Question

I’m trying to plot a step chart with the following properties:
x-axis: Time (ms) [Actual data contains this as a double value]
y-axis: Another value stored as an integer.

I’m filling up the dataset as follows:

private XYSeries populateStepChartDataSet(HashMap<Double, Integer> dataGrid){
    XYSeries xySeries = new XYSeries("Step Plot", true, true);

    if(dataGrid != null){
        for (Double timeStamp : dataGrid.keySet()) {
            xySeries.add(timeStamp, dataGrid.get(timeStamp));
        }
    }

    return xySeries;
}

And the section where I create the plot is as follows:

        final XYSeriesCollection dataset = new XYSeriesCollection();
        dataset.addSeries(populateStepChartDataSet(dspDataGrid));

        final JFreeChart chart = ChartFactory.createXYStepChart(
            title,
            xAxisLabel, yAxisLabel,
            dataset,
            PlotOrientation.VERTICAL,
            true,   // legend
            true,   // tooltips
            false   // urls
        );

What I expect is the plot to show time in ms at the x-axis but this value is getting converted to some weird time. Here’s how the plot looks

Can someone please help me get back the timestamp in ms format for the x-axis?

Answer 1

It looks like the x Axis is formatting as a date one way of adressing this is to provide a NumberFormatOverride

Add this code after your chart is created:

XYPlot plot = (XYPlot)chart.getPlot();
plot.setDomainAxis(0, new NumberAxis()); 
NumberAxis axis = (NumberAxis) plot.getDomainAxis();
axis.setNumberFormatOverride( new NumberFormat(){

    @Override
    public StringBuffer format(double number, StringBuffer toAppendTo, FieldPosition pos) {

    return new StringBuffer(String.format("%f", number));
    }

    @Override
    public StringBuffer format(long number, StringBuffer toAppendTo, FieldPosition pos) {
    return new StringBuffer(String.format("%9.0f", number));
    }

    @Override
    public Number parse(String source, ParsePosition parsePosition) {
    return null;
    }
    } );
    axis.setAutoRange(true);
    axis.setAutoRangeIncludesZero(false);

You shold then get this chart: