1.選單的包含關係

下面是一個簡單的示例：

需求：實現一個簡單的記事本，功能包括：開啟，儲存，退出

import java.awt.*;
import java.awt.event.*;
import java.io.*;
class MenuDemo 
{
	public static void main(String[] args) 
	{
		new myMenu();
	}
}
class myMenu
{
	private Frame f;
	private MenuBar bar;
	private Menu fileMenu;
	private MenuItem openMenuItem;
	private MenuItem saveMenuItem;
	private MenuItem exitMenuItem;
	private TextArea ta;
	private File file;
	private FileDialog openDia;
	private FileDialog saveDia;
	myMenu()
	{
		init();
	}
	public void init()
	{
		f=new Frame("My Frame");
		f.setBounds(500,400,600,500);
		bar=new MenuBar();
		fileMenu=new Menu("選單");
		openMenuItem=new MenuItem("開啟");
		saveMenuItem=new MenuItem("儲存");
		exitMenuItem=new MenuItem("退出");
		fileMenu.add(openMenuItem);
		fileMenu.add(saveMenuItem);
		fileMenu.add(exitMenuItem);
		ta=new TextArea();
		bar.add(fileMenu);
		f.setMenuBar(bar);
		f.add(ta);
		myEvent();
		f.setVisible(true);
	}
	public void myEvent()
	{
		//窗體關閉事件
		f.addWindowListener(new WindowAdapter()
		{
			public void windowClosing(WindowEvent e)
			{
				System.exit(0);
			}
		});
		//退出子條目事件
		exitMenuItem.addActionListener(new ActionListener()
		{
			public void actionPerformed(ActionEvent e)
			{
				System.exit(0);
			}
		});
		//為openDia子條目新增開啟事件
		openMenuItem.addActionListener(new ActionListener()
		{
			public void actionPerformed(ActionEvent e)
			{
				openDia=new FileDialog(f,"開啟",FileDialog.LOAD);
				openDia.setVisible(true);
				String DirPath=openDia.getDirectory();
				String filename=openDia.getFile();				
				if(DirPath==null || filename==null)
					return;
				file=new File(DirPath,filename);
				ta.setText("");
				try
				{
					BufferedReader bufr=new BufferedReader(new FileReader(file));
					String line=null;
					while((line=bufr.readLine())!=null)
					{
						ta.append(line+"\r\n");
					}
				}
				catch (IOException ex)
				{
					throw new RuntimeException("關閉流失敗");
				}
			}
		});
		//為saveDia子條目新增事件
		saveMenuItem.addActionListener(new ActionListener()
		{
			public void actionPerformed(ActionEvent e)
			{
				if(file==null)
				{
					saveDia=new FileDialog(f,"儲存",FileDialog.SAVE);
					saveDia.setVisible(true);
					String DirPath=saveDia.getDirectory();
					String filename=saveDia.getFile();
					if(DirPath==null || filename==null)
						return;
					File file=new File(DirPath,filename);
				}
				try
				{
					BufferedWriter bufw=new BufferedWriter(new FileWriter(file));
					String text=ta.getText();
					bufw.write(text);
					bufw.close();
				}
				catch (IOException ex)
				{
					throw new RuntimeException("關閉流失敗");
				}
			}
		});
	}
}