Throttling is the process to control the rate at which data is received. In a Swing application, high frequency rates of data updates may cause painting events to be fired one after another, which may freeze the UI . We just need to avoid blocking the EDT (event dispatch thread) for a long time. In this example we will create a general purpose class to provide throttling. We will then apply throttling to JTable data updates.

Example

public class Throttler {
  private Timer timer;

  public Throttler(int rate, Runnable updater) {
      timer = new Timer(rate, new ActionListener() {
          @Override
          public void actionPerformed(ActionEvent e) {
              //this is already in EDT
              timer.stop();
              updater.run();
          }
      });
  }

  public void updateReceived() {
      //timer must be accessed by EDT  because actionPerformed is also invoked in EDT
      //otherwise we have to synchronized it. Not doing so might miss the events
      if (!SwingUtilities.isEventDispatchThread()) {
          throw new IllegalArgumentException("updateReceived() must be called in EDT");
      }

      if (!timer.isRunning()) {
          timer.restart();
      }
  }
}

Implementing Throttling to JTable

High frequency Data Service

public enum TestDataService {
  Instance;
  private String[] currencyPairs = {"EUR/USD", "USD/JPY", "GBP/USD",
          "USD/CHF", "USD/CAD", "AUD/USD", "NZD/USD", "EUR/GBP",
          "EUR/AUD", "GBP/JPY", "CHF/JPY", "NZD/JPY", "GBP/CAD"};


  public void listenToDataUpdate(BiConsumer<String, BigDecimal> forexListener) {
      ExecutorService es = Executors.newSingleThreadExecutor();
      es.execute(new Runnable() {
          @Override
          public void run() {
              while (true) {
                  int i = ThreadLocalRandom.current().nextInt(0, currencyPairs.length);
                  BigDecimal rate = BigDecimal.valueOf(Math.random() * 10);
                  rate = rate.setScale(2, RoundingMode.CEILING);
                  forexListener.accept(currencyPairs[i], rate);
                  try {
                      Thread.sleep(10);
                  } catch (InterruptedException e) {
                      e.printStackTrace();
                  }
              }
          }
      });
  }
}

Table Model

public class ForexTableModel extends AbstractTableModel {
  private Map<String, BigDecimal> forexRates = new TreeMap<>();
  private String[] columnNames = {"Currency Pair", "Rate"};

  public void updateRateWithoutFiringEvent(String currency, BigDecimal rate) {
      forexRates.put(currency, rate);
  }

  @Override
  public String getColumnName(int column) {
      return columnNames[column];
  }

  @Override
  public int getRowCount() {
      return forexRates.size();
  }

  @Override
  public int getColumnCount() {
      return columnNames.length;
  }

  @Override
  public Object getValueAt(int rowIndex, int columnIndex) {
     if (columnIndex == 0) {
          String currency = getCurrencyByRow(rowIndex);
          return currency;
      } else if (columnIndex == 1) {
          String currency = getCurrencyByRow(rowIndex);
          return forexRates.get(currency);
      }
      return null;
  }

  private String getCurrencyByRow(int rowIndex) {
      return forexRates.keySet()
                       .toArray(new String[forexRates.size()])[rowIndex];
  }
}

The main class

With throttling:

public class ThrottlingExampleMain {
  public static void main(String[] args) {
      ForexTableModel tableModel = new ForexTableModel();
      JTable table = new JTable(tableModel);
      listenToForexChanges(tableModel);
      JFrame frame = createFrame();
      frame.add(new JScrollPane(table));
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
  }

  private static void listenToForexChanges(ForexTableModel tableModel) {
      Throttler throttler = new Throttler(1000, new Runnable() {
          @Override
          public void run() {
              //it is in EDT
              tableModel.fireTableDataChanged();
          }
      });

      TestDataService.Instance.listenToDataUpdate(
              (pair, rate) -> SwingUtilities.invokeLater(() -> {
                  //table model must be accessed in EDT for thread safety
                  tableModel.updateRateWithoutFiringEvent(pair, rate);
                  throttler.updateReceived();
              }));
  }

  private static JFrame createFrame() {
      JFrame frame = new JFrame("Throttling Example");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setSize(new Dimension(500, 300));
      return frame;
  }
}

Without throttling:

public class WithoutThrottlingExample {
  public static void main(String[] args) {
      ForexTableModel tableModel = new ForexTableModel();
      JTable table = new JTable(tableModel);
      listenToForexChanges(tableModel);
      JFrame frame = createFrame();
      frame.add(new JScrollPane(table));
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
  }

  private static void listenToForexChanges(ForexTableModel tableModel) {
      TestDataService.Instance.listenToDataUpdate((pair, rate) -> {
          tableModel.updateRateWithoutFiringEvent(pair, rate);
          tableModel.fireTableDataChanged();
      });
  }

  private static JFrame createFrame() {
      JFrame frame = new JFrame("Without Throttling Example");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.setSize(new Dimension(500, 300));
      return frame;
  }
}

For a large number of rows, the screen will freeze without throttling.

Note that instead of using a class like Throttler, we can use a timer directly but the disadvantage of that approach will be that the timer will always be running even there's no updates.

Example Project

Dependencies and Technologies Used:

• JDK 1.8
• Maven 3.3.9