GroupLayout, nie widać komponentów :(

public class DelayMainFrame extends JFrame{

	private JPanel mainPanel;
	
	
	
	public DelayMainFrame() {  //constructor
		
		Toolkit kit = Toolkit.getDefaultToolkit();
		Dimension screenDimension = kit.getScreenSize();
		setSize(screenDimension.width/2, screenDimension.height/2);
		setLocationByPlatform(true);
		//LayoutManager2 manager = new BasicSplitPaneUI.BasicVerticalLayoutManager();
		
		//Components creation
				
		JTextField signalNameTextField = new JTextField("<Put the signal name here>",20);
		JLabel signalNameTextFieldLabel = new JLabel("Signal name", SwingConstants.RIGHT);
		
		JTextField blockNameTextField = new JTextField("<Put the block name here>",20);
		JLabel blockNameTextFieldLabel = new JLabel("Block name", SwingConstants.RIGHT);
		
		JComboBox iaComboBox = new JComboBox();
		iaComboBox.setEditable(true);
		iaComboBox.addItem("IS");
		iaComboBox.addItem("IA");
		
		//adding components to the panel
		mainPanel = new JPanel();
        GroupLayout layout = new GroupLayout(mainPanel);
        mainPanel.setLayout(layout);
        layout.setAutoCreateGaps(true);
        layout.setAutoCreateContainerGaps(true);
        
        layout.setHorizontalGroup(layout.createSequentialGroup()
                .addGroup(layout.createParallelGroup(LEADING)   //s1
                    .addComponent(signalNameTextFieldLabel)     //p1
                    .addComponent(blockNameTextFieldLabel))     //p2
                .addGroup(layout.createParallelGroup(LEADING)          //s2
                    .addComponent(signalNameTextField)                 //p1
                    .addComponent(blockNameTextField))                 //p2
                .addComponent(iaComboBox)
                            );
        
        //layout.linkSize(SwingConstants.HORIZONTAL);
        
        layout.setVerticalGroup(layout.createSequentialGroup()
        		      .addGroup(layout.createParallelGroup(BASELINE)
        		           .addComponent(signalNameTextFieldLabel)
        		           .addComponent(signalNameTextField)
        		      )
        		      .addGroup(layout.createParallelGroup(BASELINE)
        		    	   .addComponent(signalNameTextFieldLabel)
           		           .addComponent(signalNameTextField)
           		           .addComponent(iaComboBox)
        		      )) ;    
         		     
	
        setTitle("Signal delay tool by DRZ");
        //pack();

		try {
		UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsClassicLookAndFeel");
		SwingUtilities.updateComponentTreeUI(DelayMainFrame.this);
		}
		
		catch (Exception e)
		{
			e.printStackTrace();
		}
		
		
	}  // end constructor

public class HelloWorld {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		//System.out.println("Hello World!");
		EventQueue.invokeLater(new Runnable() {
		
			public void run() {
				DelayMainFrame myFrame = new DelayMainFrame();
				myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
				myFrame.setVisible(true);
			}
		});
	}

}

add(mainPanel);