GridBagLayout - Kan ikke få det vist

Jeg har problemer med at få tilføjet et GridBagLayout til et JPanel og vist det på skærmen, min klasse nedarver fra JPanel.

Min kode ser sådan ud:

    JPanel left, right, leftUp, leftDown;
    GridBagLayout leftUpLayout;
    GridBagConstraints leftUpLayoutContraints;
   
    public Constructor(){
   
        this.setLayout(new GridLayout(1,2));
       
        left = new JPanel(new GridLayout(2,1));
       
        leftDown = new JPanel();
        leftUp = new JPanel(leftUpLayout);

        left.add(leftUp);
        left.add(leftDown);
       
        leftUpLayout = new GridBagLayout();
        leftUpLayoutContraints = new GridBagConstraints();
        // Add Terminal TextField
        leftUpLayoutContraints.gridx = 0;
        leftUpLayoutContraints.gridy = 0;
        leftUpLayoutContraints.gridwidth = 3;
        leftUpLayoutContraints.gridheight = 1;
        leftUpLayoutContraints.fill = GridBagConstraints.HORIZONTAL;
        JTextField terminals = new JTextField("Terminals Found");
        leftUpLayout.setConstraints(terminals, leftUpLayoutContraints);
        leftUp.add(terminals);     
       
        right = new JPanel();
     
        this.add(left);
        this.add(right);
       
    }