You need to move your actionPerformed
declaration outside of your constructor.
Currently you have this:
public class GUI extends JFrame implements ActionListener {
...
public GUI() {
...
public void actionPerformed(ActionEvent event) {
...
}
}
}
It needs to be like:
public class GUI extends JFrame implements ActionListener {
...
public GUI() {
...
}
public void actionPerformed(ActionEvent event) {
...
}
}
I have not tested your code but that is the first obvious problem.