显示用户名

Question

public class Login extends javax.swing.JFrame {
public static String user;

user = txt_user.getText();

public Home() {
    initComponents();
    date();
    time();

    Login l = new Login();
    lbl_user.setText(l.user);

public getuser(){
String u = txt_user.getText();
return;
}

Answer 1

学习手动编写UI代码是非常值得的，它将使您更容易了解何时使用表单编辑器以及如何最大限度地利用它们。

您应该将转储到用户上的窗口数量限制为一个活动窗口，并使用对话框向用户显示或提示更多信息。有关更多详细信息，请参见如何创建对话框

JFrame不是一个阻塞窗口，也就是说，当您使其可见时，代码将继续执行，这意味着，在您的情况下，您显示了登录窗口，但在尝试设置标签的文本之前，用户还没有时间输入任何内容...

LoginPanel loginPane = new LoginPanel();
// This will wait here until the dialog is closed for some reason...
int result = JOptionPane.showConfirmDialog(this, loginPane, "Login", JOptionPane.OK_CANCEL_OPTION, JOptionPane.PLAIN_MESSAGE);
// Then you can determine what you want to do in response to the
// closing of the dialog
if (result == JOptionPane.OK_OPTION) {
    label.setText("Welcome " + loginPane.getUsername());
}

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JPasswordField;
import javax.swing.JTextField;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {

            setLayout(new GridBagLayout());
            JLabel label = new JLabel("Unknown user");
            add(label);

            LoginPanel loginPane = new LoginPanel();
            int result = JOptionPane.showConfirmDialog(this, loginPane, "Login", JOptionPane.OK_CANCEL_OPTION, JOptionPane.PLAIN_MESSAGE);
            if (result == JOptionPane.OK_OPTION) {
                label.setText("Welcome " + loginPane.getUsername());
            }

        }

    }

    public class LoginPanel extends JPanel {

        private JTextField userName;
        private JPasswordField password;

        public LoginPanel() {
            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridx = 0;
            gbc.gridy = 0;
            gbc.anchor = GridBagConstraints.WEST;

            add(new JLabel("Username: "), gbc);
            gbc.gridy++;
            add(new JLabel("Password: "), gbc);

            gbc.gridx++;
            gbc.gridy = 0;
            gbc.anchor = GridBagConstraints.EAST;

            userName = new JTextField(20);
            password = new JPasswordField(20);

            add(userName, gbc);
            gbc.gridy++;
            add(password, gbc);
        }

        public String getUsername() {
            return userName.getText();
        }

        public char[] getPassword() {
            return password.getPassword();
        }

    }

}