Java - 通过 NetBeans 为另一个类中的按钮添加监听器-6ren

Java - 通过 NetBeans 为另一个类中的按钮添加监听器

转载作者：行者123 更新时间：2023-12-01 09:16:45

*许多有关 GUI 的代码都是由 NetBeans 生成的。

我遇到的问题是在客户端，告诉我 uploadBtn 为 null，nullPointException。我很确定这是因为它没有实例化，并且我在构造函数中添加了一个 actionListener 。我通过 NetBeans 构建了 GUI，但不太确定如何去做。

我想要的是当单击uploadBtn时，客户端和服务器端都会发生一些事情。单击按钮后，它会调用在客户端为我创建的 NetBeans actionPerformed() NetBeans，但不确定如何检查服务器端是否按下了按钮，如果是的话，它会调用服务器中的方法。任何帮助表示赞赏。我正在使用套接字/数据报。大学项目。

ClientGUI.java

public class ClientGUI extends javax.swing.JFrame {

String username;

/**
 * Creates new form NewJFrame
 */
public ClientGUI() {
    initComponents();     
}

public ClientGUI(ActionListener listen)
{
    uploadBtn.addActionListener(listen);
}

/**
 * This method is called from within the constructor to initialize the form.
 * WARNING: Do NOT modify this code. The content of this method is always
 * regenerated by the Form Editor.
 */
@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">                          
private void initComponents() {

    jPanel1 = new javax.swing.JPanel();
    jLabel1 = new javax.swing.JLabel();
    usernameTxt = new javax.swing.JTextField();
    passwordTxt = new javax.swing.JTextField();
    loginBtn = new javax.swing.JButton();
    jLabel2 = new javax.swing.JLabel();
    jLabel3 = new javax.swing.JLabel();
    uploadBtn = new javax.swing.JButton();
    jLabel4 = new javax.swing.JLabel();
    downloadBtn = new javax.swing.JButton();
    logOffBtn = new javax.swing.JButton();
    portTxt = new javax.swing.JTextField();
    hostTxt = new javax.swing.JTextField();
    createFile = new javax.swing.JButton();
    fileNameTxt = new javax.swing.JTextField();
    connectionLbl = new javax.swing.JLabel();
    notifyLbl = new javax.swing.JLabel();
    downloadFileNameTxt = new javax.swing.JTextField();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

    jPanel1.setBackground(new java.awt.Color(0, 0, 51));

    jLabel1.setFont(new java.awt.Font("Tahoma", 0, 18)); // NOI18N
    jLabel1.setForeground(new java.awt.Color(255, 255, 255));
    jLabel1.setText("File Transfer System");

    usernameTxt.setText("Username");

    passwordTxt.setText("Password");

    loginBtn.setText("Login");
    loginBtn.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            loginBtnActionPerformed(evt);
        }
    });

    jLabel2.setFont(new java.awt.Font("Tahoma", 0, 14)); // NOI18N
    jLabel2.setForeground(new java.awt.Color(255, 255, 255));
    jLabel2.setText("Login");

    jLabel3.setFont(new java.awt.Font("Tahoma", 0, 14)); // NOI18N
    jLabel3.setForeground(new java.awt.Color(255, 255, 255));
    jLabel3.setText("Upload");

    uploadBtn.setText("Upload");
    uploadBtn.setName("Upload"); // NOI18N
    uploadBtn.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            uploadBtnActionPerformed(evt);
        }
    });

    jLabel4.setFont(new java.awt.Font("Tahoma", 0, 14)); // NOI18N
    jLabel4.setForeground(new java.awt.Color(255, 255, 255));
    jLabel4.setText("Download");

    downloadBtn.setText("Download");
    downloadBtn.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            downloadBtnActionPerformed(evt);
        }
    });

    logOffBtn.setBackground(new java.awt.Color(153, 0, 0));
    logOffBtn.setForeground(new java.awt.Color(255, 255, 255));
    logOffBtn.setText("Log Off");
    logOffBtn.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            logOffBtnActionPerformed(evt);
        }
    });

    portTxt.setText("7");
    portTxt.setToolTipText("Port");

    hostTxt.setText("localhost");

    createFile.setText("Create File");
    createFile.addActionListener(new java.awt.event.ActionListener() {
        public void actionPerformed(java.awt.event.ActionEvent evt) {
            createFileActionPerformed(evt);
        }
    });

