java记事本运用Java知识设计并实现记事本，实现新建文件、打开文件、保存、另存为、复制、粘贴、字体设置等功能。

好的，以下是一个简单的Java记事本的实现：

import java.awt.BorderLayout;
import java.awt.Font;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.KeyStroke;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.filechooser.FileNameExtensionFilter;

public class JavaNotepad implements ActionListener {
    private JFrame frame;
    private JTextArea textArea;
    private JScrollPane scrollPane;
    private JMenuBar menuBar;
    private JMenu fileMenu;
    private JMenu editMenu;
    private JMenu formatMenu;
    private JMenuItem newMenuItem;
    private JMenuItem openMenuItem;
    private JMenuItem saveMenuItem;
    private JMenuItem saveAsMenuItem;
    private JMenuItem exitMenuItem;
    private JMenuItem cutMenuItem;
    private JMenuItem copyMenuItem;
    private JMenuItem pasteMenuItem;
    private JMenuItem selectAllMenuItem;
    private JMenuItem fontMenuItem;
    private JFileChooser fileChooser;

    public JavaNotepad() {
        frame = new JFrame("Java Notepad");
        textArea = new JTextArea();
        scrollPane = new JScrollPane(textArea);
        menuBar = new JMenuBar();
        fileMenu = new JMenu("File");
        editMenu = new JMenu("Edit");
        formatMenu = new JMenu("Format");
        newMenuItem = new JMenuItem("New");
        openMenuItem = new JMenuItem("Open");
        saveMenuItem = new JMenuItem("Save");
        saveAsMenuItem = new JMenuItem("Save As");
        exitMenuItem = new JMenuItem("Exit");
        cutMenuItem = new JMenuItem("Cut");
        copyMenuItem = new JMenuItem("Copy");
        pasteMenuItem = new JMenuItem("Paste");
        selectAllMenuItem = new JMenuItem("Select All");
        fontMenuItem = new JMenuItem("Font");
        fileChooser = new JFileChooser();

        // 设置快捷键
        newMenuItem.setAccelerator(KeyStroke.getKeyStroke("control N"));
        openMenuItem.setAccelerator(KeyStroke.getKeyStroke("control O"));
        saveMenuItem.setAccelerator(KeyStroke.getKeyStroke("control S"));
        cutMenuItem.setAccelerator(KeyStroke.getKeyStroke("control X"));
        copyMenuItem.setAccelerator(KeyStroke.getKeyStroke("control C"));
        pasteMenuItem.setAccelerator(KeyStroke.getKeyStroke("control V"));
        selectAllMenuItem.setAccelerator(KeyStroke.getKeyStroke("control A"));
        fontMenuItem.setAccelerator(KeyStroke.getKeyStroke("control F"));

        // 添加菜单项
        fileMenu.add(newMenuItem);
        fileMenu.add(openMenuItem);
        fileMenu.addSeparator();
        fileMenu.add(saveMenuItem);
        fileMenu.add(saveAsMenuItem);
        fileMenu.addSeparator();
        fileMenu.add(exitMenuItem);
        editMenu.add(cutMenuItem);
        editMenu.add(copyMenuItem);
        editMenu.add(pasteMenuItem);
        editMenu.addSeparator();
        editMenu.add(selectAllMenuItem);
        formatMenu.add(fontMenuItem);
        menuBar.add(fileMenu);
        menuBar.add(editMenu);
        menuBar.add(formatMenu);
        frame.setJMenuBar(menuBar);

        // 添加事件监听器
        newMenuItem.addActionListener(this);
        openMenuItem.addActionListener(this);
        saveMenuItem.addActionListener(this);
        saveAsMenuItem.addActionListener(this);
        exitMenuItem.addActionListener(this);
        cutMenuItem.addActionListener(this);
        copyMenuItem.addActionListener(this);
        pasteMenuItem.addActionListener(this);
        selectAllMenuItem.addActionListener(this);
        fontMenuItem.addActionListener(this);

