Java简单记事本开发教程

• JFrame承载整个程序界面
• JTextArea用于输入和显示文本内容
• 用JScrollPane包裹文本区域，实现滚动功能

• “新建”清空文本区域
• “打开”使用JFileChooser选择.txt文件并读取内容
• “保存”将当前文本写入指定文件
• “退出”关闭程序

• 打开文件前检查是否已选择有效文件
• 保存时可判断是否已有文件路径，否则弹出另存为对话框
• 异常处理避免程序因IO错误崩溃

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.nio.charset.StandardCharsets;
public class SimpleNotepad extends JFrame {
private JTextArea textArea;
private JFileChooser fileChooser;
private String currentFile = null;
public SimpleNotepad() {
    setTitle("简易记事本");
    setSize(600, 400);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

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

    // 菜单栏
    JMenuBar menuBar = new JMenuBar();
    JMenu fileMenu = new JMenu("文件");
    JMenuItem newItem = new JMenuItem("新建");
    JMenuItem openItem = new JMenuItem("打开");
    JMenuItem saveItem = new JMenuItem("保存");
    JMenuItem exitItem = new JMenuItem("退出");

    fileMenu.add(newItem);
    fileMenu.add(openItem);
    fileMenu.add(saveItem);
    fileMenu.addSeparator();
    fileMenu.add(exitItem);
    menuBar.add(fileMenu);
    setJMenuBar(menuBar);

    // 文件选择器
    fileChooser = new JFileChooser();
    fileChooser.setFileFilter(new javax.swing.filechooser.FileNameExtensionFilter("文本文件", "txt"));

    // 事件监听
    newItem.addActionListener(e -> newFile());
    openItem.addActionListener(e -> openFile());
    saveItem.addActionListener(e -> saveFile());
    exitItem.addActionListener(e -> System.exit(0));

    setLocationRelativeTo(null);
}

private void newFile() {
    if (textArea.getText().length() > 0) {
        int result = JOptionPane.showConfirmDialog(this, "是否保存当前内容？", "提示", JOptionPane.YES_NO_CANCEL_OPTION);
        if (result == JOptionPane.YES_OPTION) saveFile();
        else if (result == JOptionPane.CANCEL_OPTION) return;
    }
    textArea.setText("");
    currentFile = null;
}

private void openFile() {
    int result = fileChooser.showOpenDialog(this);
    if (result == JFileChooser.APPROVE_OPTION) {
        File file = fileChooser.getSelectedFile();
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(file), StandardCharsets.UTF_8))) {
            StringBuilder content = new StringBuilder();
            String line;
            while ((line = reader.readLine()) != null) {
                content.append(line).append("\n");
            }
            textArea.setText(content.toString());
            currentFile = file.getAbsolutePath();
            setTitle("简易记事本 - " + file.getName());
        } catch (IOException ex) {
            JOptionPane.showMessageDialog(this, "无法打开文件：" + ex.getMessage(), "错误", JOptionPane.ERROR_MESSAGE);
        }
    }
}

private void saveFile() {
    if (currentFile == null) {
        saveAs();
    } else {
        saveToFile(currentFile);
    }
}

private void saveAs() {
    int result = fileChooser.showSaveDialog(this);
    if (result == JFileChooser.APPROVE_OPTION) {
        File file = fileChooser.getSelectedFile();
        if (!file.getName().endsWith(".txt")) {
            file = new File(file.getParent(), file.getName() + ".txt");
        }
        saveToFile(file.getAbsolutePath());
        currentFile = file.getAbsolutePath();
        setTitle("简易记事本 - " + file.getName());
    }
}

private void saveToFile(String path) {
    try (BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(path), StandardCharsets.UTF_8))) {
        writer.write(textArea.getText());
    } catch (IOException ex) {
        JOptionPane.showMessageDialog(this, "保存失败：" + ex.getMessage(), "错误", JOptionPane.ERROR_MESSAGE);
    }
}

public static void main(String[] args) {
    SwingUtilities.invokeLater(() -> {
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeel());
        } catch (Exception e) {
            e.printStackTrace();
        }
        new SimpleNotepad().setVisible(true);
    });
}
}