如何去除JTextField边缘的模糊？

import javax.swing.*;
import javax.swing.border.Border;
import java.awt.*;

public class TextFieldExample {
    public static void main(String[] args) {
        JFrame frame = new JFrame("TextField Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300, 200);

        JPanel panel = new JPanel();
        panel.setLayout(new FlowLayout());

        JTextField textField = new JTextField(20);
        Border border = BorderFactory.createLineBorder(Color.BLACK); // 创建自定义边框
        textField.setBorder(border); // 设置边框
        textField.setMargin(new Insets(0, 0, 0, 0)); // 设置内边距为零

        panel.add(textField);
        frame.add(panel);
        frame.setVisible(true);
    }
}