        // 设置文本区域字体
        textArea.setFont(new Font("宋体", Font.PLAIN, 16));

        frame.add(scrollPane, BorderLayout.CENTER);
        frame.setSize(600, 400);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        // 设置界面样式
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (ClassNotFoundException | InstantiationException | IllegalAccessException
                | UnsupportedLookAndFeelException e) {
            e.printStackTrace();
        }
        new JavaNotepad();
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == newMenuItem) {
            // 新建文件
            textArea.setText("");
            frame.setTitle("Java Notepad");
        } else if (e.getSource() == openMenuItem) {
            // 打开文件
            FileNameExtensionFilter filter = new FileNameExtensionFilter("文本文件(*.txt)", "txt");
            fileChooser.setFileFilter(filter);
            int result = fileChooser.showOpenDialog(frame);
            if (result == JFileChooser.APPROVE_OPTION) {
                File file = fileChooser.getSelectedFile();
                try {
                    BufferedReader reader = new BufferedReader(new FileReader(file));
                    String line;
                    StringBuilder sb = new StringBuilder();
                    while ((line = reader.readLine()) != null) {
                        sb.append(line).append("\n");
                    }
                    reader.close();
                    textArea.setText(sb.toString());
                    frame.setTitle(file.getName() + " - Java Notepad");
                } catch (Exception ex) {
                    JOptionPane.showMessageDialog(frame, "打开文件失败！");
                }
            }
        } else if (e.getSource() == saveMenuItem) {
            // 保存文件
            File file = fileChooser.getSelectedFile();
            if (file != null) {
                try {
                    BufferedWriter writer = new BufferedWriter(new FileWriter(file));
                    writer.write(textArea.getText());
                    writer.close();
                    frame.setTitle(file.getName() + " - Java Notepad");
                } catch (Exception ex) {
                    JOptionPane.showMessageDialog(frame, "保存文件失败！");
                }
            } else {
                saveAs();
            }
        } else if (e.getSource() == saveAsMenuItem) {
            // 另存为
            saveAs();
        } else if (e.getSource() == exitMenuItem) {
            // 退出程序
            System.exit(0);
        } else if (e.getSource() == cutMenuItem) {
            // 剪切
            textArea.cut();
        } else if (e.getSource() == copyMenuItem) {
            // 复制
            textArea.copy();
        } else if (e.getSource() == pasteMenuItem) {
            // 粘贴
            textArea.paste();
        } else if (e.getSource() == selectAllMenuItem) {
            // 全选
            textArea.selectAll();
        } else if (e.getSource() == fontMenuItem) {
            // 字体设置
            Font font = textArea.getFont();
            Font newFont = JFontChooser.showDialog(frame, "选择字体", font);
            if (newFont != null) {
                textArea.setFont(newFont);
            }
        }
    }

    private void saveAs() {
        FileNameExtensionFilter filter = new FileNameExtensionFilter("文本文件(*.txt)", "txt");
        fileChooser.setFileFilter(filter);
        int result = fileChooser.showSaveDialog(frame);
        if (result == JFileChooser.APPROVE_OPTION) {
            File file = fileChooser.getSelectedFile();
            if (!file.getName().endsWith(".txt")) {
                file = new File(file.getParentFile(), file.getName() + ".txt");
            }
            try {
                BufferedWriter writer = new BufferedWriter(new FileWriter(file));
                writer.write(textArea.getText());
                writer.close();
                frame.setTitle(file.getName() + " - Java Notepad");
            } catch (Exception ex) {
                JOptionPane.showMessageDialog(frame, "保存文件失败！");
            }
        }
    }
}

这个记事本程序实现了新建文件、打开文件、保存、另存为、复制、粘贴、字体设置等功能。其中，JFileChooser组件用于选择文件路径，File类用于读写文件，JTextArea组件用于显示文本内容，JFontChooser组件用于选择字体。同时，使用了Swing库中的JMenuBar、JMenu、JMenuItem等组件来实现菜单栏和菜单项的添加和事件处理。