Java swing concurrency, multiple propertychangelisteners?

Question

I have a panel called DataPanel which extends JPanel, and a worker called DataPanelWorker which extends SwingWorker.

Currently when I create the DataPanel, I start the DataPanelWorker which does some calculations and fires property changes after each calculation.

The DataPanel listens for these property changes and displays a message each time. eg "Calculation 1 complete" "Calculation 2 complete"

This works fine!

What I now want to do now is create a second instance of DataPanel (let's call this DataPanel2) but I want to use the original DataPanelWorker to save computation. I register DataPanel2 as another propertyChangeListener on DataPanelWorker.

My problem is I might register DataPanel2 after calculation 1 has been completed and the first propertyChangeEvent has been fired. How can I know how far through the worker is so that I can get DataPanel2 to be displaying the same messages as DataPanel1?

What I would like ideally is to keep a queue of propertyChangeEvents and when registering a new component, fire them all on just that component. Is there a standard way of doing this? Or am I looking at it from the wrong view?

Thanks

Answer 1

Conceptually, your SwingWorker should publish() interim instances of Calculation so that process() can update your DataModel and notify any listeners.

class DataPanelWorker extends SwingWorker<List<Calculation>, Calculation> {…}
class DataModel {
    private List<Calculation> list = new ArrayList<>();
    …
}

Your implementation of process() can then update your DataModel on the event dispatch thread . In this way, your DataModel always has the complete state of the calculation. Any listening DataPanel can ask the DataModel for the current List<Calculation> to display. Your DataModel can notify listeners of the arrival of new data using any of the approaches shown here . This example updates a JLabel ; this example also updates a chart; this example updates the TableModel of a listening JTable .

DataPanelWorker …does some calculations and fires property changes after each calculation.

Avoid firing property change events in your implementation of doInBackground() , as access to any shared data will need to be synchronized independently of the worker. Instead, update your DataModel in your implementation of process() , which synchronizes access for you. The DataModel can then fire events for registered listeners, knowing that updates will happen on the event dispatch thread .

Is there a way to pause the doInBackground() thread?

It's permitted, but you should't have to do so in this context. If necessary, multiple workers can cooperate as shown here .