid((Boolean) arg);
        }
    }
}