Question

我有时间序列图表。我的x轴是日期，Y轴只是数字。我试图在x轴上格式化日期，但是我一直在例外。我的代码如下：

        TimeSeries trueSeries = new TimeSeries("True Data");
        TimeSeries regressionSeries = new TimeSeries("Regression Line");
        TimeSeries averageSeries = new TimeSeries("Moving Average");

        for (Date date : regression.keySet()) {
            Calendar cal = Calendar.getInstance();
            cal.setTime(date);
            int month = cal.get(Calendar.MONTH) + 1;
            int day = cal.get(Calendar.DAY_OF_MONTH);
            int year = cal.get(Calendar.YEAR);
            regressionSeries.add(new Day(day, month, year),
                    regression.get(date));
            averageSeries.add(new Day(day, month, year),
                    movingAverage.get(date));
            trueSeries.add(new Day(day, month, year), trueData.get(date));
        }
        TimeSeriesCollection dataset = new TimeSeriesCollection();
        dataset.addSeries(trueSeries);
        dataset.addSeries(regressionSeries);
        dataset.addSeries(averageSeries);
        JFreeChart chart = ChartFactory.createXYLineChart(
                stock.getCompanyName() + " (" + stock.getTicker() + ")",
                "Date", // x-axis Label
                "Close Price", // y-axis Label
                dataset, // Dataset
                PlotOrientation.VERTICAL, // Plot Orientation
                true, // Show Legend
                true, // Use tooltips
                false // Configure chart to generate URLs?
                );

然后我尝试将x轴转换为简单的日期格式，如下所示：

XYPlot plot = (XYPlot) chart.getPlot();
DateAxis axis = (DateAxis) plot.getDomainAxis();
axis.setDateFormatOverride(new SimpleDateFormat("dd-MM-yyyy"));

当我运行时，我得到以下异常：

java.lang.ClassCastException：org.jfree.chart.axis.NumberAxis无法强制转换为org.jfree.chart.axis.DateAxis

有人可以告诉我我做错了吗？

Answer 1

根据Adding date/time to JFreeChart graph：

“...您正在使用ChartFactory.createXYLineChart()，为域名创建NumberAxis。而是使用ChartFactory.createTimeSeriesChart()，为域名创建DateAxis。” - trashgod

Answer 2

使用

XYPlot plot = (XYPlot) chart.getPlot();
DateAxis dateAxis = new DateAxis();
dateAxis.setDateFormatOverride(new SimpleDateFormat("dd-MM-yyyy")); 
plot.setDomainAxis(dateAxis);

XYPlot.setDomainAxis接受ValueAxis，它是DateAxis的父级。这样做可以避免错误。

JFreeChart日期轴格式问题

2 个答案: