Tic Tac Toe in Java with GUI.

The assignment is to write a code in Java for Tic Tac Toe gamewith GUI. I wrote a code where 2 palyers are playing, but wouldlike player vs computer. Please help to update current code so thatgame is player vs computer.

import java.awt.*;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import javax.swing.*;public class TicTacToe extends JPanel {    char playerSymbol = 'X';    JButton[] buttons = new JButton[9];    public TicTacToe() {        setLayout(new GridLayout(3,3));        setButtons();    }    public void setButtons()    {        for(int i = 0; i <= 8; i++)        {            buttons[i] = new JButton();            buttons[i].setText(" ");            buttons[i].setBackground(Color.white);            buttons[i].setOpaque(true);            buttons[i].setBorder(BorderFactory.createLineBorder(Color.GRAY, 3));            buttons[i].setFont(new Font(Font.SERIF, Font.BOLD, 100));            buttons[i].addActionListener(new ActionListener() {                @Override                public void actionPerformed(ActionEvent e) {                    JButton buttonClicked = (JButton) e.getSource();                    buttonClicked.setText(String.valueOf(playerSymbol));                    if(playerSymbol == 'X') {                        playerSymbol = 'O';                        buttonClicked.setBackground(Color.GRAY);                    }                    else {                        playerSymbol ='X';                        buttonClicked.setBackground(Color.PINK);                    }                    showWinner();                }            });            add(buttons[i]);        }    }    public void showWinner() {        if(checkWinner() == true) {            if(playerSymbol == 'X') playerSymbol = 'O';            else playerSymbol ='X';            JOptionPane pane = new JOptionPane();            int dialogResult = JOptionPane.showConfirmDialog(pane, "Game Over! "+ playerSymbol + " has won. Would you like to play again?","Game over!",                    JOptionPane.YES_NO_OPTION);            if(dialogResult == JOptionPane.YES_OPTION) resetGame();            else System.exit(0);        }        else if(checkDraw()) {            JOptionPane pane = new JOptionPane();            int dialogResult = JOptionPane.showConfirmDialog(pane, "It's a draw! Play again?","Game over!", JOptionPane.YES_NO_OPTION);            if(dialogResult == JOptionPane.YES_OPTION)  resetGame();            else System.exit(0);        }    }    private void resetGame() {        playerSymbol = 'X';        for(int i =0;i<9;i++) {            buttons[i].setText(" ");            buttons[i].setBackground(Color.white);        }    }    public boolean checkDraw() {        boolean full = true;        for(int i = 0 ; i<9;i++) {            if(buttons[i].getText().charAt(0) == ' ') {                full = false;            }        }        return full;    }    public boolean checkWinner() {        return (checkRows() == true || checkColumns() == true || checkDiagonals() == true);    }    public boolean checkRows() {        int i = 0;        for(int j = 0;j<3;j++) {            if( buttons[i].getText().equals(buttons[i+1].getText()) && buttons[i].getText().equals(buttons[i+2].getText())                    && buttons[i].getText().charAt(0) != ' ') {                return true;            }            i = i+3;        }        return false;    }    public boolean checkColumns() {        int i = 0;        for(int j = 0;j<3;j++) {            if( buttons[i].getText().equals(buttons[i+3].getText()) && buttons[i].getText().equals(buttons[i+6].getText())                    && buttons[i].getText().charAt(0) != ' ')            {                return true;            }            i++;        }        return false;    }    public boolean checkDiagonals() {        if(buttons[0].getText().equals(buttons[4].getText()) && buttons[0].getText().equals(buttons[8].getText())                && buttons[0].getText().charAt(0) !=' ')            return true;        else return (buttons[2].getText().equals(buttons[4].getText()) && buttons[2].getText().equals(buttons[6].getText())                && buttons[2].getText().charAt(0) !=' ');    }}

import javax.swing.*;public class Main {    public static void main(String[] args) {        JFrame board = new JFrame("TIC TAC TOE");        board.getContentPane().add(new TicTacToe());        board.setBounds(550,550,550,550);        board.setVisible(true);        board.setLocationRelativeTo(null);        board.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    }}