Jazz Up Your JTables with Reusable Classes-4 : Page 4

Row and Cell Flashing
Following the pattern established by the ColorRenderer, you can set up custom renderer/provider pairs to manage fonts, borders, and other effects. Row and cell flashing is no different. In the Broker's Order display, rows flash whenever a price change occurs. A custom FlashColorRenderer and FlashProvider class/interface pair can control the flash effects:

public interface FlashProvider {
  public boolean isFlashOn(int row, int column);

};

As an example, create a FlashColorRenderer that uses the Decorator pattern just like the ColorRenderer. It should have a constructor that takes two arguments, the first a renderer and the second a FlashProvider:

public class FlashColorRenderer implements TableCellRenderer {

  protected TableCellRenderer delegate;
  protected FlashProvider provider;

  public FlashColorRenderer(TableCellRenderer anotherRenderer, 
    FlashProvider provider) {
    this.delegate = anotherRenderer;
    this.provider = provider;
  }
...
};

Inside the getTableCellRendererComponent() method, use the FlashProvider to get the flash state of a cell and then flash accordingly:

public Component getTableCellRendererComponent(...) {

    // Get the component from the delegate
    Component c =
      delegate.getTableCellRendererComponent(table, value, isSelected, 
      hasFocus, row, column);

    // Convert view column to model column
    int mcol = table.convertColumnIndexToModel(column);
    // invert the colours to flash
    if (provider.isFlashOn(row, mcol)) {
      Color bgrd = c.getForeground();
      Color fgrd = c.getBackground();
      c.setBackground(bgrd);
      c.setForeground(fgrd);
    }

    return c;

}

Wrap the FlashColorRenderer around the ColorRenderer so that you can use both effectively. Wrapping can continue endlessly—each layer adding its own specific behavior:

private void registerRendererForClass(JTable table,Class klass) {
    // Get Default Renderer from the table
    DefaultTableCellRenderer defaultRenderer =
      (DefaultTableCellRenderer) table.getDefaultRenderer(klass);
    // Wrap the color renderer around the default renderer
    TableCellRenderer colorRenderer = new ColorRenderer(defaultRenderer, provider);
    // Wrap the flash renderer around the colour renderer
    TableCellRenderer flashRenderer = new FlashColorRenderer(colorRenderer, 
    flashProvider);
    // Register our flash renderer with the table
    table.setDefaultRenderer(klass, flashRenderer);
  }

The final step to get the flashing feature working is to create a TableFlasher class that implements the FlashProvder interface to control the flash state of a cell (see Listing 2). Application code that updates order prices must also notify the TableFlasher of the update (Author's note: SWING is single threaded, so be sure to use the invokeLater() functionality when executing code that accesses UI components outside the Swing event thread.):

TableFlasher flashProvider = new TableFlasher(table);
...
// In a background thread, pick a row
int row = (int) (Math.random() * model.getRowCount());

// Generate a new price
Double price = new Double(Math.random() * 100);

// Update the OrderTableModel
model.updateOrderPrice(row, price); 

// Flash the price cell
flashProvider.flashCell(row, 2);
...

With the renderer, provider, and table model in place, a JTable display looks like Figure 3.

Figure 3: A Flashing Broker's Order Display

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