Maintaining JTable Cell Rendering After Cell Edit

In a JTable, implementing custom cell rendering and editing capabilities can enhance the user experience. However, it's crucial to ensure that the desired formatting is preserved even after editing operations.

The Issue

After setting up a custom cell renderer for formatting a "price" column, users encountered a discrepancy where the number format was lost upon cell editing. In such scenarios, the default value of the cell renderer might not be applied after the edit is committed.

The Solution

To maintain the custom rendering after cell edit, it's essential to utilize the proper event triggers and classes. When editing concludes, the JTable's editingStopped() method collects the new value via getCellEditorValue(). The model is then notified with setValueAt() and should subsequently call fireTableCellUpdated(). This comprehensive process invokes the renderer, which can be extended to handle special formatting needs.

Additional Considerations

For more intricate formatting requirements, it's recommended to consider utilizing an instance of the custom renderer as the editor component itself. This allows for greater control over the cell's appearance and behavior, ensuring consistent formatting even after cell modifications.

Example

The following code snippet provides an example implementation that demonstrates how to format currency values as numbers in JTable cells. The custom renderer (CurrencyRenderer) handles the currency formatting, while the custom editor (CurrencyEditor) allows users to edit the values while maintaining the formatting.

import java.awt.Component;
import java.awt.event.MouseEvent;
import java.text.NumberFormat;
import javax.swing.DefaultCellEditor;
import javax.swing.JTable;
import javax.swing.JTextField;
import javax.swing.table.DefaultTableCellRenderer;

// Custom cell renderer for currency formatting
public class CurrencyRenderer extends DefaultTableCellRenderer {

    private NumberFormat formatter;

    public CurrencyRenderer(NumberFormat formatter) {
        this.formatter = formatter;
        setHorizontalAlignment(JLabel.RIGHT);
    }

    @Override
    public void setValue(Object value) {
        setText((value == null) ? "" : formatter.format(value));
    }
}

// Custom cell editor for currency input, maintaining the formatting
public class CurrencyEditor extends DefaultCellEditor {

    private NumberFormat formatter;
    private JTextField textField;

    public CurrencyEditor(NumberFormat formatter) {
        super(new JTextField());
        this.formatter = formatter;
        textField = (JTextField) getComponent();
        textField.setHorizontalAlignment(JTextField.RIGHT);
        textField.setBorder(null);
    }

    @Override
    public Object getCellEditorValue() {
        try {
            return new Double(textField.getText());
        } catch (NumberFormatException e) {
            return Double.valueOf(0);
        }
    }

    @Override
    public Component getTableCellEditorComponent(JTable table,
            Object value, boolean isSelected, int row, int column) {
        textField.setText((value == null)
                ? "" : formatter.format((Double) value));
        return textField;
    }
}

By incorporating these techniques, developers can ensure that custom cell rendering and editing capabilities work seamlessly in JTable, providing a consistent and user-friendly data manipulation experience.