Крестики-Нолики

import javax.swing.*;
 
import java.awt.*;
import java.awt.event.*;
 
public class my4 {
 
    public static void main(String[] args) {
        MyFrame frame = new MyFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}
 
class MyFrame extends JFrame{
    
    JButton b[] = new JButton[9];
    String a1,a2,a3,b1,b2,b3,c1,c2,c3;
    String s[] = {a1,a2,a3,b1,b2,b3,c1,c2,c3};
    String znak;
    
    int player = 0;
    
    public MyFrame(){
    setTitle("TicTacToe");
    setSize(500,500);
    Container c = getContentPane();
    c.setLayout(new GridLayout(3,3));
    
    for(int i=0;i<b.length;i++){
         b[i] = new JButton(s[i]);
         b[i].setText(s[i]);
         b[i].addMouseListener(new MouseAdapter(){
             public void mouseClicked(MouseEvent e){
                
                player ++;                       //
                if(player > 1) player = 0;       //Определение игрока
                  System.out.println(player);    //
                
                if(player == 0) {znak ="x"; b[i].setText(znak);}  //  Здесь ошибка
                if(player == 1) {znak = "o"; b[i].setText(znak);}     //
                System.out.println(znak);
             }
         });
         c.add(b[i]);
        }
 }
}

b[i]

package def;
 
import java.awt.Container;
import java.awt.GridLayout;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
 
import javax.swing.JButton;
import javax.swing.JFrame;
 
public class my4 {
 
    public static void main(String[] args) {
        Player firstPlayer = new Player("Mike", "O");
        Player secondPlayer = new Player("Ваня", "X");
        Listener gameplay = new Listener(firstPlayer, secondPlayer);
        MyFrame frame = new MyFrame(gameplay);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}
 
class MyFrame extends JFrame {
    public MyFrame(Listener gameplay) {
        setTitle("TicTacToe");
        setSize(500, 500);
        Container c = getContentPane();
        c.setLayout(new GridLayout(3, 3));
 
        for (int i = 0; i < 9; i++) {
            JButton b = new JButton();
            b.addMouseListener(gameplay);
            c.add(b);
        }
    }
}
 
class Listener extends MouseAdapter {
    private int actions = 0;
    private boolean isFirstPlayer = true;
    Player firstPlayer;
    Player secondPlayer;
 
    public Listener(Player firstPlayer, Player secondPlayer) {
        this.firstPlayer = firstPlayer;
        this.secondPlayer = secondPlayer;
    }
 
    public void mouseClicked(MouseEvent e) {
        JButton pressedBtn = (JButton) e.getSource();
        if (actions > 8) {
            return;
        }
        if (!pressedBtn.isEnabled()) {
            System.out.println("Invalid turn");
            return;
        }
        if (isFirstPlayer) {
            System.out.println("turn of " + firstPlayer.name);
            pressedBtn.setText(firstPlayer.znak);
        } else {
            System.out.println(secondPlayer.name + " make turn");
            pressedBtn.setText(secondPlayer.znak);
        }
        pressedBtn.setEnabled(false);
        if (++actions > 8)
            System.out.println("* gg wp go next! *");
        isFirstPlayer = !isFirstPlayer;
    }
}
 
class Player {
    String znak;
    String name;
 
    public Player(String name, String znak) {
        this.name = name;
        this.znak = znak;
    }
}