java checkbox not showing

In my code i want to add three checkboxes but only the last one is shown and i dont know why :(

my windows

JCheckBox check_global = new JCheckBox("");
check_datum.setBounds(262, 65, 21, 21);
contentPane2.add(check_global);

JCheckBox check_mitarbeiter = new JCheckBox("");
check_datum.setBounds(237, 65, 21, 21);
contentPane2.add(check_mitarbeiter);

JCheckBox check_verrechenbarFix = new JCheckBox("");
check_datum.setBounds(237, 10, 21, 21);             
contentPane2.add(check_verrechenbarFix);