{"a",1,2},{"b",3,4}  -  ??

You don't need custom editor and KeyListener
(but if you want you'd better to use JFormattedTextField which
you may pass to a constructor of DefaultCellEditor).

You may create your own TableModel where you need to override
getColumnClass and your table will know what to do.

Your class back (different name) with custom table model.

import java.awt.Component;
import java.awt.Toolkit;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.ArrayList;
import java.util.List;

import javax.swing.DefaultCellEditor;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTable;
import javax.swing.JTextField;
import javax.swing.table.AbstractTableModel;
import javax.swing.table.TableColumnModel;
import javax.swing.table.TableModel;

public class NumericColumnTester extends JFrame {

    public NumericColumnTester() {                       
//        JTable table = new JTable(new Object[][] {
//                { "a", new Integer(1), "2" }, { "b", new Integer(3), "4" } },
//                new String[] { "Text", "Num 1", "Num 2" });
       
        String[]header = { "Text", "Num 1", "Num 2" };
        List data = new ArrayList();
        data.add(new Object[]{ "a", new Integer(1), "2" });
        data.add(new Object[]{ "b", new Integer(3), "4" });
        TableModel model = new TblModel(data, header);
        JTable table = new JTable(model);
        table.setRowSelectionAllowed(false);
        table.setSurrendersFocusOnKeystroke(true);

//        TableColumnModel cm = table.getColumnModel();
//        cm.getColumn(1).setCellEditor(new MyCellEditor());
//        cm.getColumn(2).setCellEditor(new MyCellEditor());

        JScrollPane scrollPane = new JScrollPane(table);
        getContentPane().add(scrollPane);
    }

    private class MyCellEditor extends DefaultCellEditor {

        private final JTextField    tf;

        public MyCellEditor() {
            super(new JTextField());
            tf = (JTextField) getComponent();
            tf.addKeyListener(new MyKeyListener());
            setClickCountToStart(1);
        }

        public Component getTableCellEditorComponent(JTable table,
                Object value, boolean isSelected, int row, int column) {
            tf.setText(value.toString());
            return tf;
        }

        public Object getCellEditorValue() {
            return tf.getText();
        }
    }

    class TblModel extends AbstractTableModel {

        private List        data;
        private String[]    header;

        public TblModel(List data, String[] header) {
            this.data = data;
            this.header = header;
        }

        public boolean isCellEditable(int rowIndex, int columnIndex) {
            return columnIndex == 1;
        }

        public int getColumnCount() {
            return header == null ? 0 : header.length;
        }

        public int getRowCount() {
            return data == null ? 0 : data.size();
        }

        public Object getValueAt(int rowIndex, int columnIndex) {
            Object[] row = (Object[]) data.get(rowIndex);
            return row[columnIndex];
        }

        public Class getColumnClass(int columnIndex) {
            if (data == null) {
                return Object.class;
            }
            Object[] row = (Object[]) data.get(0);
            return row[columnIndex] == null ? Object.class :
row[columnIndex].getClass();
        }

        public String getColumnName(int column) {
            return header[column];
        }

        public void setValueAt(Object aValue, int rowIndex, int columnIndex) {
            Object[] row = (Object[]) data.get(rowIndex);
            row[columnIndex] = aValue;
            super.fireTableCellUpdated(rowIndex, columnIndex);
        }

    }

    private class MyKeyListener implements KeyListener {

        public void keyPressed(KeyEvent e) {
        }

        public void keyReleased(KeyEvent e) {
        }

        public void keyTyped(KeyEvent e) {
            if (!Character.isDigit(e.getKeyChar())) {
                Toolkit.getDefaultToolkit().beep();
                e.consume();
            }
        }
    }

    public static void main(String[] args) {
        JFrame frame = new NumericColumnTester();
        frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}