Editing cell restrictions of a column in a JTable / TableModel

Question

I am looking to modify the way cell input is handled in my JTable. Currently I am using a DefaultTableModel as seen below.

 DefaultTableModel model = new DefaultTableModel() {

                @Override
                public boolean isCellEditable(int row, int col) {
                    return col == 1 || col == 2 || col == 6;
                }

                @Override
                public Class getColumnClass(int col) {
                    if (col == 6) {
                        return Integer.class;
                    } else {
                        return String.class;
                    }
                }

            };

With this code column 6 forces the user to input an Integer. I would like to take this further by not allowing the number to be outside of a range (e.g. 1-100) and also for the field to never be empty (The column will have data in it prior to user interaction). I have read the docummentation but cannot seem to find anything that manages the behaviour of column types. Thanks!

Answer 1

You would need to create a custom editor.

The following example demonstrates and editor that forces the data to be 5 characters:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
import javax.swing.table.*;

public class TableFiveCharacterEditor extends DefaultCellEditor
{
    private long lastTime = System.currentTimeMillis();

    public TableFiveCharacterEditor()
    {
        super( new JTextField() );
    }

    public boolean stopCellEditing()
    {
        JTable table = (JTable)getComponent().getParent();

        try
        {
            String editingValue = (String)getCellEditorValue();

            if(editingValue.length() != 5)
            {
                JTextField textField = (JTextField)getComponent();
                textField.setBorder(new LineBorder(Color.red));
                textField.selectAll();
                textField.requestFocusInWindow();

                JOptionPane.showMessageDialog(
                    table,
                    "Please enter string with 5 letters.",
                    "Alert!",JOptionPane.ERROR_MESSAGE);
                return false;
            }
        }
        catch(ClassCastException exception)
        {
            return false;
        }

        return super.stopCellEditing();
    }

    public Component getTableCellEditorComponent(
        JTable table, Object value, boolean isSelected, int row, int column)
    {
        Component c = super.getTableCellEditorComponent(
            table, value, isSelected, row, column);
        ((JComponent)c).setBorder(new LineBorder(Color.black));

        return c;
    }

    private static void createAndShowUI()
    {
        JTable table = new JTable(5, 5);
        table.setPreferredScrollableViewportSize(table.getPreferredSize());
        JScrollPane scrollPane = new JScrollPane(table);

        //  Use a custom editor

        TableCellEditor fce = new TableFiveCharacterEditor();
        table.setDefaultEditor(Object.class, fce);

        JFrame frame = new JFrame("Table Five Character Editor");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add( scrollPane );
        frame.pack();
        frame.setLocationByPlatform( true );
        frame.setVisible( true );
    }

    public static void main(String[] args)
    {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                createAndShowUI();
            }
        });
    }
}

You would need to modify the editor to make sure:

1. the data is an Integer by using the Integer.parseInt(...) method
2. that the Integer value is in your desired range

Edit:

how can I apply this to influence one column rather than the entire table.

You can add the editor to the TableColumn:

table.getColumnModel().getColumn(...).setCellEditor(...);

Answer 2

Overriding the behaviour of the DefaultCellEditor achieves the desired outcome.

            DefaultCellEditor editor = new DefaultCellEditor(new JTextField()) {
                @Override
                public boolean stopCellEditing() {
                    JTable table = (JTable) getComponent().getParent();
                    try {
                        String value = (String) getCellEditorValue();
                        if (Integer.parseInt(value) < 1) {
                            JTextField textField = (JTextField) getComponent();
                            textField.setBorder(new LineBorder(Color.red));
                            textField.selectAll();
                            textField.requestFocusInWindow();
                            return false;
                        }
                    } catch (NumberFormatException ex) {
                        return false;
                    }
                    return super.stopCellEditing();
                }
            };

Then added to the desired column of the table.

table.getColumnModel().getColumn(6).setCellEditor(editor);

Edit: The behaviour inside the if statement will not occur if a NumberFormatException is thrown, you may want to put the same lines of code within the catch.