I am having trouble implementing ActionListener to make an existing lab's buttons interactive. Here is the error I am getting: Exception in thread "main" java.lang.ExceptionInInitializerError

at ControlPanel.(ControlPanel.java:16)

at MainFrame.(MainFrame.java:12)

at app.main(app.java:11)

Caused by: java.lang.RuntimeException: Uncompilable source code - CenterPanel is not abstract and does not override abstract method actionPerformed(java.awt.event.ActionEvent) in java.awt.event.ActionListener

at CenterPanel.(CenterPanel.java:7)

... 3 more

I am trying to use my existing code from prior labs as well as follow the example given by my professor, but I can't figure out what the issue is.

Here is my code:

app.java

public class app {

public static void main(String args[]) {

student st1 = new student("Student", "One", 30);

student st2 = new student("Etudiant", "Two", 25);

student st3 = new student("Student", "Wagner", 28);

student st4 = new student("Jeff", "Goldblum", 66);

group gp = new group("Nittany Lions", st1, st2, st3, st4);

MainFrame mjf = new MainFrame(gp);

}

}

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group.java

public class group {

String name;

student st1;

student st2;

student st3;

student st4;

group(String g1, student st1, student st2, student st3, student st4) {

this.name = g1;

this.st1 = st1;

this.st2 = st2;

this.st3 = st3;

this.st4 = st4;

}

String getInfo() {

return name;

}

double groupGPA() {

double avgGPA = (st1.gpa + st2.gpa + st3.gpa + st4.gpa) / 4;

return avgGPA;

}

}

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student.java

public class student {

String fName;

String lName;

int age;

double gpa;

student(String fName, String lName, int age) {

this.fName = fName;

this.lName = lName;

this.age = age;

this.gpa = semesterGPA();

}

String getName() {

return fName + " " + lName;

}

double semesterGPA() {

double sgpa = Math.random() * 4.0;

return sgpa;

}

}

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TopPanel.java

import java.awt.*;

import javax.swing.*;

public class TopPanel extends JPanel {

JButton jb1, jb2, jb3;

String jb3s;

public TopPanel(group group) {

super();

setBackground(Color.blue);

jb1 = new JButton(group.getInfo());

jb2 = new JButton("Group AVG GPA is");

jb3 = new JButton(String.format("%.2f", group.groupGPA()));

add(jb1);

add(jb2);

add(jb3);

}

}

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MainFrame.java

import java.awt.*;

import javax.swing.*;

import static javax.swing.JFrame.EXIT_ON_CLOSE;

public class MainFrame extends JFrame {

ControlPanel mjp;

public MainFrame(group group) {

super("Sample Lab");

mjp = new ControlPanel(group);

getContentPane().add(mjp, "Center");

setDefaultCloseOperation(EXIT_ON_CLOSE);

setSize(800, 480);

setVisible(true);

}

}

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ControlPanel.java

import java.awt.*;

import javax.swing.*;

public class ControlPanel extends JPanel {

CenterPanel cp;

TopPanel tp;

public ControlPanel(group group) {

super();

BorderLayout border = new BorderLayout();

setLayout(border);

setBackground(Color.gray);

tp = new TopPanel(group);

cp = new CenterPanel(group);

add(tp, "North");

add(cp, "Center");

}

}

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CenterPanel.java

import java.awt.*;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import javax.swing.*;

public class CenterPanel extends JPanel implements ActionListener {

JButton jb1, jb2, jb3, jb4;

public CenterPanel(group group) {

super();

GridLayout grid = new GridLayout(4, 1);

setLayout(grid);

setBackground(Color.pink);

jb1 = new JButton("NAME = " + group.st1.getName() + "|GPA = "

+ String.format("%.2f", group.st1.gpa));

add(jb1);

jb2 = new JButton("NAME = " + group.st2.getName() + "|GPA = "

+ String.format("%.2f", group.st2.gpa));

add(jb2);

jb3 = new JButton("NAME = " + group.st3.getName() + "|GPA = "

+ String.format("%.2f", group.st3.gpa));

add(jb3);

jb4 = new JButton("NAME = " + group.st4.getName() + "|GPA = "

+ String.format("%.2f", group.st4.gpa));

add(jb4);

jb1.addActionListener(this);

jb2.addActionListener(this);

jb3.addActionListener(this);

jb4.addActionListener(this);

@Override

public void actionPerformed

(ActionEvent event

)

{

if (event.getSource() == jb1) {

jb1.setText(g1.sd1.getName() + " " + g1.sd1.getGPA());

tp.jb3.setText(g1.averageGPA());

}

if (event.getSource() == jb2) {

jb2.setText(g1.sd2.getName() + " " + g1.sd2.getGPA());

tp.jb3.setText(g1.averageGPA());

}

if (event.getSource() == jb3) {

jb3.setText(g1.sd3.getName() + " " + g1.sd3.getGPA());

tp.jb3.setText(g1.averageGPA());

}

if (event.getSource() == jb4) {

jb4.setText(g1.sd4.getName() + " " + g1.sd4.getGPA());

tp.jb3.setText(g1.averageGPA());

}

}

}

The new requirement of the lab is that you implement the ActionListener in ControlPanel, which is the panel that contains the other two panels.

You have to use the traditional model for listening that you have been using so far: public class ControlPanel extends JPanel implements ActionListener

Thank you for your help!