java - JTable inside JScrollPane: best height to disable scrollbars

Question

I am using the following code to create JTable inside JScrollPane to show column headers

JTable won't show column headers

String[] columnNames = {"header1", "header2", "header2", "header3"};
Object[][] data = new Object[num][4];
//feed values into data using for

JTable chart = new JTable(data, columnNames);
chart.setShowVerticalLines(false);
chart.setEnabled(false);
chart.setAutoResizeMode(JTable.AUTO_RESIZE_OFF);

JScrollPane sp = new JScrollPane(chart);
sp.setPreferredSize(new Dimension(width, chart.getHeight() + 5));
panel.add(sp);

The problem is that I need to compute a height for JScrollPane so the whole JTable can be visible and JScrollBars won't appear. How can I do that?

num changes from 2 to 4 and if it is 4 then scroll bars appear. width is fixed.

Answer 1

The basic approach is

• JTable is-a Scrollable which unfortunately doesn't do too well in calculating a prefScrollable, so you have to do it yourself
• either use a LayoutManager which lays out all at their pref (f.i. FlowLayout), or implement max in JTable (if you use a resizing but max-respecting manager like BoxLayout)
• JScrollPane is-a validationRoot, so the revalidate must happen on the parent of the scrollPane

Something like:

final JTable table = new JTable(10, 5) {

    @Override
    public Dimension getPreferredScrollableViewportSize() {
        Dimension dim = super.getPreferredScrollableViewportSize();
        // here we return the pref height
        dim.height = getPreferredSize().height;
        return dim;
    }

};
final JComponent content = new JPanel();
content.add(new JScrollPane(table));
Action add = new AbstractAction("add row") {

    @Override
    public void actionPerformed(ActionEvent e) {
        ((DefaultTableModel) table.getModel()).addRow(new Object[]{});
        content.revalidate();
    }
};