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我是一名新手 Java 程序员。我试图编辑一个 Java 应用程序，该应用程序基本上是一个下载管理器。它有一个文本字段，我们必须在其中粘贴 URL 以下载该特定文件。现在我的问题是我正在尝试添加一个鼠标事件，以便我可以右键单击并将 URL“粘贴”到文本字段中。我还想为右键单击添加“剪切”和“复制”选项。但是我尝试了很多东西，都没有达到我想要的。

如果有人可以通过给我一个代码示例来帮助我完成这项工作，那将有很大帮助。我想知道通过右键单击文本字段来获得“剪切”、“复制”和“粘贴”菜单的最简单方法。

谢谢你。

我正在修改的下载管理器应用程序的部分源代码。 

public class FTPDownloader extends JFrame implements Observer {

private JTextField addTextField = new JTextField(40);

private DownloadsTableModel tableModel = new DownloadsTableModel();

private JTable table;

private JButton pauseButton = new JButton("Pause");

private JButton resumeButton = new JButton("Resume");

private JButton cancelButton, clearButton;

private JLabel saveFileLabel = new JLabel();

private Download selectedDownload;

private boolean clearing;

public FTPDownloader() {
setTitle("FTP Download Manager");
setSize(740, 480);
setLocationRelativeTo(null); 
addWindowListener(new WindowAdapter() {
@Override
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
JMenuBar menuBar = new JMenuBar();
JMenu fileMenu = new JMenu("File");
fileMenu.setMnemonic(KeyEvent.VK_F);
JMenuItem fileExitMenuItem = new JMenuItem("Exit", KeyEvent.VK_X);
JMenuItem fileOpenMenuItem = new JMenuItem("Open", KeyEvent.VK_O);
fileExitMenuItem.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
System.exit(0);
}
});
fileOpenMenuItem.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
actionSaveTo();
}
});
fileMenu.add(fileOpenMenuItem);
fileMenu.add(fileExitMenuItem);
menuBar.add(fileMenu);
setJMenuBar(menuBar);

// Set up add panel.
JPanel addPanel = new JPanel(new BorderLayout());

JPanel targetPanel = new JPanel(new BorderLayout());
targetPanel.add(addTextField, BorderLayout.WEST);
JButton addButton = new JButton("Add Download");
addButton.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
actionAdd();
}
});

targetPanel.add(addButton, BorderLayout.EAST);

JPanel destinationPanel = new JPanel(new BorderLayout());
saveFileLabel.setText("File:");
destinationPanel.add(saveFileLabel, BorderLayout.WEST);

JButton saveFileButton = new JButton("Download To");
saveFileButton.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
actionSaveTo();
}
});
destinationPanel.add(saveFileButton, BorderLayout.EAST);
addPanel.add(destinationPanel, BorderLayout.NORTH);
addPanel.add(targetPanel, BorderLayout.SOUTH);

// Set up Downloads table.

table = new JTable(tableModel);
table.getSelectionModel().addListSelectionListener(new ListSelectionListener() {
@Override
public void valueChanged(ListSelectionEvent e) {
tableSelectionChanged();
}
});
table.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);

ProgressRenderer renderer = new ProgressRenderer(0, 100);
renderer.setStringPainted(true); // show progress text
table.setDefaultRenderer(JProgressBar.class, renderer);

table.setRowHeight((int) renderer.getPreferredSize().getHeight());

JPanel downloadsPanel = new JPanel();
downloadsPanel.setBorder(BorderFactory.createTitledBorder("Downloads"));
downloadsPanel.setLayout(new BorderLayout());
downloadsPanel.add(new JScrollPane(table), BorderLayout.CENTER);

JPanel buttonsPanel = new JPanel();

pauseButton.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
actionPause();
}
});
pauseButton.setEnabled(false);
buttonsPanel.add(pauseButton);

resumeButton.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
actionResume();
}
});
resumeButton.setEnabled(false);
buttonsPanel.add(resumeButton);
cancelButton = new JButton("Cancel");
cancelButton.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
actionCancel();
}
});
cancelButton.setEnabled(false);
buttonsPanel.add(cancelButton);
clearButton = new JButton("Clear");
clearButton.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
actionClear();
}
});
clearButton.setEnabled(false);
buttonsPanel.add(clearButton);

getContentPane().setLayout(new BorderLayout());
getContentPane().add(addPanel, BorderLayout.NORTH);
getContentPane().add(downloadsPanel, BorderLayout.CENTER);
getContentPane().add(buttonsPanel, BorderLayout.SOUTH);
}

private void actionSaveTo()
{

JFileChooser jfchooser = new JFileChooser();

jfchooser.setApproveButtonText("OK");
jfchooser.setDialogTitle("Save To");
jfchooser.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);

int result = jfchooser.showOpenDialog(this);
File newZipFile = jfchooser.getSelectedFile();
System.out.println("importProfile:" + newZipFile);
this.saveFileLabel.setText(newZipFile.getPath());

}

private void actionAdd() {
URL verifiedUrl = verifyUrl(addTextField.getText());
if (verifiedUrl != null) {
tableModel.addDownload(new Download(verifiedUrl, saveFileLabel.getText()));
addTextField.setText(""); // reset add text field
} else {
JOptionPane.showMessageDialog(this, "Invalid Download URL", "Error",
JOptionPane.ERROR_MESSAGE);
}
}

private URL verifyUrl(String url) {
if (!url.toLowerCase().startsWith("http://"))
return null;


URL verifiedUrl = null;
try {
verifiedUrl = new URL(url);
} catch (Exception e) {
return null;
}

if (verifiedUrl.getFile().length() < 2)
return null;

return verifiedUrl;
}

private void tableSelectionChanged() {
if (selectedDownload != null)
selectedDownload.deleteObserver(FTPDownloader.this);

if (!clearing && table.getSelectedRow() > -1) {
selectedDownload = tableModel.getDownload(table.getSelectedRow());
selectedDownload.addObserver(FTPDownloader.this);
updateButtons();
}
}

private void actionPause() {
selectedDownload.pause();
updateButtons();
}

private void actionResume() {
selectedDownload.resume();
updateButtons();
}

private void actionCancel() {
selectedDownload.cancel();
updateButtons();
}

private void actionClear() {
clearing = true;
tableModel.clearDownload(table.getSelectedRow());
clearing = false;
selectedDownload = null;
updateButtons();
}

private void updateButtons() {
if (selectedDownload != null) {
int status = selectedDownload.getStatus();
switch (status) {
case Download.DOWNLOADING:
pauseButton.setEnabled(true);
resumeButton.setEnabled(false);
cancelButton.setEnabled(true);
clearButton.setEnabled(false);
break;
case Download.PAUSED:
pauseButton.setEnabled(false);
resumeButton.setEnabled(true);
cancelButton.setEnabled(true);
clearButton.setEnabled(false);
break;
case Download.ERROR:
pauseButton.setEnabled(false);
resumeButton.setEnabled(true);
cancelButton.setEnabled(false);
clearButton.setEnabled(true);
break;
default: // COMPLETE or CANCELLED
pauseButton.setEnabled(false);
resumeButton.setEnabled(false);
cancelButton.setEnabled(false);
clearButton.setEnabled(true);
}
} else {
pauseButton.setEnabled(false);
resumeButton.setEnabled(false);
cancelButton.setEnabled(false);
clearButton.setEnabled(false);
}
}

public void update(Observable o, Object arg) {
// Update buttons if the selected download has changed.
if (selectedDownload != null && selectedDownload.equals(o))
updateButtons();
}
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