Example Depot

JTable table = new JTable();

// Add data

// Create text field and add action
JTextField textField = new JTextField();
textField.setAction(new UpdateAnchorAction(table));

// Add selection listener to table
SelectionListener listener = new SelectionListener(table, textField);
table.getSelectionModel().addListSelectionListener(listener);
table.getColumnModel().getSelectionModel()
    .addListSelectionListener(listener);

// Add value changed listener to table
table.getModel().addTableModelListener(new MyTableModelListener(table, textField));

// Create a frame and add both components to the frame
JFrame frame = new JFrame();
frame.getContentPane().add(new JScrollPane(table), BorderLayout.CENTER);
frame.getContentPane().add(textField, BorderLayout.NORTH);
frame.pack();
frame.setVisible(true);

public class SelectionListener implements ListSelectionListener {
    JTable table;
    JTextField textField;

    // It is necessary to keep the table since it is not possible
    // to determine the table from the event's source
    SelectionListener(JTable table, JTextField textField) {
        this.table = table;
        this.textField = textField;
    }

    // Update the text field whenever the anchor cell changes
    public void valueChanged(ListSelectionEvent e) {
        int rowIndex = table.getSelectionModel().getAnchorSelectionIndex();
        int vColIndex = table.getColumnModel().getSelectionModel()
            .getAnchorSelectionIndex();

        // Get the value and set the text field
        textField.setText((String)table.getValueAt(rowIndex, vColIndex));
    }
}

public class MyTableModelListener implements TableModelListener {
    JTable table;
    JTextField textField;

    // It is necessary to keep the table since it is not possible
    // to determine the table from the event's source
    MyTableModelListener(JTable table, JTextField textField) {
        this.table = table;
        this.textField = textField;
    }

    // Update the text field whenever the value in the anchor cell changes
    public void tableChanged(TableModelEvent e) {
        // Get anchor cell location
        int rAnchor = table.getSelectionModel().getAnchorSelectionIndex();
        int vcAnchor = table.getColumnModel().getSelectionModel()
            .getAnchorSelectionIndex();

        // This method is defined in
        // Converting a Column Index Between the View and Model in a JTable Component
        int mcAnchor = toModel(table, vcAnchor);

        // Get affected rows and columns
        int firstRow = e.getFirstRow();
        int lastRow = e.getLastRow();
        int mColIndex = e.getColumn();

        if (firstRow != TableModelEvent.HEADER_ROW
                && rAnchor >= firstRow
                && rAnchor <= lastRow
                && (mColIndex == TableModelEvent.ALL_COLUMNS
                    || mColIndex == mcAnchor)) {
            // Set the text field with the new value
            textField.setText((String)table.getValueAt(rAnchor, vcAnchor));
        }
    }
}

public class UpdateAnchorAction extends AbstractAction {
    JTable table;
    UpdateAnchorAction(JTable table) {
        super("Set Anchor");
        this.table = table;
    }

    // Update the value in the anchor cell whenever the text field changes
    public void actionPerformed(ActionEvent evt) {
        JTextField textField = (JTextField)evt.getSource();

        // Get anchor cell location
        int rAnchor = table.getSelectionModel().getAnchorSelectionIndex();
        int vcAnchor = table.getColumnModel().getSelectionModel()
            .getAnchorSelectionIndex();

        table.setValueAt(textField.getText(), rAnchor, vcAnchor);
    }
}