Swing JComboBox within a JTable

import java.awt.Component;
import java.awt.event.ActionEvent;
import java.awt.event.InputEvent;
import java.awt.event.KeyEvent;
import javax.swing.Action;
import javax.swing.BorderFactory;
import javax.swing.DefaultCellEditor;
import javax.swing.InputMap;
import javax.swing.JComboBox;
import javax.swing.JComponent;
import javax.swing.JTable;
import javax.swing.KeyStroke;
import javax.swing.table.TableCellEditor;

public class Main extends javax.swing.JFrame {

    public Main() {      
        initComponents();
        startEditingWithAltDown(jTable1);
        startEditingAction(jTable1);
        jTable1.changeSelection(0, 0, false, false);
    }
    
    private TableCellEditor createComboBoxCellEditor() {
        JComboBox comboBox = new JComboBox(new Object[]{"A", "B"});
        comboBox.setBorder(BorderFactory.createEmptyBorder());         
        return new DefaultCellEditor(comboBox);
    }    
    
    private void startEditingWithAltDown(JTable table) {
        KeyStroke keystroke = KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, InputEvent.ALT_MASK);
        InputMap inputMap = table.getInputMap(JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT);
        inputMap.put(keystroke, "startEditing");
    }  
    
    private void startEditingAction(final JTable table) {
        Action action = new javax.swing.AbstractAction() {
            public void actionPerformed(ActionEvent e) {
                int row = table.getSelectedRow();
                int column = table.getSelectedColumn();
                table.editCellAt(row, column);
                TableCellEditor editor = table.getCellEditor();
                if (editor == null) {
                    return;
                }
                Object v = table.getValueAt(row, column);
                if (v == null) {
                    v = "";
                }
                Component editorComponent = editor.getTableCellEditorComponent(table, v, true, row, column);             
                if (editorComponent instanceof JComboBox) {
                    JComboBox ec = ((JComboBox)editorComponent);
                    if (!ec.isPopupVisible()) {                           
                        ec.requestFocus();
                        ec.showPopup();
                    }                    
                } 
            }
        };        
        table.getActionMap().put("startEditing", action);
    }

    @SuppressWarnings("unchecked")
    // 
    private void initComponents() {

        jScrollPane1 = new javax.swing.JScrollPane();
        jTable1 = new javax.swing.JTable();
        jPanel1 = new javax.swing.JPanel();
        jLabel1 = new javax.swing.JLabel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        jTable1.setModel(new javax.swing.table.DefaultTableModel(
            new Object [][] {
                {null, null},
                {null, null}
            },
            new String [] {
                "Title 1", "Title 2"
            }
        ));
        jScrollPane1.setViewportView(jTable1);
        jTable1.getColumnModel().getColumn(0).setCellEditor(createComboBoxCellEditor());
        jTable1.getColumnModel().getColumn(1).setCellEditor(createComboBoxCellEditor());

        getContentPane().add(jScrollPane1, java.awt.BorderLayout.CENTER);

        jPanel1.setLayout(new java.awt.BorderLayout());

        jLabel1.setText("ComboBox showPopup: F2 or Alt+Down");
        jPanel1.add(jLabel1, java.awt.BorderLayout.CENTER);

        getContentPane().add(jPanel1, java.awt.BorderLayout.PAGE_START);

        pack();
    }// 

    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new Main().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify
    private javax.swing.JLabel jLabel1;
    private javax.swing.JPanel jPanel1;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JTable jTable1;
    // End of variables declaration

}