JTable里的JComboBox在按空格键时不能显示下拉框

[zaghost]

通常的JComboBox在获得焦点时按空格键会显示下拉框，
但是JTable里的JComboBox，按空格键没有反应
这是为什么
有没有办法实现JTable里的JComboBox也能在按空格键会显示下拉框

附实例代码

public class T1 extends JComboBox implements TableCellRenderer {
	public T1() {
		setBorder(BorderFactory.createEmptyBorder());
		
		addActionListener(new ActionListener(){

			@Override
			public void actionPerformed(ActionEvent e) {
				// TODO 自動生成されたメソッド・スタブ
				System.out.println("gggg");
			}
			
		});
		
	}

	public static void main(String[] args) {

		JFrame f = new JFrame();
		
//		try {
//			UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
//		} catch (Exception e) {
//			e.printStackTrace();
//		}

		JComboBox comboBox = new JComboBox();
		comboBox.setBorder(BorderFactory.createEmptyBorder());
		comboBox.addItem("Item-1");
		comboBox.addItem("Item-2");
		comboBox.addItem("Item-3");
		comboBox.addItem("Item-4");
//		comboBox.addItem("Item-5");
		comboBox.setFocusable(true);
		
		DefaultCellEditor editor = new DefaultCellEditor(comboBox);
		

		JTable table = new JTable(5, 5);
		table.getColumnModel().getColumn(0).setCellRenderer(new T1());
		table.getColumnModel().getColumn(0).setCellEditor(editor);

		JScrollPane sp = new JScrollPane(table);
		
		f.getContentPane().add(sp, BorderLayout.CENTER);
		
		JComboBox cmb1 = new JComboBox();
		cmb1.setBorder(BorderFactory.createEmptyBorder());
		cmb1.addItem("Item-1");
		cmb1.addItem("Item-2");
		cmb1.addItem("Item-3");
		cmb1.addItem("Item-4");
		cmb1.addItem("Item-5");
//		cmb1.setFocusable(true);
		f.getContentPane().add(cmb1, BorderLayout.SOUTH);
		
		JComboBox cmb2 = new JComboBox();
		cmb2.setBorder(BorderFactory.createEmptyBorder());
		cmb2.addItem("Item-1");
		cmb2.addItem("Item-2");
		cmb2.addItem("Item-3");
		cmb2.addItem("Item-4");
		cmb2.addItem("Item-5");
		cmb2.setFocusable(true);
		f.getContentPane().add(cmb2, BorderLayout.NORTH);
		
		
		f.pack();
		f.setLocationRelativeTo(null);
		f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		f.setVisible(true);
	}

	public Component getTableCellRendererComponent(JTable table, Object value, boolean isSelected, boolean hasFocus,
			int row, int column) {
		this.removeAllItems();
		this.addItem(value);

		return this;
	}
}