Java Swing - 如何创建JOptionPane以从列表中选择

import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;

import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextField;
import javax.swing.ListSelectionModel;

public class Main extends JPanel {
  JTextField fileField = new JTextField(20);
  JButton showDialog = new JButton(new ShowDialogAction("Show Dialog",
      KeyEvent.VK_D, this));

  public Main() {
    fileField.setEditable(false);
    fileField.setFocusable(false);
    add(new JLabel("File Selected:"));
    add(fileField);
    add(showDialog);
  }

  public void setFileFieldText(String text) {
    fileField.setText(text);
  }

  public static void main(String[] args) {
    Main mainPanel = new Main();
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().add(mainPanel);
    frame.pack();
    frame.setVisible(true);
  }
}

class ShowDialogAction extends AbstractAction {
  private Main swingFoo;

  public ShowDialogAction(String name, int mnemonic, Main swingFoo) {
    super(name);
    putValue(MNEMONIC_KEY, mnemonic);
    this.swingFoo = swingFoo;
  }

  @Override
  public void actionPerformed(ActionEvent e) {
    MyPanel patientPicker = new MyPanel();
    int result = JOptionPane.showConfirmDialog(swingFoo, patientPicker,
        "Select Something", JOptionPane.OK_CANCEL_OPTION);
    if (result == JOptionPane.OK_OPTION) {
      swingFoo.setFileFieldText(patientPicker.getSelectedItem());
    }
    patientPicker.setVisible(true);
  }
}

class MyPanel extends JPanel {
  private static final String[] ITEMS = { "Sunday", "Monday", "Tuesday",
      "Wednesday", "Thursday", "Friday" };
  private JList<String> selectionList = new JList<>(ITEMS);

  public MyPanel() {
    add(new JScrollPane(selectionList));
    selectionList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
  }

  public String getSelectedItem() {
    return selectionList.getSelectedValue();
  }

}