java怎么编写记事本程序

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要编写一个简单的记事本程序，你可以使用 Java GUI 库（如 Swing 或 JavaFX）来创建用户界面，并使用 Java 文件 IO 操作来读取和写入文本文件。

下面是一个使用 Swing 库来创建一个简单记事本程序的例子：

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

public class Notepad extends JFrame {private JTextArea textArea;
    private JFileChooser fileChooser;

    public Notepad() {super(" 记事本 ");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(800, 600);

        textArea = new JTextArea();
        JScrollPane scrollPane = new JScrollPane(textArea);
        add(scrollPane, BorderLayout.CENTER);

        fileChooser = new JFileChooser();

        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 exitMenuItem = new JMenuItem(" 退出 ");

        newMenuItem.addActionListener(new NewActionListener());
        openMenuItem.addActionListener(new OpenActionListener());
        saveMenuItem.addActionListener(new SaveActionListener());
        exitMenuItem.addActionListener(new ExitActionListener());

        fileMenu.add(newMenuItem);
        fileMenu.add(openMenuItem);
        fileMenu.add(saveMenuItem);
        fileMenu.add(exitMenuItem);

        menuBar.add(fileMenu);
        setJMenuBar(menuBar);
    }

    private class NewActionListener implements ActionListener {@Override
        public void actionPerformed(ActionEvent e) {textArea.setText("");
        }
    }

    private class OpenActionListener implements ActionListener {@Override
        public void actionPerformed(ActionEvent e) {int returnVal = fileChooser.showOpenDialog(Notepad.this);
            if (returnVal == JFileChooser.APPROVE_OPTION) {File file = fileChooser.getSelectedFile();
                try {BufferedReader reader = new BufferedReader(new FileReader(file));
                    StringBuilder sb = new StringBuilder();
                    String line;
                    while ((line = reader.readLine()) != null) {sb.append(line).append("\n");
                    }
                    reader.close();
                    textArea.setText(sb.toString());
                } catch (IOException ex) {ex.printStackTrace();
                }
            }
        }
    }

    private class SaveActionListener implements ActionListener {@Override
        public void actionPerformed(ActionEvent e) {int returnVal = fileChooser.showSaveDialog(Notepad.this);
            if (returnVal == JFileChooser.APPROVE_OPTION) {File file = fileChooser.getSelectedFile();
                try {BufferedWriter writer = new BufferedWriter(new FileWriter(file));
                    writer.write(textArea.getText());
                    writer.close();} catch (IOException ex) {ex.printStackTrace();
                }
            }
        }
    }

    private class ExitActionListener implements ActionListener {@Override
        public void actionPerformed(ActionEvent e) {System.exit(0);
        }
    }

    public static void main(String[] args) {SwingUtilities.invokeLater(() -> {Notepad notepad = new Notepad();
            notepad.setVisible(true);
        });
    }
}