title: JTable is not showing
body: <p>Can someone tell me what's wrong with this code?  It's not showing anything except the menu and I can't seem to figure out what is wrong.</p>
  
  <pre><code> public class ProfesorSelect extends JFrame {
      public ProfesorSelect(Profesor profesor){
          setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          JMenuBar menuBar = new JMenuBar();
          JMenu fileMenu = new JMenu("File");
          JMenuItem newItem = new JMenuItem("Logout");
          JMenuItem open = new JMenuItem("Exit");
          setLayout(new GridBagLayout());
          GridBagConstraints constraints = new GridBagConstraints();
          constraints.anchor = GridBagConstraints.CENTER;
          fileMenu.add(newItem);
          fileMenu.add(open);
          setName(profesor.toString() + " /Profesor");
          menuBar.add(fileMenu);
          JScrollPane panel = new JScrollPane();
          JScrollPane scrollPanel = new JScrollPane(JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED, JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
          for(Clasa clasa: Centralizator.getInstance().getClase()){
              JPanel panelClasa = new JPanel();
              panelClasa.setLayout(new BoxLayout(panelClasa,BoxLayout.Y_AXIS));
              JLabel numeClasa = new JLabel(clasa.getIdClasa());
              ArrayList&lt;String&gt; elevi = new ArrayList&lt;String&gt;();
              for (Elev elev : clasa.getElevi()){
                  elevi.add(elev.toString());
              }
              JScrollPane jScrollPane = new JScrollPane(new JList(elevi.toArray()));
              panelClasa.add(numeClasa);
              panelClasa.add(jScrollPane);
              scrollPanel.add(panelClasa);
          }
          add(scrollPanel);
  
          setJMenuBar(menuBar);
          pack();
          setVisible(true);
      }
  }
  </code></pre>