记事本java代码实现新建打开保存另存为退出

好的，以下是一个简单的记事本 Java 代码，实现了新建、打开、保存、另存为和退出功能：

import java.awt.BorderLayout;
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.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.UIManager;
import javax.swing.filechooser.FileNameExtensionFilter;

public class Notepad extends JFrame implements ActionListener {

    private static final long serialVersionUID = 1L;
    private JTextArea textArea;
    private JFileChooser fileChooser;
    private String fileName;

    public Notepad() {
        super("记事本");

        // 设置菜单栏
        JMenuBar menuBar = new JMenuBar();
        JMenu fileMenu = new JMenu("文件");
        JMenuItem newMenuItem = new JMenuItem("新建");
        JMenuItem openMenuItem = new JMenuItem("打开");
        JMenuItem saveMenuItem = new JMenuItem("保存");
        JMenuItem saveAsMenuItem = new JMenuItem("另存为");
        JMenuItem exitMenuItem = new JMenuItem("退出");

        newMenuItem.addActionListener(this);
        openMenuItem.addActionListener(this);
        saveMenuItem.addActionListener(this);
        saveAsMenuItem.addActionListener(this);
        exitMenuItem.addActionListener(this);

        fileMenu.add(newMenuItem);
        fileMenu.add(openMenuItem);
        fileMenu.add(saveMenuItem);
        fileMenu.add(saveAsMenuItem);
        fileMenu.addSeparator();
        fileMenu.add(exitMenuItem);
        menuBar.add(fileMenu);

        setJMenuBar(menuBar);

        // 设置文本区域
        textArea = new JTextArea();
        JScrollPane scrollPane = new JScrollPane(textArea);
        getContentPane().add(scrollPane, BorderLayout.CENTER);

        // 设置文件选择器
        fileChooser = new JFileChooser();
        fileChooser.setFileFilter(new FileNameExtensionFilter("文本文件(*.txt)", "txt"));

        // 设置窗口
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(800, 600);
        setLocationRelativeTo(null);
        setVisible(true);
    }

    public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (Exception e) {
            e.printStackTrace();
        }
        new Notepad();
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        String command = e.getActionCommand();
        switch (command) {
        case "新建":
            newFile();
            break;
        case "打开":
            openFile();
            break;
        case "保存":
            saveFile();
            break;
        case "另存为":
            saveAsFile();
            break;
        case "退出":
            exit();
            break;
        }
    }

    // 新建文件
    private void newFile() {
        if (textArea.getText().length() > 0) {
            int option = JOptionPane.showConfirmDialog(this, "是否保存更改？", "记事本", JOptionPane.YES_NO_CANCEL_OPTION);
            if (option == JOptionPane.YES_OPTION) {
                saveFile();
            } else if (option == JOptionPane.CANCEL_OPTION) {
                return;
            }
        }
        textArea.setText("");
        fileName = null;
    }

    // 打开文件
    private void openFile() {
        if (textArea.getText().length() > 0) {
            int option = JOptionPane.showConfirmDialog(this, "是否保存更改？", "记事本", JOptionPane.YES_NO_CANCEL_OPTION);
            if (option == JOptionPane.YES_OPTION) {
                saveFile();
            } else if (option == JOptionPane.CANCEL_OPTION) {
                return;
            }
        }
        int result = fileChooser.showOpenDialog(this);
        if (result == JFileChooser.APPROVE_OPTION) {
            try {
                File file = fileChooser.getSelectedFile();
                fileName = file.getAbsolutePath();
                BufferedReader reader = new BufferedReader(new FileReader(file));
                String line = null;
                StringBuilder sb = new StringBuilder();
                while ((line = reader.readLine()) != null) {
                    sb.append(line);
                    sb.append(System.lineSeparator());
                }
                reader.close();
                textArea.setText(sb.toString());
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    // 保存文件
    private void saveFile() {
        if (fileName == null) {
            saveAsFile();
        } else {
            try {
                BufferedWriter writer = new BufferedWriter(new FileWriter(fileName));
                writer.write(textArea.getText());
                writer.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    // 另存为文件
    private void saveAsFile() {
        int result = fileChooser.showSaveDialog(this);
        if (result == JFileChooser.APPROVE_OPTION) {
            try {
                File file = fileChooser.getSelectedFile();
                if (!file.getName().endsWith(".txt")) {
                    file = new File(file.getAbsolutePath() + ".txt");
                }
                fileName = file.getAbsolutePath();
                BufferedWriter writer = new BufferedWriter(new FileWriter(file));
                writer.write(textArea.getText());
                writer.close();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    // 退出程序
    private void exit() {
        if (textArea.getText().length() > 0) {
            int option = JOptionPane.showConfirmDialog(this, "是否保存更改？", "记事本", JOptionPane.YES_NO_CANCEL_OPTION);
            if (option == JOptionPane.YES_OPTION) {
                saveFile();
            } else if (option == JOptionPane.CANCEL_OPTION) {
                return;
            }
        }
        System.exit(0);
    }
}

该记事本实现了新建、打开、保存、另存为和退出功能，可以选择文本文件进行编辑。