What is the right way to create thumbnail charts?

Question

I\'m trying to create a chart of thumbnails of some data with using JScrollPane, but I encounter performance difficulties. This example has about 100 thumbnails

Answer 1

Use the flyweight pattern to render only visible charts. The approach, used by JTable renderers, is outlined here and shown in the ChartRenderer seen below. For illustration, the dataset is recreated each time a cell is revealed; scroll, resize and switch applications to see the effect. While such rendering scales well into the tens of thousands of cells, each chart still renders N data points. You can limit the number of visible cells in the implementation of the Scrollable method, getPreferredScrollableViewportSize(), as shown below.

How to reduce memory usage to small values?

There is no general answer, but several strategies may prove helpful:

• Compose charts as early in program initialization as possible, rather than at the time they are rendered; the updated example below constructs a TableModel of ChartPanel instances; the ChartRenderer is correspondingly simpler.

• Charts having more than a few thousand points are effectively unreadable; consider truncating large datasets and displaying the full data only in response to a ListSelectionEvent, illustrated here.

• Platform activity monitors may be misleading; profile to verify actual results.

After starting applet it's not big, less than 200 Mb, but after scrolling, resizing etc. memory usage reaches values more than 600 Mb. Why?

A typical profiler view of the code below shows only moderate usage and the expected free/used ratio after scrolling and garbage collection; your results may vary.

import java.awt.Component;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.table.DefaultTableModel;
import javax.swing.table.TableCellRenderer;
import org.jfree.chart.ChartFactory;
import org.jfree.chart.ChartPanel;
import org.jfree.chart.JFreeChart;
import org.jfree.data.xy.XYSeries;
import org.jfree.data.xy.XYSeriesCollection;

/**
 * @see https://stackoverflow.com/a/40445144/230513
 */
public class ChartTable {

    private static final Random R = new Random();
    private static final int N = 5000;
    private static final int W = 200;
    private static final int H = W;

    private void display() {
        JFrame f = new JFrame("ChartTable");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        DefaultTableModel model = new DefaultTableModel(
            new String[]{"", "", "", ""}, 0) {
            @Override
            public Class<?> getColumnClass(int columnIndex) {
                return ChartPanel.class;
            }
        };
        for (int r = 0; r < 25; r++) {
            ChartPanel[] row = new ChartPanel[4];
            for (int c = 0; c < row.length; c++) {
                final XYSeries series = new XYSeries("Data");
                int n = R.nextInt(N);
                for (int i = 0; i < n; i++) {
                    series.add(i, R.nextGaussian());
                }
                XYSeriesCollection dataset = new XYSeriesCollection(series);
                JFreeChart chart = ChartFactory.createXYLineChart(
                    "Random " + series.getItemCount(), "Domain", "Range", dataset);
                ChartPanel chartPanel = new ChartPanel(chart) {
                    @Override
                    public Dimension getPreferredSize() {
                        return new Dimension(W, H);
                    }
                };
                row[c] = chartPanel;
            }
            model.addRow(row);
        }
        JTable table = new JTable(model) {
            @Override
            public Dimension getPreferredScrollableViewportSize() {
                return new Dimension(4 * W, 2 * H);
            }
        };
        table.setDefaultRenderer(ChartPanel.class, new ChartRenderer());
        table.setRowHeight(W);
        f.add(new JScrollPane(table));
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    private static class ChartRenderer implements TableCellRenderer {

        @Override
        public Component getTableCellRendererComponent(
            JTable table, Object value, boolean isSelected,
            boolean hasFocus, int row, int column) {
            return (ChartPanel) value;
        }
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new ChartTable()::display);
    }
}