如何阻止用户在Netbeans v8上的弹出窗口中输入数字

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JTextField;

public class PopupWindowExample {
    public static void main(String[] args) {
        JFrame frame = new JFrame("Popup Window Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
        JTextField textField = new JTextField(10);
        JButton button = new JButton("Submit");
        
        button.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                String input = textField.getText();
                
                // 验证输入是否为数字
                if (input.matches("\\d+")) {
                    JOptionPane.showMessageDialog(frame, "输入无效！请不要输入数字。");
                } else {
                    JOptionPane.showMessageDialog(frame, "输入有效！");
                }
            }
        });
        
        frame.getContentPane().add(textField);
        frame.getContentPane().add(button);
        frame.pack();
        frame.setVisible(true);
    }
}