How does this work here?

Question

Java

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

public class SimpleGuilB implements ActionListener {
    JButton button;
    public static void main(String [] args){
        SimpleGuilB gui = new SimpleGuilB();
        gui.go();

    }
    public void go(){
        JFrame frame = new JFrame();
        button = new JButton("click me");

        button.addActionListener(this); //ЧТО ЗДЕСЬ ДЕЛАЕТ THIS?

        frame.getContentPane().add(button);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(100,300);
        frame.setVisible(true);
    }
    public void actionPerformed(ActionEvent event){
       button.setText("I ve been clicked");
        System.out.println("fjgji");
    }

}

Answer 1

POINTS TO AN INSTANCE OF AN ENCOUNTERING CLASS!

Answer 2

You have created the SimpleGuilB class and implemented the ActionListener interface into it, which tells you to implement the actionPerformed() method.
Further in your SimpleGuilB class you say button.addActionListener() i.e. you tell the button where the events from the button should be passed and as an argument you tell this. This says that, roughly speaking, "I \ me" i.e. it was this created instance of the SimpleGuilB class that implemented the ActionListener .
Those. simply put, this inside the class says that it is "I\me\mine\mine" of the instance.
Otherwise, you could create an ActionListener implementation like this

public class SimpleGuilB{ 
... код
public void go(){
...
button.addActionListener(new ButLister()); 
}
}

public class ButLister implements ActionListener{
public void actionPerformed(ActionEvent event){
        System.out.println("fjgji");
    }
}