why is my code not showing up the x$\text{'}$s and o$\text{'}$s in my display? here is my code.

package games.boards;

import java.awt.event.ActionEvent;

import javax.swing.$*$;

import javax.swing.JFrame;

import javax.swing.SwingUtilities;

import games.utilities.FileManager;

import java.awt.event.ActionEvent;

@SuppressWarnings$(\{$ "serial", "unused" $\})$

public class BoardGameTester extends JFrame $\{$

private Board gb;

private int turn;

public static void main$($String$[]$ args$)\{$

SwingUtilities.invokeLater$($new Runnable$()$

$\{$

public void run$()\{$new BoardGameTester$()$;

$\}$

$\})$;$\}$

private void takeTurn$($Cell c$)\{$

Mark curMark $=($turn$++\%2==0)?$

Mark.NOUGHT: Mark.CROSS;

gb$.$setCell$($curMark$,$c$.$getRow$(),$c$.$getColumn$())$;

$\}$

private BoardGameTester$()\{$

gb $=$ new Board$(3,3,$ new ActionListener$()\{$

public void actionPerformed$($ActionEvent ae$)\{$

Cell c $=($Cell$)$ ae$.$getSource$()$;

takeTurn$($c$)$;

$\}$

$\})$;

this.add$($gb$)$;

this.setDefaultCloseOperation$($EXIT$\_$ON$\_$CLOSE$)$;

this.setTitle$("$TIC$-$TAC$-$TOE"$)$;

this.setSize$(300,300)$;

this.setVisible$($true$)$;

$\}$

$\}$

package games.boards;

import javax.swing.JButton;

import java.awt.Graphics;

import java.awt.Graphics$2$D;

import java.awt.BasicStroke;

import java.awt.Color;

import java.util.Scanner;

import java.awt.$*$;

class Cell extends JButton $\{$

private Mark content;

private int row, column;

public Cell$($int row, int column$)\{$

this.row $=$ row;

this.column $=$ column;

content $=$ Mark.EMPTY;

$\}$

public Mark getContent$()\{$

return content;

$\}$

public void setContent$($Mark content$)\{$

this.content $=$ content;

$\}$

public int getRow$()\{$

return row;

$\}$

public int getColumn$()\{$

return column;

$\}$

@Override

public void paintComponent$($Graphics g$)\{$

super.paintComponent$($g$)$;

int offset $=5$;

Graphics$2$D g$2=($Graphics$2$D$)$ g;

g$2.$setStroke$($new BasicStroke$(5))$;

switch $($content$)\{$

case NOUGHT:

g$.$setColor$($Color$.$RED$)$;

g$.$drawOval$($offset$,$offset,

this.getWidth$()-$offset,

this.getHeight$()-$offset$)$;

break;

case CROSS:

g$2.$setColor$($Color$.$BLACK$)$;

g$2.$drawLine$($

offset, offset,

this.getWidth$()-$ offset $,$

this.getHeight$()-$ offset $)$;

g$2.$drawLine$($

this.getWidth$()-$ offset,

offset, offset,

this.getHeight$()-$ offset$)$;

break;

$\}$

$\}$

public void addActionListener$($ActionListener ah$)\{$

$\}$

$\}$

package games.boards;

import javax.swing.$*$;

import java.awt.GridLayout;

@SuppressWarnings$("$serial$")$

public class Board extends JPanel $\{$

private Cell$[][]$ cells;

public Board$($int rows, int columns, ActionListener ah$)\{$

cells $=$ new Cell$[$rows$][$columns$]$;

this.setLayout$($new GridLayout$(3,3))$;

for$($ int r $=0$; r $<$ cells.length; r$++)\{$

for $($int c $=0$; c $<$ cells$[$r$].$length; c$++)\{$

cells$[$r$][$c$]=$ new Cell$($r$,$c$)$;

this.add$($cells$[$r$][$c$])$;

cells$[$r$][$c$].$addActionListener$($ah$)$;

$\}$

$\}$

$\}$

public void setCell$($Mark mark, int row, int column$)$ throws IllegalArgumentException $\{$

try $\{$

if $($cells$[$row$][$column$].$getContent$()==$ Mark.EMPTY$)\{$

cells$[$row$][$column$].$setContent$($mark$)$;

$\}$ else $\{$

throw new IllegalArgumentException$("$play already occupied"$)$;

$\}$

$\}$ catch $($IllegalArgumentException e$)\{$

System.out.println$("$invalid cell selection"$)$;

$\}$

$\}$

@Override

public String toString$()\{$

StringBuilder str $=$ new StringBuilder$()$;

for$($ int r $=0$; r $<3$; r$++)\{$

str$.$append$("|")$;

for $($int c $=0$; c $<3$; c$++)\{$

switch$($cells$[$r$][$c$].$getContent$())$

$\{$

case NOUGHT:

str$.$append$("0")$;

break;

case CROSS:

str$.$append$("$X$")$;

break;

case YELLOW:

str$.$append$("$Y$")$;

break;

case RED:

str$.$append$("$R$")$;

break;

case BLUE:

str$.$append$("$B$")$;

break;

case GREEN:

str$.$append$("$G$")$;

break;

case MAGENTA:

str$.$append$("$M$")$;

break;

case ORANGE:

str$.$append$("$O$")$;

break;

default: $//$Empty

str$.$append$("")$ ;

$\}$

str$.$append$("|")$;

$\}$

str$.$append$("")$;

$\}$

return str$.$toString$()$;

$\}$

$\}$

package games.boards;

public class GridLayout $\{$

public GridLayout$()\{$

$//$ TODO Auto$-$generated constructor stub

$\}$

public static void main$($String$[]$ args$)\{$

$//$ TODO Auto$-$generated method stub

$\}$

$\}$