showdocument.java

java的书上例子

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.net.URL;
import java.net.MalformedURLException;

/** 该小应用程序通过GetAppletContext()方法得到AppletContext类型的对象。
  * 在接口AppletContext中提供了方法showDocument()，用来请求浏览器显示一个
  * URL地址所对应的HTML文件 */
 
/** Applet类 */
public class ShowDocument extends Applet implements ActionListener
{
	URLWindow urlWindow;
	
	/** init()方法 */
	public void init()
	{
		Button button=new Button("Bring up URL window:");
		button.addActionListener(this);
		add(button);
		urlWindow=new URLWindow(getAppletContext());
		urlWindow.pack();
	}
	
	/** destroy()方法 */ 
	public void destroy()
	{
		urlWindow.setVisible(false);
		urlWindow=null;
	}
	
	/** actionPerformed()方法 */
	public void actionPerformed(ActionEvent e)
	{//选择按钮后弹出一个窗口与用户交互
		urlWindow.setVisible(true);
	}
}//ShowDocument类结束

/** 需弹出的窗口类定义 */
class URLWindow extends Frame implements ActionListener
{
	TextField urlField;
	Choice choice;
	AppletContext appletContext;
	
	/** 弹出的窗口类构造方法 */
	public URLWindow(AppletContext appletContext)
	{
		super("show a Document!");
		this.appletContext=appletContext;
		
		GridBagLayout gridBag=new GridBagLayout();
		GridBagConstraints c=new GridBagConstraints();
		setLayout(gridBag);
		
		Label label1=new Label("URL of document to show:",Label.RIGHT);
		gridBag.setConstraints(label1,c);
		add(label1);
		
		urlField=new TextField("http://www.tsinghua.edu.cn/",40);
		urlField.addActionListener(this);
		c.gridwidth=GridBagConstraints.REMAINDER;
		c.fill=GridBagConstraints.HORIZONTAL;
		c.weightx=1.0;
		gridBag.setConstraints(urlField,c);
		add(urlField);
		
		Label label2=new Label("Window/frame to show it in:",Label.RIGHT);
		c.gridwidth=1;
		c.weightx=0.0;
		gridBag.setConstraints(label2,c);
		add(label2);
		
		choice=new Choice();
		choice.addItem("(browser's choice)");
		choice.addItem("My Personal Window");
		choice.addItem("_blank");
		choice.addItem("_self");
		choice.addItem("_parent");
		choice.addItem("_top");
		c.fill=GridBagConstraints.NONE;
		c.gridwidth=GridBagConstraints.REMAINDER;
		c.anchor=GridBagConstraints.WEST;
		gridBag.setConstraints(choice,c);
		add(choice);
		
		Button button=new Button("Show document");
		button.addActionListener(this);
		c.weighty=1.0;
		c.ipadx=10;
		c.ipady=10;
		c.insets=new Insets(5,0,0,0);
		c.anchor=GridBagConstraints.SOUTH;
		gridBag.setConstraints(button,c);
		add(button);
		
		addWindowListener(new WindowAdapter()
		{//关闭弹出窗口的匿名类
			public void windowClosing(WindowEvent e)
			{
				setVisible(false);
			}
		});
	}//构造方法结束
	
	/** 动作事件处理方法，选择”Show document”按钮后在指定的窗口中显示给定的URL地址主页 */
	public void actionPerformed(ActionEvent e)
	{
		String urlString=urlField.getText();
		URL url=null;
		try
		{
			url=new URL(urlString);
		}catch(MalformedURLException e1)
		{
			System.out.println("Malformed URL:"+urlString);
		}
		
		if (url!=null)
		{
			if (choice.getSelectedIndex()==0)
			{
				appletContext.showDocument(url);
			}else
			{
				appletContext.showDocument(url,choice.getSelectedItem());
			}
		}
	}//actionPerformed()方法结束
}//URLWindow类结束