    fileNameTxt.setText("File Name");

    connectionLbl.setFont(new java.awt.Font("Tahoma", 0, 14)); // NOI18N
    connectionLbl.setForeground(new java.awt.Color(255, 0, 0));
    connectionLbl.setText("Not Connected");

    notifyLbl.setFont(new java.awt.Font("Tahoma", 0, 12)); // NOI18N
    notifyLbl.setForeground(java.awt.Color.green);

    downloadFileNameTxt.setText("File Name");

    javax.swing.GroupLayout jPanel1Layout = new javax.swing.GroupLayout(jPanel1);
    jPanel1.setLayout(jPanel1Layout);
    jPanel1Layout.setHorizontalGroup(
        jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(jPanel1Layout.createSequentialGroup()
            .addGap(21, 21, 21)
            .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addGroup(jPanel1Layout.createSequentialGroup()
                    .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
                        .addComponent(portTxt, javax.swing.GroupLayout.Alignment.LEADING)
                        .addComponent(jLabel2, javax.swing.GroupLayout.Alignment.LEADING)
                        .addComponent(usernameTxt, javax.swing.GroupLayout.Alignment.LEADING)
                        .addComponent(passwordTxt, javax.swing.GroupLayout.Alignment.LEADING)
                        .addComponent(loginBtn, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, 82, Short.MAX_VALUE))
                    .addGap(101, 101, 101)
                    .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                        .addComponent(notifyLbl)
                        .addGroup(jPanel1Layout.createSequentialGroup()
                            .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.TRAILING, false)
                                .addComponent(fileNameTxt, javax.swing.GroupLayout.Alignment.LEADING)
                                .addComponent(jLabel3, javax.swing.GroupLayout.Alignment.LEADING)
                                .addComponent(createFile, javax.swing.GroupLayout.Alignment.LEADING, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                                .addComponent(uploadBtn, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE))
                            .addGap(115, 115, 115)
                            .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                                .addComponent(downloadFileNameTxt, javax.swing.GroupLayout.PREFERRED_SIZE, 85, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addComponent(jLabel4)
                                .addComponent(downloadBtn, javax.swing.GroupLayout.PREFERRED_SIZE, 85, javax.swing.GroupLayout.PREFERRED_SIZE)
                                .addComponent(logOffBtn)))))
                .addComponent(connectionLbl)
                .addComponent(hostTxt, javax.swing.GroupLayout.PREFERRED_SIZE, 82, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addGroup(jPanel1Layout.createSequentialGroup()
                    .addGap(152, 152, 152)
                    .addComponent(jLabel1)))
            .addContainerGap(49, Short.MAX_VALUE))
    );
    jPanel1Layout.setVerticalGroup(
        jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGroup(jPanel1Layout.createSequentialGroup()
            .addContainerGap()
            .addComponent(jLabel1)
            .addGap(26, 26, 26)
            .addComponent(connectionLbl)
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 53, Short.MAX_VALUE)
            .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(jLabel2)
                .addComponent(jLabel3)
                .addComponent(jLabel4))
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(usernameTxt, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addComponent(createFile)
                .addComponent(downloadFileNameTxt, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED)
            .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(passwordTxt, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addComponent(downloadBtn))
            .addGap(30, 30, 30)
            .addComponent(hostTxt, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
            .addGap(10, 10, 10)
            .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(portTxt, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addComponent(fileNameTxt, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE))
            .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
            .addGroup(jPanel1Layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                .addComponent(loginBtn)
                .addComponent(uploadBtn)
                .addComponent(logOffBtn))
            .addGap(42, 42, 42)
            .addComponent(notifyLbl)
            .addGap(36, 36, 36))
    );

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addComponent(jPanel1, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
    );

    pack();
}// </editor-fold>                        

private void loginBtnActionPerformed(java.awt.event.ActionEvent evt) {                                         
    try {

        String hostname = hostTxt.getText();
        String port = portTxt.getText();
        username = usernameTxt.getText();
        String password = passwordTxt.getText();
        ClientGUI client = new ClientGUI();

        Users usersClass = new Users();

        if (hostname.length() == 0) // if user did not enter a name
        {
            hostname = "localhost";  //   use the default host name
        }

        if (port.length() == 0) // if user did not enter a name
        {
            port = "7";  //   use the default host name
        }

