请用Java 写一个记事本，要求“文件”“编辑”“格式”“查看”“帮助”

以下是一个简单的Java记事本程序，实现了菜单栏的“文件”“编辑”“格式”“查看”“帮助”：

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class JavaNotepad extends JFrame implements ActionListener {
    JTextArea textArea;
    JScrollPane scrollPane;

    public JavaNotepad() {
        setTitle("Java Notepad");
        setSize(800, 600);
        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        JMenuBar menuBar = new JMenuBar();

        JMenu fileMenu = new JMenu("文件");
        JMenuItem newMenuItem = new JMenuItem("新建");
        newMenuItem.addActionListener(this);
        fileMenu.add(newMenuItem);
        JMenuItem openMenuItem = new JMenuItem("打开");
        openMenuItem.addActionListener(this);
        fileMenu.add(openMenuItem);
        JMenuItem saveMenuItem = new JMenuItem("保存");
        saveMenuItem.addActionListener(this);
        fileMenu.add(saveMenuItem);
        JMenuItem exitMenuItem = new JMenuItem("退出");
        exitMenuItem.addActionListener(this);
        fileMenu.add(exitMenuItem);
        menuBar.add(fileMenu);

        JMenu editMenu = new JMenu("编辑");
        JMenuItem cutMenuItem = new JMenuItem("剪切");
        cutMenuItem.addActionListener(this);
        editMenu.add(cutMenuItem);
        JMenuItem copyMenuItem = new JMenuItem("复制");
        copyMenuItem.addActionListener(this);
        editMenu.add(copyMenuItem);
        JMenuItem pasteMenuItem = new JMenuItem("粘贴");
        pasteMenuItem.addActionListener(this);
        editMenu.add(pasteMenuItem);
        menuBar.add(editMenu);

        JMenu formatMenu = new JMenu("格式");
        JMenuItem fontMenuItem = new JMenuItem("字体");
        fontMenuItem.addActionListener(this);
        formatMenu.add(fontMenuItem);
        menuBar.add(formatMenu);

        JMenu viewMenu = new JMenu("查看");
        JMenuItem zoomInMenuItem = new JMenuItem("放大");
        zoomInMenuItem.addActionListener(this);
        viewMenu.add(zoomInMenuItem);
        JMenuItem zoomOutMenuItem = new JMenuItem("缩小");
        zoomOutMenuItem.addActionListener(this);
        viewMenu.add(zoomOutMenuItem);
        menuBar.add(viewMenu);

        JMenu helpMenu = new JMenu("帮助");
        JMenuItem aboutMenuItem = new JMenuItem("关于");
        aboutMenuItem.addActionListener(this);
        helpMenu.add(aboutMenuItem);
        menuBar.add(helpMenu);

        setJMenuBar(menuBar);

        textArea = new JTextArea();
        scrollPane = new JScrollPane(textArea);
        add(scrollPane);

        setVisible(true);
    }

    public void actionPerformed(ActionEvent e) {
        String command = e.getActionCommand();
        switch (command) {
            case "新建":
                textArea.setText("");
                break;
            case "打开":
                JFileChooser openFileChooser = new JFileChooser();
                if (openFileChooser.showOpenDialog(this) == JFileChooser.APPROVE_OPTION) {
                    // 读取文件内容
                }
                break;
            case "保存":
                JFileChooser saveFileChooser = new JFileChooser();
                if (saveFileChooser.showSaveDialog(this) == JFileChooser.APPROVE_OPTION) {
                    // 写入文件内容
                }
                break;
            case "退出":
                System.exit(0);
                break;
            case "剪切":
                textArea.cut();
                break;
            case "复制":
                textArea.copy();
                break;
            case "粘贴":
                textArea.paste();
                break;
            case "字体":
                FontChooser fontChooser = new FontChooser(this);
                fontChooser.setVisible(true);
                break;
            case "放大":
                Font currentFont = textArea.getFont();
                float currentSize = currentFont.getSize2D();
                textArea.setFont(currentFont.deriveFont(currentSize + 2));
                break;
            case "缩小":
                Font currentFont2 = textArea.getFont();
                float currentSize2 = currentFont2.getSize2D();
                textArea.setFont(currentFont2.deriveFont(currentSize2 - 2));
                break;
            case "关于":
                JOptionPane.showMessageDialog(this, "Java Notepad v1.0");
                break;
        }
    }

    public static void main(String[] args) {
        new JavaNotepad();
    }

    class FontChooser extends JDialog implements ActionListener {
        JComboBox<String> fontComboBox;
        JComboBox<Integer> sizeComboBox;
        JCheckBox boldCheckBox;
        JCheckBox italicCheckBox;
        JButton okButton;
        JButton cancelButton;

        public FontChooser(Frame owner) {
            super(owner, "字体选择", true);
            setSize(400, 200);
            setLocationRelativeTo(null);

            JPanel panel = new JPanel();
            panel.setLayout(new GridLayout(4, 2));
            add(panel);

            fontComboBox = new JComboBox<>(GraphicsEnvironment.getLocalGraphicsEnvironment().getAvailableFontFamilyNames());
            panel.add(new JLabel("字体："));
            panel.add(fontComboBox);

            sizeComboBox = new JComboBox<>(new Integer[]{8, 9, 10, 11, 12, 14, 16, 18, 20, 22, 24, 26, 28, 36, 48, 72});
            panel.add(new JLabel("大小："));
            panel.add(sizeComboBox);

            boldCheckBox = new JCheckBox("粗体");
            panel.add(boldCheckBox);

            italicCheckBox = new JCheckBox("斜体");
            panel.add(italicCheckBox);

            okButton = new JButton("确定");
            okButton.addActionListener(this);
            panel.add(okButton);

            cancelButton = new JButton("取消");
            cancelButton.addActionListener(this);
            panel.add(cancelButton);

            Font currentFont = textArea.getFont();
            fontComboBox.setSelectedItem(currentFont.getFamily());
            sizeComboBox.setSelectedItem((int) currentFont.getSize2D());
            boldCheckBox.setSelected(currentFont.isBold());
            italicCheckBox.setSelected(currentFont.isItalic());
        }

        public void actionPerformed(ActionEvent e) {
            if (e.getSource() == okButton) {
                String fontName = (String) fontComboBox.getSelectedItem();
                int fontSize = (int) sizeComboBox.getSelectedItem();
                int fontStyle = 0;
                if (boldCheckBox.isSelected()) {
                    fontStyle += Font.BOLD;
                }
                if (italicCheckBox.isSelected()) {
                    fontStyle += Font.ITALIC;
                }
                textArea.setFont(new Font(fontName, fontStyle, fontSize));
            }
            setVisible(false);
        }
    }
}

注意：这只是一个简单的示例程序，对于实际的记事本程序，还有很多功能需要进一步完善和实现。