“零”和“交叉”项目中的java空指针异常

Question

我一直在一个项目上工作，该项目是创建一个零和十字架的游戏。我已经为这款游戏奠定了基础，目前正在进一步开发。但是，当我运行该程序时，选择AI进行第一步操作，返回以下代码行中的Java Null指针异常：

if(Game.Board[0][0].getText().equals(Game.Board[1][1].getText()) && Game.Board[0][0].getText().equals(Game.PlayerMark))

Game.Boarda由3x3的Jbutton组成。PlayerMark是一个可以包含"X“或"O”的字符串。

如何解决这个问题？

调用AI方法的位置：

    public void StartGame()
    {
         SideAssigner();
         State = true;

         if ( AIGame == true && FirstTurn ==true)
         {
             Computer.AI();

         }

         while ( State = true )
         {

             WinValidator();

         }

    }

控制台框中的消息：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at Computer.AI(Computer.java:19)
    at Game.StartGame(Game.java:179)
    at Game$10.actionPerformed(Game.java:739)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$400(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Sour

更新:下面是如何确定每个JBUtton属性的示例：

        Button1.setText("");
        Button1.setEnabled(false);
        Button1.addActionListener(new ActionListener()
        {
            public void actionPerformed(ActionEvent e)
            {
                if ( State == true && playerO == true && PlayerGame == true )
                {
                    isEmpty = false;
                    Button1.setText("O");
                    // WinValidator
                    // TurnChecker ??
                }

                else if ( State == true && playerX == true && PlayerGame == true )
                {
                    isEmpty = false;
                    Button1.setText("X");
                    // WinValidator
                    // TurnChecker
                }

                else if ( State == true && computerO == true && AIGame == true)
                {
                    isEmpty = false;
                    // Call Computer Class
                    // WinValidator
                    // TurnChecker
                }

                else if ( State == true && computerX == true && AIGame == true)
                {
                    isEmpty = false;
                    // Call Computer Class
                    // WinValidator
                    // TurnChecker
                }

            }

        });

AI方法(它的片段，否则会显示太多)：

public static void AI() {

     for(int i=0; i<3; i++ )
     {


         for (int j=0; j<3; j++)
         {

             // Diagonal Defensive Strategy 

             if(Game.Board[0][0].getText().equals(Game.Board[1][1].getText()) && Game.Board[0][0].getText().equals(Game.PlayerMark))
             {

                    if( !Game.Board[2][2].getText().equals(Game.ComputerMark) && !Game.Board[2][2].getText().equals(Game.PlayerMark))
                    {
                        Game.Board[2][2].setText(Game.ComputerMark);
                        MadeMove = true;
                        return;
                    }
                }

                if(Game.Board[2][2].getText().equals(Game.Board[1][1].getText()) && Game.Board[2][2].equals(Game.PlayerMark))
                {

                    if( Game.Board[0][0].getText().equals(Game.ComputerMark) && !Game.Board[0][0].getText().equals(Game.PlayerMark))
                    {
                        Game.Board[0][0].setText(Game.ComputerMark);
                        MadeMove = true;
                        return;
                    }
                }

                if(Game.Board[0][0].getText().equals(Game.Board[1][1].getText()) && Game.Board[0][0].getText().equals(Game.PlayerMark))
                {
                    if( !Game.Board[2][2].getText().equals(Game.ComputerMark) && !Game.Board[2][2].getText().equals(Game.PlayerMark))
                    {
                        Game.Board[2][2].setText(Game.ComputerMark);
                        MadeMove = true;
                        return;
                    }
                }

Answer 1

下面是如何解决NullPointerException的问题。你应该学会如何自己解决这些问题，因为你会遇到很多这样的问题：

查看堆栈跟踪：

at Computer.AI(Computer.java:19)
at Game.StartGame(Game.java:179)

找到跟踪顶部的行：

if(Game.Board[0][0].getText().equals(Game.Board[1][1].getText()) && Game.Board[0][0].getText().equals(Game.PlayerMark))

如果看不到错误，请将该行拆分为更小的语句：

tmp = Game.Board[0];
tmp2 = tmp1[0];
tmp3 = Game.Board[1];
tmp4 = tmp3[1];

等-我不确定是什么类型，但你会知道的。

再运行一次，看看它掉在哪里了。行号现在将准确地告诉您哪条语句失败了。该语句中的引用必须为空。

如果您不知道引用为空的原因，请按照逻辑返回并重复上面的更改。

您还可以学习在诸如Eclipse之类的IDE中使用调试器。