Java Swing, 2nd Edition

Charting Data with a TableModel

Our last example shows that the table machinery isn’t just for building tables; you can use it to build other kinds of components (like the pie chart in Figure 16-6). If you think about it, there’s no essential difference between a pie chart, a bar chart, and many other kinds of data displays; they are all different ways of rendering data that’s logically kept in a table. When that’s the case, it is easy to use a TableModel to manage the data and build your own component for the display.

With AWT, building a new component was straightforward: you simply created a subclass of Component. With Swing, it’s a little more complex because of the distinction between the component itself and the user-interface implementation. But it’s not terribly hard, particularly if you don’t want to brave the waters of the Pluggable L&F. In this case, there’s no good reason to make pie charts that look different on different platforms, so we’ll opt for simplicity. We’ll call our new component a TableChart; it extends JComponent. Its big responsibility is keeping the data for the component updated; to this end, it listens for TableModelEvents from the TableModel to determine when changes have been made.

To do the actual drawing, TableChart relies on a delegate, PieChartPainter. To keep things flexible, PieChartPainter is a subclass of ChartPainter, which gives us the option of building other kinds of chart painters (bar chart painters, etc.) in the future. ChartPainter ...