java - Changing Cell Color without changing color in other cells (Jtable)

Question

So say that we have a JTable with 31 columns and 10 rows. And I want to change the color of the 2 Column 4 row to red. And after I do that change another cell color without loosing the color of my previous cell.

I have tried the following without success:

public class CellR extends DefaultTableCellRenderer {

     public Component getTableCellRendererComponent(JTable table,
            Object value, boolean isSelected, boolean hasFocus,
            int row, int column) {

        setForeground(Color.white);
        if(row == TestHotel.v.getRow()  && column == TestHotel.v.getCol()){
            // Only for specific cell
            // c.setFont(/* special font*/);
            // you may want to address isSelected here too
            setForeground(Color.BLACK);
            setBackground(Color.RED);
         } 
         return this;
}

If I call the renderer the first time it is working... But if I then want to change another cell color I am loosing the first one.

Answer 1

The cell renderers in tables and lists are used like a "stamp". One component is used for painting all the cells. Also see Concepts: Editors and Renderers. If you want to retain the information about the "highlighted" cells, you somehow have to store them.

An example (extended based on the comments) :

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Point;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.SwingUtilities;
import javax.swing.table.DefaultTableCellRenderer;
import javax.swing.table.TableColumn;
import javax.swing.table.TableColumnModel;

public class CellRendererTest
{
    public static void main(String[] args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            @Override
            public void run()
            {
                createAndShowGUI();
            }
        });
    }

    private static void createAndShowGUI()
    {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        String[] columnNames = {
            "First Name", "Last Name", "Sport" };
        Object[][] data = {
            {"Kathy", "Smith", "Snowboarding" },
            {"John", "Doe", "Rowing" },
            {"Sue", "Black", "Knitting"},
            {"Jane", "White", "Speed reading"},
            {"Joe", "Brown", "Pool"}
        };
        final JTable table = new JTable(data, columnNames);

        final ColoringCellRenderer cellRenderer = new ColoringCellRenderer(); 
        TableColumnModel columnModel = table.getColumnModel();
        int cc = columnModel.getColumnCount();
        for (int c=0; c<cc; c++)
        {
            TableColumn column = columnModel.getColumn(c);
            column.setCellRenderer(cellRenderer);
        }
        JScrollPane scrollPane = new JScrollPane(table);
        f.getContentPane().setLayout(new BorderLayout());
        f.getContentPane().add(scrollPane, BorderLayout.CENTER);

        JButton addRandomColorButton = new JButton("Add random color");
        addRandomColorButton.addActionListener(new ActionListener()
        {
            private Random random = new Random(0);
            @Override
            public void actionPerformed(ActionEvent e)
            {
                int rows = table.getRowCount();
                int cols = table.getColumnCount();
                int row = random.nextInt(rows);
                int col = random.nextInt(cols);
                int r = random.nextInt(255);
                int g = random.nextInt(255);
                int b = random.nextInt(255);
                cellRenderer.setCellColor(row, col, new Color(r,g,b));
                table.repaint();
            }
        });
        f.getContentPane().add(addRandomColorButton, BorderLayout.SOUTH);

        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }
}


class ColoringCellRenderer extends DefaultTableCellRenderer
{
    private final Map<Point, Color> cellColors = new HashMap<Point, Color>();

    void setCellColor(int r, int c, Color color)
    {
        if (color == null)
        {
            cellColors.remove(new Point(r,c));
        }
        else
        {
            cellColors.put(new Point(r,c), color);
        }
    }

    private Color getCellColor(int r, int c)
    {
        Color color = cellColors.get(new Point(r,c));
        if (color == null)
        {
            return Color.WHITE;
        }
        return color;
    }

    @Override
    public Component getTableCellRendererComponent(JTable table, Object value,
        boolean isSelected, boolean hasFocus, int row, int column)
    {
        super.getTableCellRendererComponent(
            table, value, isSelected, hasFocus, row, column);
        Color color = getCellColor(row, column);
        setBackground(color);
        return this;
    }
}

---

EDIT: The remaining part was from the original answer, using only a single cell color. The new one above is more complete (and more powerful, because it can emulate the single-color renderer), but I'll leave this here for completeness

This could be achieved with a renderer like this one:

class ColoringCellRenderer extends DefaultTableCellRenderer
{
    private final Set<Point> highlightedCells = new HashSet<Point>();

    void setHighlighted(int r, int c, boolean highlighted)
    {
        if (highlighted)
        {
            highlightedCells.add(new Point(r,c));
        }
        else
        {
            highlightedCells.remove(new Point(r,c));
        }
    }

    private boolean isHighlighted(int r, int c)
    {
        return highlightedCells.contains(new Point(r,c));
    }

    public Component getTableCellRendererComponent(JTable table, Object value,
        boolean isSelected, boolean hasFocus, int row, int column)
    {

        if (isHighlighted(row,  column))
        {
            setForeground(Color.BLACK);
            setBackground(Color.RED);
        }
        else
        {
            setForeground(Color.BLACK);
            setBackground(Color.WHITE);
        }
        return this;
    }
}

You can then create an instance of this renderer, and add or remove cells to be highlighted:

ColoringCellRenderer r = new ColoringCellRenderer();
// Assign renderer to table...
...

// Later, highlight cells:
r.setHighlighted(4,2,true);
r.setHighlighted(6,1,true);
r.setHighlighted(1,5,false);
...

If you want different colors for the cells, you could replace the Set with a Map that maps a particular Point (representing the row/column of the cell) to a Color object.