How to add tooltips in JFreechart

I am doing the following to generate the stackedAreaChart

CategoryItemRenderer renderer = new StackedAreaRenderer();
CategoryPlot plot = new CategoryPlot();
plot.setDataset(dataset);
plot.setRenderer(renderer开发者_Python百科);
JFreeChart chart = new JFreeChart(plot);

how can I show the toop tips for the chart? Thanks.