tic tac toe 返回 java.lang.NullPointerException

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英文:

tic tac toe returns java.lang.NullPointerException

问题

代码部分不提供翻译，以下是代码中的注释：

// ...
package tictactoeb;

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

// ...

public class TicTacToe implements ActionListener
{
    String check[] = new String[9];
    JButton buttons[] = new JButton[9];
    int num = 0;
    ImageIcon X = new ImageIcon("X.png");
    ImageIcon O = new ImageIcon("O.png");
    JPanel layout = new JPanel();
    JFrame window = new JFrame("TicTacToe");
    String letter = " ";
    ImageIcon img;
    String winner;

    public static void main(String[] args) 
    {
        new TicTacToe();
    }

    public TicTacToe() 
    {
        for (String s : check)
            s = " ";
        JFrame window = new JFrame("TicTacToe");
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setBounds(400, 400, 400, 400);
        window.setLayout(new GridLayout(3, 3));
        for (int i = 0; i <= 8; i++) {
            buttons[i] = new JButton(" ");
            this.buttons[i] = buttons[i];
            buttons[i].setIcon(null);
            buttons[i].addActionListener(this);
            window.add(buttons[i]);
        }
        window.setVisible(true);
    }

    @Override
    public void actionPerformed(ActionEvent e) 
    {
        JButton buttonClicked = (JButton) e.getSource();
        if (num % 2 == 0) {
            letter = "X";
            img = X;
        } else {
            letter = "O";
            img = O;
        }
        for (int i = 0; i < 9; ++i)
            if (buttonClicked.equals(buttons[i])) {
                buttons[i].setIcon(img);
                check[i] = letter;
            }
        if (checkWinner(letter)) {
            System.out.println("Winner");
            clearBoard();
        }
        num++;
    }

    // ...
}

// ...
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at tictactoeb.TicTacToe.checkAdjacent(TicTacToe.java:109)
    at tictactoeb.TicTacToe.checkWinner(TicTacToe.java:85)
    at tictactoeb.TicTacToe.actionPerformed(TicTacToe.java:73)
    // ...
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at tictactoeb.TicTacToe.checkAdjacent(TicTacToe.java:109)
    at tictactoeb.TicTacToe.checkWinner(TicTacToe.java:85)
    at tictactoeb.TicTacToe.actionPerformed(TicTacToe.java:73)
    // ...

请注意，我只翻译了注释以外的文本内容。

英文:

Its throwing the exception on the if statement within the checkAdjacent method, but it traces back to the checkWinner method. none of the objects in checkAdjacent are set to null, so something else must be. maybe one of the JButtons objects? Is is as simple as a null object? should i just be trying to handle the exception instead?

package tictactoeb;

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;


public class TicTacToe implements ActionListener
{
	String check[] =  new String[9];
	JButton buttons[] = new JButton[9];
	int num = 0;
	ImageIcon X = new ImageIcon(&quot;X.png&quot;);
	ImageIcon O = new ImageIcon(&quot;O.png&quot;);
	JPanel layout = new JPanel();
	JFrame window = new JFrame(&quot;TicTacToe&quot;);
	String letter = &quot; &quot;;
	ImageIcon img;
	String winner;
	public static void main(String[] args) 
	{
		new TicTacToe();
	}
	
	public TicTacToe() 
	{
		for(String s : check)
			s = &quot; &quot;;
		JFrame window = new JFrame(&quot;TicTacToe&quot;);
		window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		window.setBounds(400,400,400,400);
		window.setLayout(new GridLayout(3,3));
		for(int i = 0; i &lt;= 8; i++)
        {
            buttons[i] = new JButton(&quot; &quot;);
            this.buttons[i] = buttons[i];
            buttons[i].setIcon(null);
            buttons[i].addActionListener(this);
            
            window.add(buttons[i]);  
        }
		window.setVisible(true);
	}
	

		@Override
	public void actionPerformed(ActionEvent e) 
	{
		JButton buttonClicked = (JButton)e.getSource(); 
		if(num%2 == 0)
		{	
			letter = &quot;X&quot;;
			img = X;
		}
		else
		{
			letter = &quot;O&quot;;
			img = O;
		}   
		for(int i = 0;i&lt;9; ++i)
			if(buttonClicked.equals(buttons[i]))
			{
				buttons[i].setIcon(img);
				check[i] = letter;
				
