public void setPieChart(JFreeChart pieChart) {
        if (pieChart == null) {
            throw new IllegalArgumentException("Null 'pieChart' argument.");
        }
        if (!(pieChart.getPlot() instanceof PiePlot)) {
            throw new IllegalArgumentException("The 'pieChart' argument must "
                    + "be a chart based on a PiePlot.");
        }
        this.pieChart = pieChart;
        fireChangeEvent();