Changing the Background Color for One Cell in a JTable

From:
Hal Vaughan <hal@halblog.com>
Newsgroups:
comp.lang.java.programmer
Date:
Sat, 19 Jan 2008 23:07:13 GMT
Message-ID:
<Bovkj.681$Yl.587@trnddc01>
I've been working on this for a few hours. I've read tutorials and seen
different examples, but this is still driving me nuts.

I have a table and want to be able to change the color of one cell in it.
It seems to do this, I can't get a cell renderer and just change the color,
I have to create my own class to do that. I've tried that and a number of
other things and can't get it to work.

I finally took the SimpleTableDemo from Sun and checked to make sure it was
running. Once it was, I added four lines:

        boolean isSelected = table.isCellSelected(1, 1);
        DefaultTableCellRenderer defRender = (DefaultTableCellRenderer)
                table.getCellRenderer(1, 1);
        Component cellRenderer = defRender.getTableCellRendererComponent(table,
                "Huml", isSelected, false, 1, 1);
        cellRenderer.setBackground(Color.blue);

(The whole example is at the bottom of this post.)

When I use this example, it turns ALL the cells in the table blue, not just
the one at 1,1.

I've got several questions about this:
1) Do I have to create my own cell renderer to change a cell background
color, or can't I just do it like above? Even when I used my own renderer,
I still got the actual Component named cellRenderer using the same
parameters, so what difference would doing it in a separate class make?
2) The renderer needs the value that is in the cell currently. In my own
program, I got that from the DefaultTableModel I was using. Here I just
used the text that was put in that cell. Is there any way to get the cell
value directly from the table? In this example, I tried getting a
DefaultTableModel (by casting) from the table, but it didn't work, so I
couldn't get the data by reading the cell.
3) Why does this code (above) set the entire table and not just the cell at
1,1?

If anyone has a simpler example of how to set the background color in just a
few lines, I'd be glad to see it. I can't believe how much I need to do
just to change the background color in one table cell!

Thanks for any help/insight!

Hal

----------------example code----------------

/*
 * SimpleTableDemo.java requires no other files.
 */

import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.table.DefaultTableCellRenderer;

import com.hal.gui.HalCellRenderer;

public class SimpleTableDemo extends JPanel {
    private boolean DEBUG = false;

    public SimpleTableDemo() {
        super(new GridLayout(1,0));

        String[] columnNames = {"First Name",
                                "Last Name",
                                "Sport",
                                "# of Years",
                                "Vegetarian"};

        Object[][] data = {
            {"Mary", "Campione",
             "Snowboarding", new Integer(5), new Boolean(false)},
            {"Alison", "Huml",
             "Rowing", new Integer(3), new Boolean(true)},
            {"Kathy", "Walrath",
             "Knitting", new Integer(2), new Boolean(false)},
            {"Sharon", "Zakhour",
             "Speed reading", new Integer(20), new Boolean(true)},
            {"Philip", "Milne",
             "Pool", new Integer(10), new Boolean(false)}
        };

        final JTable table = new JTable(data, columnNames);
        table.setPreferredScrollableViewportSize(new Dimension(500, 70));
// table.setFillsViewportHeight(true);

        if (DEBUG) {
            table.addMouseListener(new MouseAdapter() {
                public void mouseClicked(MouseEvent e) {
                    printDebugData(table);
                }
            });
        }

        //Create the scroll pane and add the table to it.
        JScrollPane scrollPane = new JScrollPane(table);

        //Add the scroll pane to this panel.
        add(scrollPane);

//======================================================
//Only part I have added is the next four lines
//======================================================
                boolean isSelected = table.isCellSelected(1, 1);
                DefaultTableCellRenderer defRender = (DefaultTableCellRenderer)
table.getCellRenderer(1, 1);
                Component cellRenderer =
defRender.getTableCellRendererComponent(table, "Huml", isSelected, false,
1, 1);
                cellRenderer.setBackground(Color.blue);
    }

    private void printDebugData(JTable table) {
        int numRows = table.getRowCount();
        int numCols = table.getColumnCount();
        javax.swing.table.TableModel model = table.getModel();

        System.out.println("Value of data: ");
        for (int i=0; i < numRows; i++) {
            System.out.print(" row " + i + ":");
            for (int j=0; j < numCols; j++) {
                System.out.print(" " + model.getValueAt(i, j));
            }
            System.out.println();
        }
        System.out.println("--------------------------");
    }

    /**
     * Create the GUI and show it. For thread safety,
     * this method should be invoked from the
     * event-dispatching thread.
     */
    private static void createAndShowGUI() {
        //Create and set up the window.
        JFrame frame = new JFrame("SimpleTableDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        //Create and set up the content pane.
        SimpleTableDemo newContentPane = new SimpleTableDemo();
        newContentPane.setOpaque(true); //content panes must be opaque
        frame.setContentPane(newContentPane);

        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
}

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