// Submit Button Listener
            submitButton.addActionListener(new ActionListener(){
                public void actionPerformed(ActionEvent ae){
                    boolean notDuplicated = false;

                    String id = studentIDField.getText();
                    String username = userNameField.getText();
                    String password = passwordField.getText();

                    boolean idValid = id.matches("\\d{5,6}");
                    boolean usernameValid = username.matches("[A-Za-z][A-Za-z0-9]*@[A-Za-z][A-Za-z0-9]*\\.(com|edu|org)");
                    boolean passwordValid = password.matches("^(?=.*[a-z])(?=.*[A-Z])(?=.*[0-9])(?=.*[~!#$])[A-Za-z0-9~!#$]{8,}$");

                    for (Student student : studentsList) {
                        if (username.equals(student.getUsername())) {
                            notDuplicated = true;
                        }
                    }

                    if (notDuplicated) {
                        JOptionPane.showMessageDialog(rootPane, "Username already taken!");
                        userNameField.setText("");
                    }

                    if (!idValid) {
                        JOptionPane.showMessageDialog(rootPane, "Please enter a valid user ID!");
                        studentIDField.setText("");
                    }

                    if (!usernameValid) {
                        JOptionPane.showMessageDialog(rootPane, "Please enter a valid username!");
                        userNameField.setText("");
                    }

                    if (!passwordValid) {
                        JOptionPane.showMessageDialog(rootPane, "Please enter a valid password!");;
                        passwordField.setText("");
                    }

                    if (notDuplicated == false && idValid == true && usernameValid == true && passwordValid == true) {
                        for (Student student : studentsList) {
                            if (id == student.getId()) {
                                student.setUsername(username);
                                student.setPassword(password);
                            }
                        }
                        JOptionPane.showMessageDialog(rootPane, "Student account added!");
                        studentIDField.setText("");
                        userNameField.setText("");
                        passwordField.setText("");
                    }
                }
            });