package outSide;
import java.awt.Color;
import java.awt.Container;
import java.awt.Graphics;

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

@SuppressWarnings("serial")
public class JFrameTest2 extends JFrame{
        public static JFrame jj;
        public static void main(String[] args) {
            jj=new JFrameTest2();
        }
        Graphics gra;
        JButton button;
        public JFrameTest2() {
            try{
                //窗口
                this.setTitle("Control");
                this.setBounds(1100,100,700,800);
                this.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
                this.setVisible(true);
                JPanel panel = new JPanel();  
                JTextArea textArea = new JTextArea();    
                panel.setLayout(new GridLayout());  
                textArea.setText("test");  
                this.add(panel);  
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
}

<- 如果问题得到解决，请点我回答左上角的采纳和向上的箭头，谢谢

panel.add(textArea);
要加这个，否则文本框不会显示。