        Map<String, String> users;
        users = usersClass.getSet();

        if (users.containsKey(username) && users.containsValue(password)) {
            JOptionPane.showMessageDialog(null, "Logged in Successfully. Welcome " + username);
            connectionLbl.setText("Connected");
            connectionLbl.setForeground(Color.green);
            hostTxt.setEditable(false);
            portTxt.setEditable(false);
            usernameTxt.setEditable(false);
            passwordTxt.setEditable(false);
            loginBtn.setEnabled(false);

            createUserFolder(username);
            new File("C:\\ServerFolder\\" + username).mkdirs();
        } else if (!users.containsKey(username) && !users.containsValue(password)) {
            JOptionPane.showMessageDialog(null, "User does not exist.  Try again.");
        }

        ClientHelper helper
                = new ClientHelper(hostname, port, username, password);

        boolean check = client.validateUsername(username);
        while (check) {
            String serverResponse = helper.sendMessageUsername(username);
            System.out.println(serverResponse);
            check = false;
        }

    } catch (SocketException ex) {
        Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
    } catch (UnknownHostException ex) {
        Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
    } catch (IOException ex) {
        Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
    }


}                                        

public File createUserFolder(String folderName) {
    File directory = new File("C:\\" + folderName);
// if the directory does not exist, create it
    if (!directory.exists()) {
        System.out.println("Creating Directory... ");
        boolean result = false;

        try {
            directory.mkdir();
            result = true;
        } catch (SecurityException se) {
            //handle it
        }
        if (result) {
            System.out.println("Directory Created");
        }
    }

    return directory;
}


public JButton getButton()
{
    return uploadBtn;
}

private void logOffBtnActionPerformed(java.awt.event.ActionEvent evt) {                                          

    //   try {
    String hostname = hostTxt.getText();
    String port = portTxt.getText();
    username = usernameTxt.getText();
    String password = passwordTxt.getText();
    hostTxt.setEditable(true);
    portTxt.setEditable(true);
    usernameTxt.setEditable(true);
    passwordTxt.setEditable(true);
    loginBtn.setEnabled(true);

    connectionLbl.setText("Not Connected");
    connectionLbl.setForeground(Color.red);

   //            ClientHelper helper
   //                    = new ClientHelper(hostname, port, username, password);
   //                   
    //                String serverResponse =helper.sendMessageLogOff(username);
   //                System.out.println(serverResponse);
   //                
   //            
   //        } catch (SocketException ex) {
    //                Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
    //        } catch (UnknownHostException ex) {
     //            Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
 //        } catch (IOException ex) {
    //            Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
    //        }

}                                         

public void createFile(String fileName) {
    String sb = "TEST CONTENT";
    JFileChooser chooser = new JFileChooser();
    chooser.setCurrentDirectory(new File("C:\\" + fileName));
    int retrieval = chooser.showSaveDialog(null);

    if (retrieval == JFileChooser.APPROVE_OPTION) {
        try {
            FileWriter fw = new FileWriter(chooser.getSelectedFile() + ".txt");
            fw.write(sb.toString());
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}

public void createServerFile() throws IOException
{
     String str = "This is a server file!";
        File newTextFile = new File("C:\\ServerFolder\\serverFile.txt");

        FileWriter fw = new FileWriter(newTextFile);
        fw.write(str);
        fw.close();
        System.out.println("\n904 - Server file created - 'serverFile.txt'");
}


private void createFileActionPerformed(java.awt.event.ActionEvent evt) {                                           
    // TODO add your handling code here:       
    createFile(username);
    notifyLbl.setText("File Created!");

    Timer timer = new Timer(5000, e -> notifyLbl.setText(""));
    timer.setRepeats(false);
    timer.start();

}                                          


private void uploadBtnActionPerformed(java.awt.event.ActionEvent evt) {                                          

    try {

        // TODO add your handling code here:
        String fileName = fileNameTxt.getText();
        String hostname = hostTxt.getText();
        String port = portTxt.getText();
        String username = usernameTxt.getText();
        String password = passwordTxt.getText();
        String text = "This is " + username + "'s file!";
        ClientHelper helper
                = new ClientHelper(hostname, port, username, password);

        File file = new File("C:\\" + username + "\\" + fileName + ".txt");
        if (!file.exists()) {
            System.out.println("File not found!");
        } else {

