I found a simple pie-chart class on the web. It works fine in normal use. I added implements TableCellRenderer and used it as a CellRenderer but the pie charts don't show in the cells. (For simplicity, the chart isn't yet connected to any data.)
It tried changing paint to paintComponent but it made no difference.
I've followed it through with the debugger: getTableCellRendererComponent is being executed for the right column in the JTable and paint is being called for each cell.
You wait all this time for a coincidence, then two come along at once...