java - 文本字段的 NulPointerException

Question

当我尝试获取文本字段的值并在另一个类中使用它时，我收到 NullPointer 异常..

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at gui.AddNewPasswordWindow.actionPerformed(AddNewPasswordWindow.java:86)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

这是我在单击添加按钮时遇到错误的类

public class AddNewPasswordWindow implements ActionListener{

static PasswordStorageWindow PasswordStorageWindow;

private JFrame frame;
private JTextField passwordField;
private JTextField usernameField;

public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                AddNewPasswordWindow window = new AddNewPasswordWindow(PasswordStorageWindow);
                window.frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });

}
public AddNewPasswordWindow(PasswordStorageWindow PasswordStorageWindow) {
    this.PasswordStorageWindow = PasswordStorageWindow;
    initialize();
}

private void initialize() {
    frame = new JFrame();
    frame.setAlwaysOnTop(true);
    frame.setBounds(100, 100, 240, 240);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().setLayout(null);


    JLabel lblUsername = new JLabel("Username:");
    lblUsername.setFont(new Font("Tahoma", Font.PLAIN, 14));
    lblUsername.setBounds(10, 11, 204, 20);
    frame.getContentPane().add(lblUsername);

    JLabel lblPassword = new JLabel("Password:");
    lblPassword.setFont(new Font("Tahoma", Font.PLAIN, 14));
    lblPassword.setBounds(10, 81, 143, 20);
    frame.getContentPane().add(lblPassword);

    JButton btnAdd = new JButton("ADD");
    btnAdd.setBounds(64, 160, 89, 23);
    frame.getContentPane().add(btnAdd);
    btnAdd.addActionListener(this);
    btnAdd.setActionCommand("add");

    JButton btnGenerate = new JButton("Generate");
    btnGenerate.setBounds(125, 82, 89, 23);
    frame.getContentPane().add(btnGenerate);
    btnGenerate.addActionListener(this);
    btnGenerate.setActionCommand("generate");

    usernameField = new JTextField();
    usernameField.setBounds(30, 42, 184, 20);
    frame.getContentPane().add(usernameField);
    usernameField.setColumns(10);


    passwordField = new JTextField();
    passwordField.setBounds(30, 116, 184, 20);
    frame.getContentPane().add(passwordField);
    passwordField.setColumns(10);

}

public void actionPerformed(ActionEvent e) {
    if("generate".equals(e.getActionCommand())){
        Random generator = new Random();
        passwordField.setText(generator.toString());
    }
    if("add".equals(e.getActionCommand())){
        String username = usernameField.getText();
        String password = passwordField.getText();
        PasswordStorageWindow.getUsername(username);
        PasswordStorageWindow.getPassword(password);
        }
    }
}

这是我想要存储和显示文本框的值的类...

public class PasswordStorageWindow implements ActionListener{

private JFrame frmExistingPassword;
private JTable table;
public ArrayList<String> data1;
String username = LoginWindow.Username();

public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                PasswordStorageWindow PasswordStorageWindow = new PasswordStorageWindow();
                PasswordStorageWindow.frmExistingPassword.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}
public void getUsername(String username){
    data1.add(username);
}
public void getPassword(String password){
    data1.add(password);
}

public PasswordStorageWindow() throws FileNotFoundException {
    initialize();
}

private void initialize() throws FileNotFoundException {
    String[] columnNames = {"Site", "Password"};
    File f = new File("D:\\Programming\\Projects\\Workspace\\Password Storage v1.1\\usernames\\" + username + "\\" + username + ".pass.txt");
    Scanner scan = new Scanner(f);
    data1 = new ArrayList<String>();
    while (scan.hasNextLine())
    {

        data1.add(scan.nextLine());
    }
    Object[][] data = new Object[data1.size()/2+1][2];
    data[0][0] = "Site";
    data[0][1] = "Password";
    int counter = 1;
    for (int i = 0; i < data1.size(); i+=2){
        data[counter][0] = data1.get(i);
        data[counter][1] = data1.get(i+1);
        counter++;
    }

    frmExistingPassword = new JFrame();
    frmExistingPassword.setTitle("Existing Passwords");
    frmExistingPassword.setBounds(100, 100, 560, 600);
    frmExistingPassword.setResizable(false);
    frmExistingPassword.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frmExistingPassword.getContentPane().setLayout(null);

    ImageIcon add = new ImageIcon("add.png");
    ImageIcon delete = new ImageIcon("delete.png");

    JButton buttonAdd = new JButton("ADD", add);
    buttonAdd.setBounds(162, 4, 180, 75);
    frmExistingPassword.getContentPane().add(buttonAdd);
    buttonAdd.setActionCommand("add");


    JButton buttonDelete = new JButton("Delete password", delete);
    buttonDelete.setBounds(360, 4, 180, 75);
    frmExistingPassword.getContentPane().add(buttonDelete);
    buttonDelete.setActionCommand("delete");

    JButton buttonBack = new JButton("Go back");
    buttonBack.setBounds(5, 4, 140, 75);
    frmExistingPassword.getContentPane().add(buttonBack);
    buttonBack.setActionCommand("back");
    table = new JTable(data, columnNames)
    {
        public boolean isCellEditable(int row, int col)
        {
            return false;
        }
    };
    table.setBounds(2, 106, 542, 455);
    frmExistingPassword.getContentPane().add(table);
    table.setPreferredScrollableViewportSize(new Dimension(520, 500));
    table.setFillsViewportHeight(true);

    buttonAdd.addActionListener(this);
    buttonDelete.addActionListener(this);
    buttonBack.addActionListener(this);
}

public void actionPerformed(ActionEvent e) {
    if("back".equals(e.getActionCommand())){
        MainMenuWindow.main(null);
        frmExistingPassword.dispose();
    }
    if("add".equals(e.getActionCommand())){
        File file = new File("D:\\Programming\\Projects\\Workspace\\Password Storage v1.1\\usernames\\" + username + "\\" + username + ".pass.txt");
        if(!file.exists())
        {
        try {
            PrintWriter out = new PrintWriter(file);
            out.close();
        } catch (FileNotFoundException e1) {}
        }
        AddNewPasswordWindow newWindow = new AddNewPasswordWindow(null);
            AddNewPasswordWindow.main(null);
            }
                try
                {
                    PrintWriter out = new PrintWriter("D:\\Programming\\Projects\\Workspace\\Password Storage v1.1\\usernames\\" + username + "\\" + username + ".pass.txt");
                    for (int i = 0; i<data1.size(); i++)
                    {
                        out.println(data1.get(i));
                    }
                    out.close();
                    PasswordStorageWindow frmExistingPassword1 = new PasswordStorageWindow();
                    frmExistingPassword1.main(null);
                    frmExistingPassword.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
                    frmExistingPassword.setVisible(false);
                } catch (Exception e1)
                {
                    System.out.println("Error writing new file/saving changes...!");
                }
            }
        }

Answer 1

如果你不告诉我们你的第 86 行在哪里，在我看来，你从未初始化 PasswordStorageWindow。

你有:

static PasswordStorageWindow PasswordStorageWindow; // Not initialized anywhere

private JFrame frame;
private JTextField passwordField;
private JTextField usernameField;

public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                // You are passing a null value here, PasswordStorageWindow is not initialized.
                AddNewPasswordWindow window = new AddNewPasswordWindow(PasswordStorageWindow); 
                window.frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

检查代码中的注释。

顺便说一句，您应该遵循 java 约定并使用驼峰命名法，变量和方法名称应以小写字母开头。