import java.awt.Color;
import java.awt.Graphics;
import java.awt.GridLayout;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.BorderLayout;

import javax.swing.CellEditor;
import javax.swing.JApplet;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.border.LineBorder;

public class TicTacToe extends JApplet {
    private char whoseTurn = 'X';
    private Cell[][] cells = new Cell[3][3];
    private JLabel jlblStatus = new JLabel("X's turn to play");
    public TicTacToe(){
        JPanel p = new JPanel(new GridLayout(3, 3,0,0));
        for(int i=0;i<3;i++)
            for(int j=0;j<3;j++)
                p.add(cells[i][j] = new Cell());
        p.setBorder(new LineBorder(Color.red, 1));
        jlblStatus.setBorder(new LineBorder(Color.yellow, 1));
        add(p,BorderLayout.CENTER);
        add(jlblStatus,BorderLayout.NORTH);
    }

    public boolean isFull(){
        for(int i=0;i<3;i++)
            for(int j=0;j<3;j++)
                if(cells[i][i].getToken()==' ')
                    return false;
        return true;
    }
    public boolean isWon(char token){
        for(int i=0;i<3;i++)
            if((cells[i][0].getToken()==token)
                    &&(cells[i][1].getToken()==token)
                    &&(cells[i][2].getToken()==token)){
                return true;
            }
        
        for(int j=0;j<3;j++)
            if((cells[0][j].getToken()==token)
                    &&(cells[1][j].getToken()==token)
                    &&(cells[2][j].getToken()==token)){
                return true;
            }
        
        if((cells[0][0].getToken()==token)
                &&(cells[1][1].getToken()==token)
                &&(cells[2][2].getToken()==token)){
            return true;
        }
        if((cells[0][2].getToken()==token)
                &&(cells[1][1].getToken()==token)
                &&(cells[2][0].getToken()==token)){
            return true;
        }
        return false;
    }
    public class Cell extends JPanel{
        private char token = ' ';
        public Cell(){
            setBorder(new LineBorder(Color.black, 1));
            addMouseListener(new MyMouseListener());
        }
        public char getToken(){
            return token;
        }
        public void setToken(char c){
            token = c;
            repaint();
        }
        protected void paintComponent(Graphics g){
            super.paintChildren(g);
            if(token == 'X'){
                g.drawLine(10, 10, getWidth()-10, getHeight()-10);
                g.drawLine(getWidth()-10, 10, 10, getHeight()-10);
            }
            else if(token == 'O'){
                g.drawOval(10, 10, getWidth()-20, getHeight()-20);
            }
        }
        private class MyMouseListener extends MouseAdapter{
            public void mouseClicked(MouseEvent e){
                if(token == ' '&&whoseTurn != ' '){
                    setToken(whoseTurn);
                    if(isWon(whoseTurn)){
                        jlblStatus.setText(whoseTurn+" Won! The game is over!");
                        whoseTurn = ' ';
                    }
                else if(isFull()){
                        jlblStatus.setText("Draw! The game is over!");
                        whoseTurn = ' ';
                    }
                else{
                        whoseTurn = (whoseTurn=='X')?'O':'X';
                        jlblStatus.setText(whoseTurn+"'s turn");
                    }
                }
            }
        }
    }
}

每个方块只会出现圈或叉为什么两个都出现了，把最大化一下又会恢复正常。。怎么一回事儿？

结贴率低，给分少，代码没注释。
别人怎么回答。。。

我错鸟嘛。。下次一定结贴，写注释。。。一定会做好的。。求解

显然是你没调用repaint方法，重绘组件，所以你最开始画出来的东西 虽然逻辑上消失了， 但是没有重画面板，所以在面板上没有消失，你可以增加一个线程来不停的重新绘制面板，或者定时调用repaint方法来重绘面板。

线程没学，怎么办呢？

用到了就学呗，还等什么。

好吧。。说的也对