用java编写一个记事本程序能在eclipse且文件菜单上包含打开、保存和退出功能

编写一个简单的记事本程序，我们可以在Eclipse环境中创建一个新的Java SWT应用，因为SWT提供了一个简洁的界面控件库。这里是一个基本框架，包含了文件菜单上的打开、保存和退出操作：

import org.eclipse.swt.*;
import org.eclipse.swt.widgets.*;
import org.eclipse.jface.dialogs.MessageDialog;
import java.io.*;

public class NotepadApp extends Shell {
    
    private Text textArea;
    private Menu menuBar;
    private MenuItem openItem;
    private MenuItem saveItem;
    private MenuItem exitItem;

    public NotepadApp() {
        super("简易记事本");

        // 设置窗口样式
        Style style = new Style();
        style.configure(Shell.TITLE_BAR | Shell.CLOSE | Shell.MIN | Shell.MAX);

        // 创建文本区域
        textArea = new Text(this, SWT.MULTI | SWT.V_SCROLL);
        textArea.setBounds(0, 0, 400, 300);

        // 创建菜单栏
        menuBar = new Menu(this);
        setMenuBar(menuBar);

        // 创建菜单项
        createMenuItems();
    }

    private void createMenuItems() {
        openItem = new MenuItem(menuBar, SWT.PUSH);
        openItem.setText("&打开");
        openItem.addSelectionListener(e -> handleOpenFile());

        saveItem = new MenuItem(menuBar, SWT.PUSH);
        saveItem.setText("&保存");
        saveItem.addSelectionListener(e -> handleSaveFile());

        exitItem = new MenuItem(menuBar, SWT.PUSH);
        exitItem.setText("&退出");
        exitItem.addSelectionListener(e -> handleExit());
    }

    private void handleOpenFile() {
        FileDialog dialog = new FileDialog(this, SWT.OPEN);
        if (dialog.open() != null) {
            try (BufferedReader reader = new BufferedReader(new FileReader(dialog.getFile()))) {
                String line;
                while ((line = reader.readLine()) != null) {
                    textArea.append(line + "\n");
                }
            } catch (IOException e) {
                MessageDialog.openError(this, "错误", "无法打开文件: " + e.getMessage());
            }
        }
    }

    private void handleSaveFile() {
        FileDialog dialog = new FileDialog(this, SWT.SAVE);
        if (dialog.open() != null) {
            try (PrintWriter writer = new PrintWriter(new FileWriter(dialog.getFile()))) {
                writer.println(textArea.getText());
            } catch (IOException e) {
                MessageDialog.openError(this, "错误", "无法保存文件: " + e.getMessage());
            }
        }
    }

    private void handleExit() {
        if (!textArea.getText().isEmpty()) {
            int result = MessageDialog.openQuestion(this, "确认", "是否保存未更改的内容?");
            if (result == MessageBox.OK) {
                handleSaveFile();
            }
        }
        dispose();
    }

    // 主函数启动应用程序
    public static void main(String[] args) {
        Display display = new Display();
        final NotepadApp app = new NotepadApp();
        app.open();
        display.dispose();
    }
}