关于#JAVA#的问题，如何解决？

Question

题目就是做出来这个界面，但是我代码运行窗口没有任何内容，谁能帮我看看谢谢

```java
import javax.swing.*;
import java.awt.*;

class Demo6__1 extends JFrame {
    JPanel j1 = new JPanel();
//    JPanel j2 = new JPanel();
    JButton btn10 = new JButton("."); JButton btn11 = new JButton("-");
    JTextField txt1 ;
    public void Jtxt(){
        txt1 = new JTextField(10);
        j1.add(txt1);
    }


    public void Jbtn(){
        JButton a[] = new JButton[10];

        for (int i = 0;i<=9;i++){//循环添加按钮
            a[i] = new JButton(String.valueOf(i));
            j1.add(a[i]);
        }
        j1.add(btn10);
        j1.add(btn11);
    }

    public void Display(){
        setVisible(true);
        setResizable(true);
        setSize(600,600);
        j1.setLayout(new FlowLayout());
//        j2.setLayout(new FlowLayout());
        Jtxt();
        Jbtn();
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    }

}

public class Demo6_1 {
    public static void main(String[] args) {
        new Demo6__1().Display();
    }
}

Answer 1

看这个
https://blog.csdn.net/qq_43803536/article/details/124386564