            String myFile = helper.writeFileAndSend(fileName, username, text);
            System.out.println("Response:\n" + "File name: " + myFile + " User: " + username);

             notifyLbl.setText("File Uploaded");

            Timer timer = new Timer(5000, e -> notifyLbl.setText(""));
            timer.setRepeats(false);
            timer.start();
        }
    } catch (SocketException ex) {
        Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
    } catch (UnknownHostException ex) {
        Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
    } catch (IOException ex) {
        Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
    }
}                                         


private void downloadBtnActionPerformed(java.awt.event.ActionEvent evt) {                                            
    try {
        // TODO add your handling code here:          
        String hostname = hostTxt.getText();
        String port = portTxt.getText();
        username = usernameTxt.getText();
        String password = passwordTxt.getText();
        String fileToDownload = downloadFileNameTxt.getText();
        String messageInFile = "User Downloaded: " + username + " *********This is a server File!**********";
        ClientHelper helper
                = new ClientHelper(hostname, port, username, password);

        File file = new File("C:\\ServerFolder\\" + fileToDownload + ".txt");
        if (!file.exists()) {
            System.out.println("File not found!");
        } else {

            helper.readFileAndSend(fileToDownload, messageInFile);
            System.out.println("\nResponse:\n" + "File name: " + fileToDownload + " User: " + username);

            notifyLbl.setText("File Downloaded");

            Timer timer = new Timer(5000, e -> notifyLbl.setText(""));
            timer.setRepeats(false);
            timer.start();
        }
    } catch (SocketException ex) {
        Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
    } catch (UnknownHostException ex) {
        Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
    } catch (IOException ex) {
        Logger.getLogger(ClientGUI.class.getName()).log(Level.SEVERE, null, ex);
    }
}                                           

public boolean validateUsername(String username) {
    username = username.trim();

    if (username == null || username.equals("")) {
        return false;
    }

    if (!username.matches("[a-zA-Z]*")) {
        return false;
    }

    return true;
}

/**
 * @param args the command line arguments
 */
public static void main(String args[]) {

    ClientGUI client = new ClientGUI(new Server());
    client.createUserFolder("DownloadedFiles");

    //client.createServerFile("serverFile");

    /* Create and display the form */
    java.awt.EventQueue.invokeLater(new Runnable() {
        public void run() {
            new ClientGUI().setVisible(true);
        }
    });
}

// Variables declaration - do not modify                     
private javax.swing.JLabel connectionLbl;
private javax.swing.JButton createFile;
private javax.swing.JButton downloadBtn;
private javax.swing.JTextField downloadFileNameTxt;
private javax.swing.JTextField fileNameTxt;
private javax.swing.JTextField hostTxt;
private javax.swing.JLabel jLabel1;
private javax.swing.JLabel jLabel2;
private javax.swing.JLabel jLabel3;
private javax.swing.JLabel jLabel4;
private javax.swing.JPanel jPanel1;
private javax.swing.JButton logOffBtn;
private javax.swing.JButton loginBtn;
private javax.swing.JLabel notifyLbl;
private javax.swing.JTextField passwordTxt;
private javax.swing.JTextField portTxt;
public javax.swing.JButton uploadBtn;
private javax.swing.JTextField usernameTxt;
// End of variables declaration

}

服务器.java

  public class Server implements ActionListener {
     JButton button = new JButton();
     public static void main(String[] args) {

    ClientGUI client = new ClientGUI();
    client.createUserFolder("ServerFolder");   

    Server server = new Server();      
    server.button = client.getButton();

    int serverPort = 7;    // default port
    if (args.length == 1) {
        serverPort = Integer.parseInt(args[0]);
    }
    try {
        // instantiates a datagram socket for both sending
        // and receiving data
        ServerDatagramSocket mySocket = new ServerDatagramSocket(serverPort);
        System.out.println("Server Ready...");          

        while (true) {  // forever loop
            //Login
            DatagramMessage request = mySocket.receiveMessageAndSender();
            System.out.println("201 - Request Received to Login");
            String message = request.getMessage();

            System.out.println("204 - Login Successful - Welcome " + message);
            // Now send the echo to the requestor
            mySocket.sendMessage(request.getAddress(),
                    request.getPort(), message);                                                                           
            //End Login


