JList paint performance

Question

Hello all,
I I have a problem with JList painting.
I notiched that when I select cell in my list all the visible cells are repainted and not jas the selected cell.
After debugging I discovered that the paintion is done in the paint methot at the BasicListUI class.
I have a huge list which can display 100 cells on the screen at the same time and the so when I select one cell the painting causes my cpu usage to be at its maximum.
Unfortunally I don't know how to rewrite the UI in order to speed up cell painting for only the selected cells.
I'm using array list a the list model and the JList is configured as followed:
public class ButtonList extends JList
    public ButtonList()
        super();
        setCellRenderer(createCellRenderer());
        setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        setFixedCellHeight(Drawboard.getShapeHeight());
        setFixedCellWidth(Drawboard.getShapeWidth());
        setLayoutOrientation(HORIZONTAL_WRAP);
        setVisibleRowCount(0);
    protected ListCellRenderer createCellRenderer()
        return new ButtonCellRenderer();
}The list cell renderer is a JButton component:
public class ButtonCellRenderer extends JButton implements ListCellRenderer
    public ButtonCellRenderer()
        super();
        setOpaque(true);
    public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus)
            String val = value.toString();
            setText(val);
        setSelected(isSelected);
        return this;
    }Any suggestion?
Thanks in advance,
Hanoch

Answer 1

Hi michael,
I modified your test program so you could see what my problem is.
I set MyListUI as the ListUI of the ButtonList.
Now If you'll run the testing program you'll see on the console that when you press the one cell a lot of rows are repainted.
For example if you press the button with "0" and then the press the button with "47" than all of the cells between them are repainted.
My application is runnung on VIA800 with 256MB and I have 2 ButtonList like that on the screen so the user can choose Items from that list (This is a touch screen application). All of the unnecessary painting causes the CPU to be at its maximum.
import javax.swing.*;
import java.awt.*;
import javax.swing.event.*;
import javax.swing.plaf.basic.BasicListUI;
class Testing extends JFrame
    DefaultListModel listModel = new DefaultListModel();
    ButtonList list = new ButtonList(listModel);
    public Testing()
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        for (int x = 0; x < 200; x++)
            listModel.addElement("" + x);
        JScrollPane sp = new JScrollPane(list);
        sp.setPreferredSize(new Dimension(400, 75));
        getContentPane().add(sp);
        setSize(600, 800);
        setLocationRelativeTo(null);
    public static void main(String[] args)
        new Testing().setVisible(true);
class ButtonList extends JList
    public ButtonList(ListModel dataModel)
        super(dataModel);
        setCellRenderer(createCellRenderer());
        setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        setFixedCellHeight(90);
        setFixedCellWidth(90);
        setLayoutOrientation(HORIZONTAL_WRAP);
        setVisibleRowCount(0);
        setUI(new MyListUI());
    protected ListCellRenderer createCellRenderer()
        return new ButtonCellRenderer();
class ButtonCellRenderer extends JButton implements ListCellRenderer
    public ButtonCellRenderer()
        super();
        setOpaque(true);
    public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus)
        String val = value.toString();
        setText(val);
        setSelected(isSelected);
        return this;
class MyListUI extends BasicListUI
    public MyListUI()
        super();
    /* (non-Javadoc)
     * @see javax.swing.plaf.basic.BasicListUI#paint(java.awt.Graphics, javax.swing.JComponent)
    @Override
    public void paint(Graphics g, JComponent c)
        System.out.println("-----------------------");
        super.paint(g, c);
    /* (non-Javadoc)
     * @see javax.swing.plaf.basic.BasicListUI#paintCell(java.awt.Graphics, int, java.awt.Rectangle, javax.swing.ListCellRenderer, javax.swing.ListModel, javax.swing.ListSelectionModel, int)
    @Override
    protected void paintCell(Graphics g, int row, Rectangle rowBounds, ListCellRenderer cellRenderer, ListModel dataModel, ListSelectionModel selModel, int leadIndex)
        System.out.println("Row = " + row);
        super.paintCell(g, row, rowBounds, cellRenderer, dataModel, selModel, leadIndex);
}