With the SortedList implementation of ObservableList, automatically sorting a JavaFX TableView nearly works out of the box. In fact, it does work out of the box as long as you are adding or removing items from the list. In these circumstances, the list and the accompanying TableView will automatically resort the data. The case where the data isn’t automatically resorted is if the data in the existing rows change, but no rows are added or removed from the list.

For example, I have a TableView displaying various price information about a list of stocks including the last price, and the percent change from yesterday’s closing price. I would like to sort the list based on percent change, from lowest to highest as the prices change in real-time.  However since the app just loads the stocks into the list once and then never adds or removes items from the list, the TableView only auto sorted on the initial load, but did not automatically sort as the prices were updated.

Fortunately the fix proved to be fairly minor and easy to implement.

To start with, the application uses a Stock POJO which contains the following properties to represent the data. An ObservableList of these POJOs will be the basis of the data that the TableView will render.

public class Stock implements Level1QuoteListener {

protected StockTicker ticker;

protected SimpleStringProperty symbol = new SimpleStringProperty("");

protected SimpleDoubleProperty bid = new SimpleDoubleProperty(0);

protected SimpleDoubleProperty ask = new SimpleDoubleProperty(0);

protected SimpleDoubleProperty last = new SimpleDoubleProperty(0);

protected SimpleDoubleProperty percentChange = new SimpleDoubleProperty(0);

protected SimpleIntegerProperty volume = new SimpleIntegerProperty(0);

protected SimpleDoubleProperty previousClose = new SimpleDoubleProperty(0);

protected SimpleDoubleProperty open = new SimpleDoubleProperty(0);

The first step is to implement a new Callback, tying it to the property we wish to sort in the table. When this property is updated it will trigger the table to resort itself automatically.

      Callback<Stock,Observable[]> cb =(Stock stock) -> new Observable[]{
        stock.percentChangeProperty(),
    };

The next step is to create a new ObservableList using the Callback above.

      ObservableList<Stock> observableList = FXCollections.observableArrayList(cb);
      observableList.addAll(stocks);

Finally the last step is to create a new SortedList using the ObservableList previously created and also passing in an implementation of a Comparator which will be used to determine how to sort the data.

      SortedList<Stock> sortedList = new SortedList<>( observableList, 
      (Stock stock1, Stock stock2) -> {
        if( stock1.getPercentChange() < stock2.getPercentChange() ) {
            return -1;
        } else if( stock1.getPercentChange() > stock2.getPercentChange() ) {
            return 1;
        } else {
            return 0;
        }
    });


    tickerTableView.setItems(sortedList);
}

That’s it. The video below illustrates the auto-sorting in action as the price of the stocks are updated in real-time.

twitter: @RobTerpilowski