Keep focus on keyboard when checkbox is selected

I have a multiple-choice JavaSwing app that has checkboxes and next/previous buttons. I had it modified so focus is now on the Next button when it launches, allowing user to press Enter/Return to go to next screen.

The problem now is when user selects a checkbox, the Next button loses its keyboard focus and grey outline. Coder has added a hack so the button is regains focus and grey outline each time a checkbox is selected, but then the button blinks on each mouse-click! Some screens have 4 correct checkboxes, so button blinks 4 times.

I think this is unacceptable behaviour but he says,"Expected behavior is when you select any control its obvious it gains focus on that Element. You are saying to override Java Inbuilt Functionality which is not possible."

This just feels wrong. Is he right? Is there any source I can point him to that will allow him to keep focus on checkboxes on mouse-click, while keeping keyboard focus on buttons?

Many thanks in advance.