   //                 //LogOff
   //                DatagramMessage requestToLogOff = mySocket.receiveMessageAndSender();
   //                System.out.println("\n401 - Request Received to Log off");
   //                String response = requestToLogOff.getMessage();
   //
   //                System.out.println("402 - Log off Successful - Goodbye " + response);
   //                // Now send the echo to the requestor
   //                mySocket.sendMessage(request.getAddress(),
    //                        request.getPort(), response);                                                                           
     //                //End LogOff




   //                //Upload
  //                System.out.println("\n304 - Upload Requested...");             
    //                byte[] receiveData = new byte[MAX_LEN];
    //                byte[] sendData = new byte[MAX_LEN];
   //                DatagramPacket receivePacket = new DatagramPacket(receiveData, receiveData.length);
    //                mySocket.receive(receivePacket);
   //
 //                String sentence = new String(receivePacket.getData());
    //                SimpleDateFormat df = new SimpleDateFormat("EEE, MMM d, ''yy");
 //
   //                File moddedFile = new File("C:\\ServerFolder\\");
  //
 //                mySocket.sendMessage(request.getAddress(), request.getPort(), "Last upload on " + df.format(moddedFile.lastModified()));
   //                System.out.println("305 - Last upload on " + df.format(moddedFile.lastModified()));
   //                System.out.println("306 - Recieved Data: " + sentence);
    //
 //                InetAddress IPAddress = receivePacket.getAddress();
  //                int port = receivePacket.getPort();
  //                String capitalizedSentence = sentence.toUpperCase();
 //                sendData = capitalizedSentence.getBytes();
   //                DatagramPacket sendPacket
     //                        = new DatagramPacket(sendData, sendData.length, IPAddress, port);
   //                mySocket.send(sendPacket);
   //
      //                System.out.println("\n307 - File Recieved and ready for upload...");
   //                Writer writer = null;
      //
     //                String todaysDate = df.format(new Date());
 //                             
      //                writer = new BufferedWriter(new OutputStreamWriter(
    //                        new FileOutputStream("C:\\ServerFolder\\" + message.trim() + "\\" + todaysDate + ".txt"), "utf-8"));
 //                writer.write(sentence);
 //                System.out.println("308 - File upload complete!");
   //                writer.close();
     //                
  //                //End Upload  


            //Start Download
             client.createServerFile();
             System.out.println("\n504 - Download Requested..."); 
             File downloadFolder = new File("C:\\ServerFolder\\serverFile.txt");
             String myFile = null;

                 BufferedReader reader = new BufferedReader(new FileReader(downloadFolder));
                 StringBuilder sb = new StringBuilder();
                 String line = reader.readLine();                 
                 while(line != null)
                 {
                     sb.append(line);
                     sb.append(System.lineSeparator());
                     line = reader.readLine();                         
                 }     
                  myFile = sb.toString();

                 mySocket.sendMessage(request.getAddress(), request.getPort(), myFile + "\n\n501 - Download Complete");
                 //System.out.println("\n508 - Download Requested..."); 
                 JOptionPane.showMessageDialog(null, "File download complete!");  
                  System.out.println("508 - File download complete!"); 
              //End Download


        } //end while  

    } // end try       
    catch (Exception ex) {
        ex.printStackTrace();
    } // end catch     
}//end main

@Override
public void actionPerformed(ActionEvent e) {       
    if(button.getModel().isPressed())
    System.out.println("the button is pressed");
}




 } // end class

最佳答案

当您使用带有 ActionListener 参数的构造函数时，您不会调用 initComponents()，因此所有组件都不会被初始化并且全部保持为 null。所以改变这个:

public ClientGUI(ActionListener listen)
{
    uploadBtn.addActionListener(listen);
}

对此:

public ClientGUI(ActionListener listen)
{
    this(); // call the default constructor first which calls initComponents.
    uploadBtn.addActionListener(listen);
}

或者您可以直接调用 initComponents:

public ClientGUI(ActionListener listen)
{
    initComponents();
    uploadBtn.addActionListener(listen);
}

但我也不喜欢第二种解决方案，因为如果您将其他初始化代码放入默认构造函数中，则需要在两个构造函数中显式调用该代码。

关于Java - 通过 NetBeans 为另一个类中的按钮添加监听器，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/40497624/

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Java - 通过 NetBeans 为另一个类中的按钮添加监听器