java Swing 加入一个滚动条后不出东西了，为什么

Question

为什么我的hello content不显示了public class Loading extends JDialog{
private static final long serialVersionUID = 1L;

private JPanel textPanel;
private JPanel inButPanel;
private JTextArea jtaTitle;
private JScrollPane jspContent;
private JTextArea jtaContent;
private JButton jbtPre;
private JButton jbtNext;
private JButton jbtSave;
private String titleNum="(1) ";
public Loading(JFrame jf){
super(jf,true);
setBounds(400,100,400,600);
setLayout(new BorderLayout());

textPanel=new JPanel();
textPanel.setLayout(null);

jtaTitle=new JTextArea("hello title");
jtaTitle.setLineWrap(true);
jtaTitle.setEditable(false);
jtaTitle.setText(titleNum+jtaTitle.getText());
jtaTitle.setBounds(0,0,400,60);
jtaTitle.setFont(new Font("Arial",Font.PLAIN,14));
textPanel.add(jtaTitle,BorderLayout.NORTH); jtaContent=new JTextArea();
jtaContent.setText("hell content");
jspContent=new JScrollPane();
jspContent.setBounds(0,60,390,470);
jspContent.add(jtaContent);
textPanel.add(jspContent);

inButPanel=new JPanel();
jbtPre=new JButton("上一篇");
jbtNext=new JButton("下一篇");
jbtSave=new JButton("保存");
inButPanel.add(jbtPre);
inButPanel.add(jbtNext);
inButPanel.add(jbtSave);
inButPanel.setBounds(0,530,400,70);
textPanel.add(inButPanel,BorderLayout.SOUTH);

add(textPanel,BorderLayout.CENTER);
setTitle("段落验证");
setVisible(true);
setBackground(new Color(Integer.decode("#f5f6f0")));
}

public static void main(String[] args) {
new Loading(null);
}
}

Answer 1

jspContent.add(jtaContent);
此处不是用add，而应该是用setViewportViewjspContent.setViewportView(jtaContent);

Answer 2

或者直接这样
        jtaContent=new JTextArea();
        jtaContent.setText("hell content");
        jspContent=new JScrollPane(jtaContent);
        jspContent.setBounds(0,60,390,470);
        //jspContent.add(jtaContent);new的时候直接以文本框为基础生成，不需要再往上加
        textPanel.add(jspContent);