Observer/Observable: update not called

[Timo Nentwig]

Hi!

Can somebody explain, why update() is not called on notifyObservers()?


public class Observe extends Observable
{
protected class IndexObserver implements Observer
{
public void update(Observable o, Object arg)
{
System.out.println("update()");
}
}

private IndexObserver indexObserver;

public Observe()
{
addObserver(indexObserver = new IndexObserver());
}

public void go()
{
notifyObservers();
}

public static void main(String[] args)
{
(new Observe()).go();
}
}

 

[Thomas Fritsch]

Hi!

Can somebody explain, why update() is not called on notifyObservers()?

Because you never call setChanged() on your Observable.
See the javadoc of method Observable#notifyObservers().

public class Observe extends Observable
{
protected class IndexObserver implements Observer
{
public void update(Observable o, Object arg)
{
System.out.println("update()");
}
}

private IndexObserver indexObserver;

public Observe()
{
addObserver(indexObserver = new IndexObserver());
}

public void go()
{
notifyObservers();
}

public static void main(String[] args)
{
(new Observe()).go();
}
}

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