可观察到的错误

Question

What does the error "The method setChanged() from type Observable is not visible" mean? I tried looking in the documentation and I didn't find anything for setting an observable object to visible. Here is my code:

       Observable observable = new Observable();
       //adding a listener to a button 
       @Override
        public void actionPerformed(ActionEvent e) {

            observable.setChanged();
            observable.notifyObservers(Main.this);

        }
    });

Answer 1

As defined in the API , the method setChanged is protected, and so available only to the class/subclasses:

protected void setChanged()

If you want to notify the observers about a change, call notifyObservers .