Jlist and Jbuttons resizing after Japplet runs

Vector vector = new Vector()

JButton add = new JButton("add");

JButton remove = new JButton("remove");

DefaultListModel model =new DefaultListModel();

JList firstList = new JList(vector);

Jlist selectedList = new Jlist(model);


JPanel rightPanel = new JPanel();

rightPanel.add(selectedList);

JPanel leftPanel = new JPanel();

leftPanel.add(firstList );

JPanel centerButtons = new JPanel(new GridLayout(2,1);

centerButtons.add(add);
centerButtons.add(remove);

add.addActionListener(new ButtonListener());
remove.addActionlistener(new RemoveButton());

setLayout(new BorderLayout());

add(rightPanel, BorderLayout.EAST);
add(leftPanel, BorderLayout.WEST);
add(centerButtons, BorderLayout.CENTER);

     private class ButtonListener implements ActionListener
      {
        public void actionPerformed(ActionEvent e) {


                model.addElement(firstList.getSelectedValue());
           
          

        }