Refreshing a set of JPanels

Question

Hello there,
I have an issue with refreshing and replacing my JPanel colors. As you can see, the format is GridLayout with the size of the grid changing based on what file they open. My issue is that when a second file is opened, it merely adds those JPanels to the end of the previously loaded set of JPanels. I've tried refresh() and repaint() but to no avail. Maybe I placed them in the wrong place, not sure. Thanks in advance.
          if (actionCommand.equals("Open..."))
               JFileChooser fileChooser = new JFileChooser();
               fileChooser.setDialogTitle("Choose a file");
               this.getContentPane().add(fileChooser);
               fileChooser.setVisible(true);
               int result = fileChooser.showOpenDialog(this);
               File file = fileChooser.getSelectedFile();
               GridMap gm = new GridMap();
               gm.read(file);
               int row = gm.getRow();
               int col = gm.getColumn();
               setLayout(new GridLayout(row,col));
               for (int i = 0; i < row; i++)
                    for (int j = 0; j < col; j++)
                         JLabel color = new JLabel();
                         color.setOpaque(true);
                         if (gm.getGrid(i,j) == 'O')
                              color.setBackground(Color.GREEN);
                         else if (gm.getGrid(i,j) == 'F')
                              color.setBackground(Color.RED);
                         else if (gm.getGrid(i,j) == 'H')
                              color.setBackground(Color.BLACK);
                         add(color);
          }

Answer 1

something along these lines
import java.awt.*;
import java.awt.event.*;
import java.io.File;
import javax.swing.*;
public class MainFrame2
  private static final String EXIT = "Exit";
  private static final String OPEN = "Open...";
  private static final String START = "Start";
  private JPanel mainPanel = new JPanel();
  private JPanel gridPanel = new JPanel();
  public MainFrame2()
    mainPanel.setPreferredSize(new Dimension(300, 300));
    mainPanel.setLayout(new BorderLayout());
    mainPanel.add(gridPanel, BorderLayout.CENTER);
  public JComponent getPanel()
    return mainPanel;
  public JMenuBar createMenu()
    JMenu sim = new JMenu("Simulator");
    MenuListener menuListener = new MenuListener();
    JMenuItem m = new JMenuItem(OPEN);
    m.addActionListener(menuListener);
    sim.add(m);
    m = new JMenuItem(START);
    m.addActionListener(menuListener);
    sim.add(m);
    sim.addSeparator();
    m = new JMenuItem(EXIT);
    m.addActionListener(menuListener);
    sim.add(m);
    JMenuBar mBar = new JMenuBar();
    mBar.add(sim);
    return mBar;
  private class MenuListener implements ActionListener
    public void actionPerformed(ActionEvent e)
      String actionCommand = e.getActionCommand();
      if (actionCommand.equals(OPEN))
        JFileChooser fileChooser = new JFileChooser();
        fileChooser.setDialogTitle("Choose a file");
        //mainPanel.add(fileChooser);
        fileChooser.setVisible(true);
        int result = fileChooser.showOpenDialog(mainPanel);
        if (result == JFileChooser.APPROVE_OPTION)
          File file = fileChooser.getSelectedFile();
          GridMap gm = new GridMap();
          gm.read(file);
          int row = gm.getRow();
          int col = gm.getColumn();
          gridPanel.setLayout(new GridLayout(row, col));
          gridPanel.removeAll();
          for (int i = 0; i < row; i++)
            for (int j = 0; j < col; j++)
              JLabel color = new JLabel();
              color.setOpaque(true);
              if (gm.getGrid(i, j) == 'O')
                color.setBackground(Color.GREEN);
              else if (gm.getGrid(i, j) == 'F')
                color.setBackground(Color.RED);
              else if (gm.getGrid(i, j) == 'H')
                color.setBackground(Color.BLACK);
              gridPanel.add(color);
      else if (actionCommand.equals(START))
        // setVisible(true);
      else if (actionCommand.equals(EXIT))
        Window window = SwingUtilities.getWindowAncestor(mainPanel);
        window.dispose();
  private static void createAndShowGUI()
    MainFrame2 frame2 = new MainFrame2();
    JFrame frame = new JFrame("Fire Saving Simulator");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().add(frame2.getPanel());
    frame.setJMenuBar(frame2.createMenu());
    frame.pack();
    frame.setResizable(false);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  public static void main(String[] args)
    javax.swing.SwingUtilities.invokeLater(new Runnable()
      public void run()
        createAndShowGUI();
}