Java Swing - 如何在JDialog中删除并将项目添加到JList

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;

import javax.swing.AbstractAction;
import javax.swing.DefaultListModel;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;

public class Main {
  static int N = 12;
  JDialog dlg = new JDialog();
  DefaultListModel model = new DefaultListModel();
  JList list = new JList(model);
  JScrollPane sp = new JScrollPane(list);
  int count;
  public Main() {
    list.setSelectionMode(javax.swing.ListSelectionModel.SINGLE_SELECTION);
    JPanel panel = new JPanel();
    panel.add(new JButton(new AbstractAction("Add") {
      @Override
      public void actionPerformed(ActionEvent e) {
        append();
        if (count <= N) {
          list.setVisibleRowCount(count);
          dlg.pack();
        }
      }
    }));
    panel.add(new JButton(new AbstractAction("Remove") {
      @Override
      public void actionPerformed(ActionEvent e) {
        int itemNo = list.getSelectedIndex();
        if (itemNo > -1) {
          removeActionPerformed(e, itemNo);
        }
      }
    }));
    for (int i = 0; i < N - 2; i++) {
      this.append();
    }
    list.setVisibleRowCount(N - 2);
    dlg.add(sp, BorderLayout.CENTER);
    dlg.add(panel, BorderLayout.SOUTH);
    dlg.pack();
    dlg.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
    dlg.setVisible(true);
  }
  private void removeActionPerformed(ActionEvent e, int itemNo) {
    model = (DefaultListModel) list.getModel();
    if (model.size() > 0) {
      if (itemNo > -1) {
        model.remove(itemNo);
      }
    }
  }
  private void append() {
    model.addElement("String " + String.valueOf(++count));
    list.ensureIndexIsVisible(count - 1);
  }
  public static void main(String[] a_args) {
    Main pd = new Main();
  }
}