jfreechart 线条图不能出现工具提示

以下这个函数是产生chart对象的，但显示出来后就是没有tooltip出现：
private JFreeChart createCurveChart(ArrayList lst){
        XYDatasetCreator dsCreator=new XYDatasetCreator();
        dsCreator.addSeriesToDataset(CommonSeries.AVERAGE_VALUE,lst);
        dsCreator.addSeriesToDataset(CommonSeries.MAXIMUM_VALUE,lst);
        dsCreator.addSeriesToDataset(CommonSeries.MINIMUM_VALUE,lst);
        XYDataset dataset=dsCreator.getDs();
        
        JFreeChart chart = ChartFactory.createTimeSeriesChart("","时间","数量",dataset,true,true,false);        XYPlot plot=chart.getXYPlot();
        XYLineAndShapeRenderer renderer = (XYLineAndShapeRenderer) plot.getRenderer();
        renderer.setShapesVisible(true);
        renderer.setDrawOutlines(true);
        renderer.setItemLabelsVisible(true);
        //StandardXYToolTipGenerator tipCreator=new StandardXYToolTipGenerator("{1},{2}",new SimpleDateFormat(),new DecimalFormat("0.00"));
        StandardXYToolTipGenerator tipCreator=new StandardXYToolTipGenerator(StandardXYToolTipGenerator.DEFAULT_TOOL_TIP_FORMAT,new SimpleDateFormat(),new DecimalFormat("0.00"));
        renderer.setToolTipGenerator(tipCreator);
        plot.getRangeAxis().setLabelAngle(Math.PI / 2);
        ValueAxis domainAxis=plot.getDomainAxis();
        if(domainAxis instanceof DateAxis){
            if(dsCreator.getClassObj()==Day.class){
                DateAxis axis=(DateAxis)domainAxis;
                axis.setDateFormatOverride(new SimpleDateFormat("yyyy-MM-dd"));
            }
        }
        return chart;
    }