Question

I just started to learn swing by myself, I’m little bit confused why my event does not work here:

1.I’m trying to delete everything from my panel if the user click menu bar -> load but it force me to change the panel to final because i’m using it inside the event!

2.I have defined new panel in my event and defined two more container to add to that panel and then add it to the main frame but it seems nothing happening!

Please help me if you can find out what is wrong.
Sorry in advance for messy code.
I appreciate any hints.

public class SimpleBorder {

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                myFrame frame = new myFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setVisible(true); 
            }
        });
    }
}

class MyFrame extends JFrame {

    public MyFrame()
    {

        setSize(500,500);   
        JPanel panel = new JPanel();

        panel.setLayout(null);
        JLabel label = new JLabel("my name is bernard...");
        Color myColor = new Color(10, 150, 80);
        panel.setBackground(myColor);
        label.setFont(new Font("Serif", Font.PLAIN, 25));
        Dimension size = label.getPreferredSize();
        Insets insets = label.getInsets();
        label.setBounds(85+insets.left, 120+insets.top , size.width, size.height);

        panel.add(label);

        JMenuBar menu = new JMenuBar();
        setJMenuBar(menu);


        JMenu col = new JMenu("Collection");
        menu.add(col);

        JMenu help = new JMenu("Help");
        menu.add(help);

        Action loadAction = new AbstractAction("Load")//menu item exit goes here
        {
            private static final long serialVersionUID = 1L;
            public void actionPerformed(ActionEvent event)
            {
                JTextArea text = new JTextArea(10, 40);
                JScrollPane scrol1 = new JScrollPane(text);
                String[] items = {"A", "B", "C", "D"};          
                JList list = new JList(items);
                JScrollPane scrol2 = new JScrollPane(list);
                JPanel panel2 = new JPanel(new BorderLayout());
                panel2 = new JPanel(new GridLayout(1, 2 ));
                panel2.add(scrol1,BorderLayout.WEST);
                panel2.add(scrol2,BorderLayout.EAST);
                add(panel2);        
            }
        };
        JMenuItem load = new JMenuItem(loadAction);
        col.add(load);
        add(panel);

    }

}

Answer 1

Call revalidate()/repaint() on your JFrame instance after adding the new panel:

JPanel panel2 = new JPanel(new BorderLayout());
// panel2 = new JPanel(new GridLayout(1, 2 ));//why this it will overwrite the above layout
panel2.add(scrol1,BorderLayout.WEST);
panel2.add(scrol2,BorderLayout.EAST);
add(panel2);  
revalidate();
repaint();

Also call pack() on you JFrame instance so all components are spaced by the layoutmanager. As said in a comment dont extend the JFrame class, create a variable of the frame and initiate all that you need on the frames instance, and dont set a layout to null, unless you love hard work 😛

Alternatively as mentioned by mKorbel, a CardLayout may be more what you want, it will allow you to use a single JPanel and switch between others/new ones:

JPanel cards;
final static String BUTTONPANEL = "Card with JButtons";
final static String TEXTPANEL = "Card with JTextField";

//Where the components controlled by the CardLayout are initialized:
//Create the "cards".
JPanel card1 = new JPanel();
...
JPanel card2 = new JPanel();
...

//Create the panel that contains the "cards".
cards = new JPanel(new CardLayout());
cards.add(card1, BUTTONPANEL);
cards.add(card2, TEXTPANEL);

//add card panel to frame
frame.add(cards);

//swap cards
CardLayout cl = (CardLayout)(cards.getLayout());//get layout of cards from card panel
cl.show(cards, TEXTPANEL);//show another card