问为什么即使包括了进口，也没有找到一些方法？

EN

import java.awt.*;
import java.io.*;
import java.util.prefs.*;

import javax.swing.*;
import javax.swing.filechooser.*;

/** A program to test preference settings. The program remembers the frame position, size, and title. **/
public class PreferencesTest {
    public static void main(String[] args) {
        EventQueue.invokeLater(() -> {
            PreferencesFrame frame = new PreferencesFrame();
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setVisible(true);
        });
    }
}

/** A frame that restores position and size from user preferences and updates the preferences upon exit. **/
class PreferencesFrame extends Frame {
    private static final int DEFAULT_WIDTH = 300;
    private static final int DEFAULT_HEIGHT = 200;
    private Preferences root = Preferences.userRoot();
    private Preferences node = root.node("/com/horstmann/corejava");

    public PreferencesFrame() {

        // Get position, size, and title from preferences.
        int left = node.getInt("left", 0);
        int top = node.getInt("top", 0);
        int width = node.getInt("width", DEFAULT_WIDTH);
        int height = node.getInt("height", DEFAULT_HEIGHT);
        setBounds(left, top, width, height);

        // If no title was given, ask the user.
        String title = node.get("title", "");
        if (title.equals(""))
            title = JOptionPane.showInputDialog("Title:");
        if (title == null) title = "";
        setTitle(title);

        // Set up the file chooser to show XML files, to select the preferences.xml file.
        final JFileChooser chooser = new JFileChooser();
        chooser.setCurrentDirectory(new File("."));
        chooser.setFileFilter(new FileNameExtensionFilter("XML files", "xml"));

        // Set up the menus.
        JMenuBar menuBar = new JMenuBar();
        setJMenuBar(menuBar);
        JMenu menu = new JMenu("File");
        menuBar.add(menu);

        JMenuItem exportItem = new JMenuItem("Export Preferences");
        menu.add(exportItem);
        exportItem.addActionListener(event -> {
            if (chooser.showSaveDialog(PreferencesFrame.this) == JFileChooser.APPROVE_OPTION) {
                try {
                    savePreferences();
                    OutputStream out = new FileOutputStream(chooser.getSelectedFile());
                    node.exportSubtree(out);
                    out.close();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });

        JMenuItem importItem = new JMenuItem("Import Preferences");
        menu.add(importItem);
        importItem.addActionListener(event -> {
            if (chooser.showSaveDialog(PreferencesFrame.this) == JFileChooser.APPROVE_OPTION) {
                try {
                    InputStream in = new FileInputStream(chooser.getSelectedFile());
                    Preferences.importPreferences(in);
                    in.close();
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });

        JMenuItem exitItem = new JMenuItem("Exit");
        menu.add(exitItem);
        exitItem.addActionListener(event -> {
            savePreferences();
            System.exit(0);
        });
    }

    public void savePreferences() {
        node.putInt("left", getX());
        node.putInt("top", getY());
        node.putInt("width", getWidth());
        node.putInt("height", getHeight());
        node.put("title", getTitle());
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE preferences SYSTEM "http://java.sun.com/dtd/preferences.dtd">
<preferences EXTERNAL_XML_VERSION="1.0">
  <root type="user">
  <map/>
  <node name="com">
    <map/>
    <node name="horstmann">
      <map/>
      <node name="corejava">
        <map>
          <entry key="left" value="11"/>
          <entry key="top" value="9"/>
          <entry key="width" value="453"/>
          <entry key="height" value="365"/>
          <entry key="title" value="Hello, World!"/>
        </map>
        </node>
      </node>
    </node>
  </root>
</preferences>

1. PreferencesTest.java.13: error: cannot find symbol       
   frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   symbol: method setDefaultCloseOperation(int)
   class PreferencesFrame

2. PreferencesTest.java:49: error: cannot find symbol setJMenuBar(menuBar);
   symbol: method setJMenuBar(JMenuBar)
   class PreferencesFrame