JFrame周围的LineBorder消失了

Question

我正在尝试让JPanel持有JTextArea。我希望JPanel自己调整大小以匹配JTextArea的preferredSize，因为这是显示所有文本所需的大小。最后，我想在JTextArea和Jpanel之间放置一个空边框，但我在示例代码中省略了它。

我还希望JPanel周围有一个线条边框。下面的代码在某些时候有效，但偶尔lineBorder的底部和右侧部分会消失。为什么会这样？附：我知道我更新尺寸的方式不是很优雅。有没有更好的办法？

这是代码：

import javax.swing.*;
import javax.swing.border.Border;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import java.awt.*;

public class TextThoughtView extends JPanel {
    private JTextArea myTextArea;

    TextThoughtView(){
        //configure the View
        setBackground(new Color(0, 0, 0, 0));
        setLayout(new BorderLayout());
        myTextArea = new JTextArea();
        add(myTextArea,BorderLayout.CENTER);

        //configure the border
        Border border = BorderFactory.createLineBorder(new Color(150,150,150));
        setBorder(border);

        //configure the textArea
        Font font = new Font("Monospaced", Font.BOLD, 12);
        myTextArea.setFont(font);
        myTextArea.setBackground(new Color(50, 50, 50)); //same as the color of the canvas.
        myTextArea.setForeground(new Color(255, 255, 255)); //sets the text color
        //myTextArea.setBorder(new EmptyBorder(new Insets(5,5,5,5)));
        myTextArea.getDocument().addDocumentListener(new MyDocumentListener()); //add a listener for text changes
        myTextArea.setSize(new Dimension(10,20));

        //sync this's size with the textArea
        sizeToFitTextArea();

    }
    //accessors
    private void sizeToFitTextArea(){
        setSize(myTextArea.getPreferredSize().width,myTextArea.getPreferredSize().height);
    }
    private class MyDocumentListener implements DocumentListener {
        public void insertUpdate(DocumentEvent e) {
            sizeToFitTextArea();
        }
        public void removeUpdate(DocumentEvent e) {
            sizeToFitTextArea();
        }
        public void changedUpdate(DocumentEvent e) {
            //Plain text components do not fire these events
        }
    }
    public static void main(String args[]){
        JFrame myFrame = new JFrame();
        myFrame.setLayout(new BorderLayout());
        myFrame.setSize(new Dimension(400,300));

        JPanel myPanel = new JPanel();
        myPanel.add(new TextThoughtView());
        myPanel.setBackground(new Color(50,50,50));
        myFrame.add(myPanel,BorderLayout.CENTER);
        myFrame.setVisible(true);
     }
}