填空题

本题的功能是获得系统剪贴板中的内容。窗口中有一个菜单“Edit”和一个文本域，“Edit”中有菜单项“Cut”、“Copy”和“Paste”，在文本域中输入内容，可以通过菜单进行剪切、复制和粘贴操作，如果系统剪贴板为空，又做粘贴操作的话，则设置文本域中背景颜色为红色，并显示错误信息。
import java. awt. * ;
import java. io. * ;
import java. awt. datatransfer. * ;
import java. awt. event. * ;
class java3 extends Frame implements ActionListener,
ClipboardOwner
TextArea textArea=new TextArea();
java3()
super("java3");
addWindowListener(new WindowAdapter()
public void windowClosing(WindowEvent e)
System. exit(0);
/);
MenuBar mb=new MenuBar();
Menu m=new Menu("Edit");
setLayout(new BorderLayout());
add("Center", textArea);
m. add("Cut");
m. add("Copy");
m. add("Paste");
mb. add(m);
setMenuBar(this);
for (int i=0; i＜m. getItemCount(); i++)
m. item(i). addActionListener(this);
setSize(300,300);
show();

public void actionPerformed(ActionEvent evt)
if ("Paste". equals(evt, getActionCommand()))
boolean error=true;
Transferable t=
getToolkit(). getSystemClipboard(). getContents(this);
try
if(t ! =null & &. t. isDataFlavorSupported(DataFlavor, stringFlavor))
textArea. setBackground(Color, white);
textArea. setForeground(Color, black);
textArea. replaceRange(
(String) t. getTransferData(DataFlavor. stringFlavor),
textArea. getSelectionStart(),
textArea. getSelectionEnd());
error=false;

catch(UnsupportedFlavorException e)
catch(IOException e)

if (error)
textArea. setBackground(Color, red);
textArea. setForeground(Color, white);
textArea. repaint();
textArea. setText("ERROR:\nEither the clipboard"+" is empty or the contents is not a string.");
else if ("Copy". equals(evt. getActionCommand
()))
setContents();
else if ("Cut". equals (evt. getActionCommand
()))
setContents ();
textArea. replaceRange("", textArea. getSelectionStart(), textArea. getSelectionEnd());


void setContents()
S=textArea. getSelectedText();
StringSelection contents=new StringSelection(s);
getToolkit(). getSystemClipboard(). setContents(contents, this);

public void lostOwnership (Clipboard clipboard, Transferable contents)
System. out. println("lost ownership");
public static void main(String args[])
new java3();