Proper way to write a Renderer?

Question

Why does this JTable show up with all three rows showing "Here". I only wanted the first one to. What is the proper way to write a JLabel renderer so that when I update a cell, it won't update the rest of the cells?
import javax.swing.*;
import javax.swing.table.DefaultTableModel;
import javax.swing.table.TableCellRenderer;
import java.awt.*;
public class post extends JFrame {
private class JLabelRenderer extends JLabel implements TableCellRenderer {
public Component getTableCellRendererComponent(JTable table, Object value,
boolean isSelected, boolean hasFocus,
int row, int column) {
if (value instanceof String) this.setText((String) value);
return this;
private post() {
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setSize(300, 300);
final DefaultTableModel model = new DefaultTableModel(3, 1);
JTable jtable = new JTable(model);
jtable.getColumnModel().getColumn(0).setCellRenderer(new JLabelRenderer());
jtable.setRowHeight(20);
JScrollPane pane = new JScrollPane(jtable);
this.getContentPane().add(pane);
this.show();
// Just update the FIRST cell of the FIRST ROW.
jtable.setValueAt("Here", 0, 0);
public static void main(String[] args) {
post blah = new post();

Answer 1

Every cell shares the same renderer. So once you set a property of the renderer, all cells use that property.
You use the setText() method to set the label to "Here", but it is never reset to another value. Try:
if (value instanceof String) this.setText((String) value);
else this.setText("");
However, here is a better example of how to write a Renderer:
import java.awt.*;
import javax.swing.*;
import javax.swing.table.*;
class HexCellRenderer extends DefaultTableCellRenderer
     private static final Color hexBackground = Color.cyan;
     public Component getTableCellRendererComponent(JTable table,
                                    Object value,
                                    boolean isSelected,
                                    boolean hasFocus,
                                    int row,
                                    int column)
          super.getTableCellRendererComponent(table, value, isSelected, hasFocus, row, column);
          setBackground( hexBackground );
          setHorizontalAlignment( CENTER );
          return this;
}You should extend DefaultTableCellRenderer, which extends JLabel. The DefaultTableCellRenderer already sets the text of the label so your don't have to worry about it.