Question

我无法获取我在Jtextfield中输入的信息，从这个类到主类，我只是得到null

public class FirstWindow extends JFrame {

    private static final long serialVersionUID = 1L;
    private static final String TEXT_FIELD = "text field";
    private static final String TEXT2_FIELD = "text field";
    private static final String PASS_FIELD = "pass field";

    private String loginname;
    private String loginlname;
    private String loginpass;

    public FirstWindow() {
        super("login");
        setSize(375, 125);
        setResizable(false);
        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        final JTextField textField = new JTextField(10);// information inputs
        final JTextField textField2 = new JTextField(10);// information inputs
        final JPasswordField passwordField = new JPasswordField(10);// information
                                                                    // inputs

        JPanel p = new JPanel(new GridBagLayout());
        JPanel p1 = new JPanel();
        JPanel p2 = new JPanel(new GridBagLayout());

        GridBagConstraints gbc = new GridBagConstraints();
        gbc.insets = new Insets(5, 5, 5, 5);

        JButton showNamePasswordBtn = new JButton("Ok");
        showNamePasswordBtn.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent arg0) {
                loginname = textField.getText();// setting first value
                loginlname = textField2.getText();// setting sc value
                loginpass = new String(passwordField.getPassword());// setting
                                                                    // th value
                // System.out.println ("vardas  " +loginname);//information
                // holders works on this class
                // System.out.println ("varda  " +loginlname);
                // System.out.println ("vard  " +loginpass);
                System.exit(0);
            }
        });

        JLabel label = new JLabel("Vartotojo Vardas   ");
        JLabel label2 = new JLabel("Vartotojo Pavarde");
        JLabel label3 = new JLabel("   Vartotojo Slaptazodis");

        gbc.gridx = 0;
        gbc.gridy = 0;
        p.add(label, gbc);
        gbc.gridx = 1;
        gbc.gridy = 0;
        p.add(label2, gbc);
        gbc.gridx = 2;
        gbc.gridy = 0;
        p.add(label3, gbc);

        p1.add(textField, TEXT_FIELD);
        p1.add(textField2, TEXT2_FIELD);
        p1.add(passwordField, PASS_FIELD);

        p2.add(showNamePasswordBtn);

        add(p2, BorderLayout.SOUTH);
        add(p1, BorderLayout.CENTER);
        add(p, BorderLayout.NORTH);
    }

    public String back() { // tried getting back info
        return loginname;
    }// val1

    public String back1() {
        return loginlname;
    }// val2

    public String back2() {
        return loginpass;// val3
    }
}

这是我想要获取我的信息的主要课程

public class GUImain {

    public static void main(String[] args) throws Exception {
        FirstWindow fw = new FirstWindow();
        fw.setVisible(true);
        String a, b, c;// creating strings
        a = fw.back();// setting val
        b = fw.back1();// setting val
        c = fw.back2();// setting val
        System.out.println("vardas  " + a);
        System.out.println("pavard  " + b);
        System.out.println("pass " + c);
    }
}

所以主要的问题是所有id工作正常，期望我无法从Jframe类中获取任何最重要的信息

Answer 1

运行此代码时，main()方法会执行。它构建了您想要的GUI，您可以根据需要检索信息。例如：textField.getText();

但是当main()方法执行时，TextField全部为空，因此返回null。您键入的值仅在您单击按钮时存储在变量中，因为您在其上添加了侦听器。点击按钮后，尝试输出后的值。

要查看它：首先从侦听器中移除此行：System.exit(0);（停止您的程序），并将其添加到main()，以查看您可以从fw.back()获取值在你的主要班级：

while(fw.back() == null){} System.out.println(fw.back());

您将看到值

无法从Jframe子类获取正常主类的信息

1 个答案: