Java Swing：无法显示我的JPanel的多个实例

Question

I'm making a GUI and having trouble with a JPanel.

First of all here is my JPanel:

public class ExperimentPanel extends JPanel{

private static File file1,file2=null;

private static DefaultListModel model = new DefaultListModel();
private static JList list = new JList(model);

private static JPanel mainpanel = new JPanel();
private static JPanel leftpanel = new JPanel();
private static JPanel rightpanel = new JPanel();
private static JPanel twoFiles = new SelectTwoFiles();
private static JPanel folderOrFile = new SelectFolderOrFile();
private static JPanel foldersOrFiles = new SelectTwoFoldersOrFiles();

public ExperimentPanel(int selectID){

    this.setBorder(new EmptyBorder(10, 10, 10, 10));

    if(selectID==Constants.SelectTwoFiles){
    this.add(twoFiles, BorderLayout.NORTH);
    }
    else if(selectID==Constants.SelectFolderOrFile){
    this.add(folderOrFile, BorderLayout.NORTH);
    }
    else if(selectID==Constants.SelectTwoFoldersOrFiles){
    this.add(foldersOrFiles,BorderLayout.NORTH);
    }

    JButton remove =new JButton("Remove Method");
    JButton add = new JButton("Add Method");
    JButton save = new JButton("Save list");
    JButton load = new JButton("Load list");

    leftpanel.add(new JScrollPane(list));
    Box listOptions = Box.createVerticalBox();
    listOptions.add(add);
    listOptions.add(remove);
    listOptions.add(save);
    listOptions.add(load);

    rightpanel.add(listOptions);

    Box mainBox = Box.createHorizontalBox();

    mainBox.add(leftpanel);
    mainBox.add(rightpanel);
    //mainBox.add(leftleft);

    this.add(mainBox, BorderLayout.CENTER);

    //start jobs
    JButton start = new JButton("Launch experiment");
    this.add(start,BorderLayout.PAGE_END);

    start.addActionListener(launch);
    add.addActionListener(adding);
    remove.addActionListener(delete);
}

public static ActionListener launch = new ActionListener(){
      public void actionPerformed(ActionEvent event){
          //check the files
          if((file1==null)||(file2==null)){
              JOptionPane.showMessageDialog(null,
                        "A graph file is missing",
                        "Wrong files",
                        JOptionPane.ERROR_MESSAGE);
          }

            //checks the list
      }
};

public static ActionListener delete = new ActionListener() {
      public void actionPerformed(ActionEvent event) {
        ListSelectionModel selmodel = list.getSelectionModel();
        int index = selmodel.getMinSelectionIndex();
        if (index >= 0)
          model.remove(index);
      }
 };

public static ActionListener adding = new ActionListener(){
      public void actionPerformed(ActionEvent event){

          JComboBox combo = new JComboBox();
          final JPanel cards = new JPanel(new CardLayout());

          JPanel form = new JPanel();
          JPanel methode1 = new JPanel();
          methode1.add(new JLabel("meth1"));
          methode1.setBackground(Color.BLUE);
          methode1.setName("meth1");
          JPanel methode2 = new JPanel();
          methode2.add(new JLabel("meth2"));
          methode2.setBackground(Color.GREEN);
          methode1.setName("meth2");
          combo.addItem("meth1");

          combo.addItem("meth2");
          cards.add(methode1,"meth1");
          cards.add(methode2,"meth2");

          JPanel control = new JPanel();
          combo.addActionListener(new ActionListener() {

                public void actionPerformed(ActionEvent e) {
                    JComboBox jcb = (JComboBox) e.getSource();

                    CardLayout cl = (CardLayout) cards.getLayout();
                    cl.show(cards, jcb.getSelectedItem().toString());
                }
            });
            control.add(combo);

            form.add(cards, BorderLayout.CENTER);
            form.add(control, BorderLayout.SOUTH);

            JOptionPane.showMessageDialog(null,form,"Select a method",JOptionPane.PLAIN_MESSAGE);               
      }
};
}

The problem is that if i create several instances of that panel they won't show like intended.

I tried creating 2 simple JFrames in my main with a new ExperimentPanel for each so the problem is not from the caller.

It works well with one JFrame calling one experiementPanel.

here is the display for one and 2 calls:

http://imgur.com/a/4DHJn

And how i call them:

    JFrame test = new JFrame();
    test.add(new ExperimentPanel(3));
    Dimension dim = Toolkit.getDefaultToolkit().getScreenSize();
    test.setLocation(dim.width/3 - test.getWidth()/3, dim.height/3 - test.getHeight()/3);
    test.setSize(550,300);
    test.setVisible(true);

    JFrame test2 = new JFrame();
    test2.add(new ExperimentPanel(3));
    test2.setLocation(dim.width/3 - test.getWidth()/3, dim.height/3 - test.getHeight()/3);
    test2.setSize(550,300);
    test2.setVisible(true);

Answer 1

You create a Panel class ExperimentPanel which itself consists of several components which are stored in class fields of ExperimentPanel .

Since you declare these class fields as static there is only one instance of them. When you instantiate several ExperimentPanel objects they all want to share these fields, which leads to the effects you have seen.

Therefore remove the static modifier from these fields:

public class ExperimentPanel extends JPanel{
    private File file1,file2=null;
    private DefaultListModel model = new DefaultListModel();
    private JList list = new JList(model);
    private JPanel mainpanel = new JPanel();
    private JPanel leftpanel = new JPanel();
    ...