ScrollBar is added from scrach but not in the middle of work - java swing frame

I don't know where the problem is, when the sample code is run alone and from scratch, the scrollbars are displayed correctly, but when we try to add them to a task area in the middle of a prepared frame, the text area disappears. The last solution I tried was this:

 createAndShowGUI() {
 //
 JTextArea textArea = new JTextArea(20, 20);
 JScrollPane scrollableTextArea = new JScrollPane(textArea);
 scrollableTextArea.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);
 frame.getContentPane().add(scrollableTextArea)
 //}

and for run it:

 javax.swing.SwingUtilities.invokeLater(new Runnable() {
        public void run() {
           createAndShowGUI();
       }
   });

and had the same problem, Can Anybody Help?

Edit: I have to correct the question

In a good example, I would use this Line:

frame.getContentPane().setLayout(new FlowLayout());

And in bad usage, I used this line:

frame.getContentPane().setLayout(null); //"null" cannot be replaced because the frame and its objects are moved

Is there a layout that does not move the previous objects of the frame and shows the scroll bar correctly?

I found the solution to the problem by selecting the appropriate layout:

frame1= new JFrame("farme1");
frame1.setBounds(100, 100, 200, 200);
frame1.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame1.setLayout(new BoxLayout(frame1.getContentPane(),BoxLayout.PAGE_AXIS) );//**key point**
frame1.setResizable(false);
JPanel pane = new JPanel(new GridBagLayout());
pane.setLayout(new GridBagLayout());
GridBagConstraints c = new GridBagConstraints();

and some other initialization for c.