面板之间的通信Java

Question

我在完成家庭作业时遇到了很多麻烦。我们获得了三个JPanel：myJPanel，myJPanel1和myJPanel2。我必须在mJPanel1中有一个JButton，在myJPanel2中更新按钮b2的文本。问题是我无法对myJPanel2进行任何更改。我尝试的一切都给了我一个NullPointerException。请帮忙。

这是代码： myJPanel -

import java.awt.*;
import javax.swing.*;
public class MyJPanel extends JPanel {
    MyJPanel panel;
    public MyJPanel() {
        super();
        setBackground(Color.gray);
        setLayout(new BorderLayout());
        MyJPanel2 p2 = new MyJPanel2();
        add(p2, "Center");
        MyJPanel1 p1 = new MyJPanel1(p2);
        add(p1, "North");
    }
}

myJPanel1 -

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class MyJPanel1 extends JPanel implements ActionListener {
    JButton jl1;
    Student st1 = new Student("Fred", "Fonseca", 44);
    myJPanel panel;
    myJPanel2 panel2;
    public MyJPanel1(JPanel p2) {
        super();
        setBackground(Color.yellow);
        // the whatsUp of this student has to shown in the other panel
       jl1 = new JButton(st1.getInfo());
       jl1.addActionListener(this);
       add(jl1);
    }@
    Override
    public void actionPerformed(ActionEvent event) {
        Object obj = event.getSource();
        if (obj.equals(jl1)) {
            panel2.b2.setText("test"); //This is where the NullPointerException is...
        }
    }
}

myJPanel2 -

import java.awt.*;
import javax.swing.*;
public class myJPanel2 extends JPanel {
    //==================================================
    //no changes allowed in myJPanel2 for assignment 05
    //==================================================
    JButton b1, b2, b3, b4;
    public myJPanel2() {
        super();
        setBackground(Color.pink);
        //setLayout(new GridLayout(3,1));
        b1 = new JButton("When the user clicks on the button in the UPPER panel");
        add(b1);
        b2 = new JButton("Display here whatsUp from the student in UPPER Panel");
        add(b2);
        b3 = new JButton("===>>>>You CANNOT create a student here <======");
        add(b3);
        b4 = new JButton("It has to be the student from the UPPER Panel");
        add(b4);
    }
}

非常感谢任何帮助。几天来我一直坚持这个问题。