这个程序怎么改改

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

public class Smain extends JFrame implements ActionListener {
      private JLabel Top;
      private JButton find;
      private JButton add;
      private JButton modify;
      private JButton delete;
      private JPanel tp;
      private JPanel panel1;
      private JPanel panel2;
     
      
      public Smain(){
          super("主界面");
          Container container=getContentPane();
          container.setLayout(new BorderLayout(8,8));
          this.setBackground(Color.RED);
          this.setBounds(400,200,500,500); //大小与位置；
          
          
          Top = new JLabel("学生信息管理系统",SwingConstants.CENTER);
          tp= new JPanel();
          tp.setBackground(Color.yellow);
          tp.add(Top);
          
          find= new JButton("find");
          find.addActionListener(this);//find 按钮进行事件监听；
          add= new JButton("add");
          add.addActionListener(this);//add 按钮进行事件监听；
          modify= new JButton("modify");
          modify.addActionListener(this);//modify 按钮进行事件监听；
          delete= new JButton("delte");
          delete.addActionListener(this);//delete 按钮进行事件监听；
           
          panel1=new JPanel();
          panel1.setBackground(Color.yellow);
          panel1.add(find);
          panel1.add(add);
          panel1.add(modify);
          panel1.add(delete);  //添加按钮到panel1面板；
          
          panel2= new JPanel();
        
        
          panel2.setBackground(Color.white);
          container.add(BorderLayout.NORTH,tp);
          
          container.add(panel2,BorderLayout.CENTER);
          container.add(panel1,BorderLayout.SOUTH);
        pack();
          this.setVisible(true);
      }

      public void actionPerformed(ActionEvent event){
           JLabel jt= new JLabel("hello",SwingConstants.CENTER);
             
          if (event.getSource()==find){
              
              
               
              panel2.add(jt);
                  
              //container.add(panel2,BorderLayout.CENTER);
              //JOptionPane.showMessageDialog(null,"hello" );
              
          }
           else if(event.getSource()==modify){}
            
          
          
            else if(event.getSource()==add ){}
          
           
            else if(event.getSource()==delete){}
          
          
          
           
      }
    public static void main(String[] args) {
       Smain smain= new Smain();
       smain.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
       

    }

}
为什么执行后点击 add按钮后,窗体不会立即显示出 hello 标签 ,怎么改才能立即显示出来呢~大虾指教~~~

container.add(BorderLayout.NORTH,tp);

里面的参数顺序对吗 ？？

这个简单 我以前也遇到过 很郁闷
if (event.getSource()==find){               
              panel2.add(jt);                  
             validate();              }

谢了,搞定