J Table - Single Cell Alignment

Question

Hello everyone,
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.util.Random;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.table.DefaultTableModel;
import javax.swing.table.TableCellRenderer;
import javax.swing.table.TableColumnModel;
public class RowColorTest
    private JTable table;
    public static void main(String[] args)
        new RowColorTest();
    public RowColorTest()
        javax.swing.SwingUtilities.invokeLater(new Runnable()
            public void run()
                createGUI();
    public void createGUI()
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        String[] columnNames = new String[4];
        columnNames[0] = "Name";
        columnNames[1] = "Age";
        columnNames[2] = "Value";
        columnNames[3] = "Extra";
        Object[][] data = new Object[20][4];
        Random r = new Random();
        for(int a=0; a < 4; a++)
            for(int i=0; i < 20; i++)
                if(i == 0 || i == 5 || i == 10 || i == 15)
                    data[i][a] = 23;
                else
                    data[i][a] = r.nextInt(50);
        DefaultTableModel model = new DefaultTableModel(data, columnNames);
        table = new JTable(model)
            public boolean isCellEditable(int rowIndex, int vColIndex)
                return false;
            public Class getColumnClass(int column)
                return getValueAt(0, column).getClass();
            public Component prepareRenderer(TableCellRenderer renderer, int row, int column)
                Component c = super.prepareRenderer(renderer, row, column);
                TableColumnModel tcm = table.getColumnModel();
                Object result = getValueAt(row, tcm.getColumnIndex("Value"));
                if(result instanceof Integer)
                    if(((Integer) result) == 23)
                        c.setBackground(new Color(0, 255, 153));
                        c.setForeground(Color.BLACK);
                        if(column == 0)
                                // I would like to do a CELL ALIGNMENT for this particular condition.
                                // setHorizontalAlignment() does not exist for the object c (Component).
                    else
                        c.setBackground(Color.WHITE);
                        c.setForeground(Color.BLACK);
                        if(column == 0)
                                // I would like to do a CELL ALIGNMENT for this particular condition.
                                // setHorizontalAlignment() does not exist for the object c (Component).
                if(table.isRowSelected(row))
                    c.setBackground(Color.BLUE);
                    c.setForeground(Color.WHITE);
                return c;
        JPanel panel = new JPanel();
        JScrollPane sp = new JScrollPane(table);
        panel.add(sp, BorderLayout.CENTER);
        frame.setContentPane(panel);
        frame.pack();
        frame.setVisible(true);
}Sorry for bringing this up again, but I am having a hard time trying to "align" a single "cell". In the code that I have provided, I tried to find a method from the Component object for setHorizontalAlignment() hoping to make this call:
c.setHorizontalAlignment(SwingConstants.RIGHT);
However, it does not exist. How would I go about setting the alignment for an individual cell? I've searched the forum for "cell alignment" and found some information about using a DefaultTableCellRenderer, but I'm not sure how to merge that with the existing code that I currently have.
In this thread: http://forums.sun.com/thread.jspa?forumID=57&threadID=659910 , camickr pointed out that I can use the row and column variables to find which cell to align, however once I've found the particular cell that I'd like to align, what do I do next? The component c does not have a method to set alignment in this scenario.
Thanks again,
Brianiak

Answer 1

You - the programmer - know that the component in question will be a label of some kind. The compiler, however, does not. As far as javac is concerned, the component could be, say, a 3D animation, in which case setHorizontalAlignement would be illegal.
In order to share our runtime knowledge with the compiler, we have to use some explicit casting:
(JLabel)c.setHorizontalAlignment(javax.swing.SwingConstants.CENTER);Note that this will lead to runtime errors if our component is not an instance of JLabel, so it's a good idea to surround the code with:
if (c instanceof JLabel){
}