Comment puis-je personnaliser la taille de JFreeChart dans un JPanel ?

JPanel graph = new JPanel(new GridLayout());
graph.add(new ChartPanel(chart, 500, 300));

ChartPanel cp = new ChartPanel(chart);
cp.setPreferredSize(new Dimension(500, 300));

@Override
public Dimension getPreferredSize() {
    return new Dimension(w, h);
}

public void generateChart() {
    DefaultCategoryDataset dataset = new DefaultCategoryDataset();

    //set the values of the chart
    for(int i=0; i<8; i++)
    {
        dataset.setValue(income_array[i], "Income",
            Double.toString(percent_array[i]));
    }

    JFreeChart chart = ChartFactory.createBarChart(
        "Required Annual Income for a Variety of Interest Rates",
        "Percent", "Income", dataset, PlotOrientation.VERTICAL,
        false,true, false);
    ChartPanel cp = new ChartPanel(chart, 500, 300);

    chart.setBackgroundPaint(Color.white);