use these lines of code:

            Locale locale = new Locale( "fa" , "ir" );
            Locale.setDefault( locale );
            MyComponent.applyComponentOrientation( ComponentOrientation.getOrientation ( Locale.getDefault() ) );

simply use the following statement:
----
box.setComponentOrientation(ComponentOrientation.RIGHT_TO_LEFT);
---

It was my problem years ago, its fixed in 6th edition. in java 1.4 and above
you can get all components within jcombobox  and change the orientation of them
to RTL one by one.