Java应用程序: Getting input before running

Question

public class checkUsernames extends JFrame {
private static JTextArea textArea1;
private static JButton button1;
private static JScrollPane scrollPane1;
private static JTextField textField1;
private static JPasswordField passwordField1;
private static JLabel label3;
private static JButton button2;
private static JLabel label1;
private static JLabel label2;

public checkUsernames() {
    initComponents();
}

public static void main(String[] args) throws IOException {
        try {
            UIManager.setLookAndFeel("com.sun.java.swing.plaf.nimbus.NimbusLookAndFeel");
        } catch (Exception e) {
            JOptionPane.showMessageDialog(null, "Nimbus isn't available");
        }

        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                checkUsernames GUI = new checkUsernames();
                GUI.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                GUI.setVisible(true);
            }
        });
        String username = textField1.toString();
        String password = passwordField1.toString();

线程“main”中的异常 java.lang.NullPointerException

checkUsernames 是唯一的类。当我尝试运行应用程序时，程序将进一步执行(无需字符串用户名和字符串密码即可继续)，而无需等待输入。我该如何解决这个问题？

Answer 1

如果您希望代码执行在等待输入时停止，请将 JFrame 设为模态 JDialog 或 JOptionPane。