private void createGUI() {

        if(panel != null) {
            panel.removeAll();
            panel.revalidate();
            panel.repaint();
        }

        setTitle("Persoon aanmaken");
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        setSize(500, 300);

        panel = new JPanel();

        naam = new JTextField(10);
        bsn = new JTextField(9);

        persoonAanmaken = new JButton("Nieuw Persoon");
        persoonAanmaken.addActionListener(this);

        panel.add(new JLabel("Naam"));
        panel.add(naam);
        panel.add(new JLabel("BSN"));
        panel.add(bsn);
        panel.add(persoonAanmaken);
        panel.add(new JLabel("Alle personen"));

        overzicht = new JTextArea(10, 20);
        overzicht.setEditable(false);

        personenList = new JComboBox();
        personenList.addItem("");
        for (Persoon p : app.getPersonen()) {
            personenList.addItem(p);
        }


        personenList.addItemListener(new ItemListener(){

            Persoon selectedPerson;

            @Override
            public void itemStateChanged(ItemEvent event) {
                //To change body of implemented methods use File | Settings | File Templates.
                if (event.getStateChange() == ItemEvent.SELECTED) {
                    Object item = event.getItem();
                    // do something with object
                    if(item instanceof Persoon) {
                        this.selectedPerson = (Persoon) item;
                        System.out.println("De volgende persoon is geselecteerd " + selectedPerson);
                        setOverzicht(selectedPerson);
                    } else {
                        System.out.println("null");
                        this.selectedPerson = null;
                    }
                }
            }
        });



        panel.add(personenList);

        panel.add(overzicht);

        this.setContentPane(panel);

        setVisible(true);

    }