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JavaFX – LineChart

June 22, 2009 12 comments

JavaFX 1.2 introduces new Chart APIs. Here we discuss about how to plot line chart using LineChart API.

For creating a chart, we need to create following instance

Note: Pie chart is an exception. In this case we don’t need to create instance of Series. Series is required only for X-Y chart types.

Lets implement a Line-Chart which updates its data dynamically. In this case a CPU monitor is simulated by generating random data from java class. The data is generated in a java Thread. The data is sent to JavaFX using a listener interface so as to update the chart. The notification is done via Event Dispatch Thread.

Update: Sample using live CPU and Memory information is available here.

For Applet mode, click on above image

For standalone mode

Create an instance of Series to plot chart for CPU usage of user, system and idle:


    var cpuLineChartSeries : LineChart.Series[] [
        LineChart.Series name: "User" },
        LineChart.Series name: "System" },
        LineChart.Series name: "Idle" }
    ];

Create an instance of Chart and associate the Series with this chart:


    var cpuLineChart = LineChart {
        
        title: "CPU Monitor"
        legendSide: Side.TOP
        showSymbols: false
        
        data: cpuLineChartSeries
        
        xAxis: NumberAxis {
            lowerBound: 1
            upperBound: 10
            tickUnit: 1
            label: "Minitues"
            tickMarkLength: 10
        }

        yAxis: NumberAxis {
            lowerBound: 0
            upperBound: 100
            tickUnit: 20
            label: "CPU %"
            tickMarkVisible: false
        }
        
        height: height
        width: width
    }

A simple UpdateListener interface is created. Which will be used to update data from java to javafx. Dummy CPU data is generated by CPUData class. The update is performed via Event Dispatch Thread using SwingUtilities.invokeLater( <Runnable> ).


    /**
     * Update listeners via Event Dispatch Thread
     */
    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            updateListener.updateCPU(user, sys, idle);
        }
    });

This update notification is handled in the JavaFX class and we can insert the data in chart as shown below.


    public override function updateCPU(user : Integer, sys : Integer, idle : Integer) {
        
        insert LineChart.Data 
            xValue: cpuIndex
            yValue: user
        into cpuLineChartSeries[0].data;

        insert LineChart.Data {
            xValue: cpuIndex
            yValue: sys
        into cpuLineChartSeries[1].data;

        insert LineChart.Data {
            xValue: cpuIndex
            yValue: idle
        into cpuLineChartSeries[2].data;

        cpuIndex += 1;
    }

When the index reaches the upper-bound, we can adjust the lowerBound and upperBound attributes of X-Axis, so as to shift the chart towards left. Also we may remove the initial chart data which are not visible.

Update:

As noted in comments section below, there is some Memory-Leak when we try to continuously update the bounds. Updation of bounds triggers updation of ticks and Skin related code of Label. For now instead of NumberAxis I have used a custom NoTickNumberAxis which supress the tick updates.


class NoTickNumberAxis extends NumberAxis {
    override function updateTickMarks() : Void {

    }
}

Try it out and let me know feedback!

Source:

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Categories: javafx Tags: , ,