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


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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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