--- a/src/main/java/de/uapcore/sudoku/ButtonPanel.java Sat Jul 25 15:56:48 2020 +0200 +++ b/src/main/java/de/uapcore/sudoku/ButtonPanel.java Mon Jul 27 10:56:17 2020 +0200 @@ -34,7 +34,7 @@ */ public final class ButtonPanel extends JPanel { - private JButton save, check, solve; + private final JButton save, check, solve; public ButtonPanel(ActionHandler l) { setLayout(new GridBagLayout());