			}
        if(checkWinner(letter))
        {
        	System.out.println(&quot;Winner&quot;);
        	clearBoard();
        }
        num++;
			
	}
	
	public boolean checkWinner(String ltr) 
	{
		boolean ref = false;
		if(checkAdjacent(0,1,ltr) &amp;&amp; checkAdjacent(1,2,ltr))
			ref = true;
		else if(checkAdjacent(3,4,ltr) &amp;&amp; checkAdjacent(4,5,ltr))
			ref = true;
		else if(checkAdjacent(6,7,ltr) &amp;&amp; checkAdjacent(7,8,ltr))
			ref = true;
			
		else if(checkAdjacent(0,3,ltr) &amp;&amp; checkAdjacent(3,6,ltr))
			ref = true;
		else if(checkAdjacent(1,4,ltr) &amp;&amp; checkAdjacent(4,7,ltr))
			ref = true;
		else if(checkAdjacent(2,5,ltr) &amp;&amp; checkAdjacent(5,8,ltr))
			ref = true;
			
		else if(checkAdjacent(0,4,ltr) &amp;&amp; checkAdjacent(4,8,ltr))
			ref = true;
		else if(checkAdjacent(2,4,ltr) &amp;&amp; checkAdjacent(4,6,ltr))
			ref = true;
		return ref;
	}
		
	public boolean checkAdjacent(int pos1,int pos2, String ltr) 
	{
		boolean ref = false;
		if(check[pos1].equals(ltr) &amp;&amp; check[pos2].equals(ltr))
			ref = true;
		else
			ref = false;
		return ref;
	}
	
	public void clearBoard() 
	{
		for(JButton i : buttons)
		{
			i.setIcon(null);
		}
		for(String c : check)
			c = &quot; &quot;;
	}
	
		
}

Exception in thread &quot;AWT-EventQueue-0&quot; java.lang.NullPointerException
	at tictactoeb.TicTacToe.checkAdjacent(TicTacToe.java:109)
	at tictactoeb.TicTacToe.checkWinner(TicTacToe.java:85)
	at tictactoeb.TicTacToe.actionPerformed(TicTacToe.java:73)
	at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1967)
	at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2308)
	at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405)
	at java.desktop/javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:262)
	at java.desktop/javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:279)
	at java.desktop/java.awt.Component.processMouseEvent(Component.java:6636)
	at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3342)
	at java.desktop/java.awt.Component.processEvent(Component.java:6401)
	at java.desktop/java.awt.Container.processEvent(Container.java:2263)
	at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:5012)
	at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2321)
	at java.desktop/java.awt.Component.dispatchEvent(Component.java:4844)
	at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4918)
	at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Container.java:4547)
	at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Container.java:4488)
	at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2307)
	at java.desktop/java.awt.Window.dispatchEventImpl(Window.java:2762)
	at java.desktop/java.awt.Component.dispatchEvent(Component.java:4844)
	at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:772)
	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:95)
	at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:745)
	at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:743)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
	at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:742)
	at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
	at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
Exception in thread &quot;AWT-EventQueue-0&quot; java.lang.NullPointerException
	at tictactoeb.TicTacToe.checkAdjacent(TicTacToe.java:109)
	at tictactoeb.TicTacToe.checkWinner(TicTacToe.java:85)
	at tictactoeb.TicTacToe.actionPerformed(TicTacToe.java:73)
	at java.desktop/javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1967)
	at java.desktop/javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2308)
	at java.desktop/javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:405)
	at java.desktop/javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:262)
	at java.desktop/javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:279)
	at java.desktop/java.awt.Component.processMouseEvent(Component.java:6636)
	at java.desktop/javax.swing.JComponent.processMouseEvent(JComponent.java:3342)
	at java.desktop/java.awt.Component.processEvent(Component.java:6401)
	at java.desktop/java.awt.Container.processEvent(Container.java:2263)
	at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:5012)
	at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2321)
	at java.desktop/java.awt.Component.dispatchEvent(Component.java:4844)
	at java.desktop/java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4918)
	at java.desktop/java.awt.LightweightDispatcher.processMouseEvent(Container.java:4547)
	at java.desktop/java.awt.LightweightDispatcher.dispatchEvent(Container.java:4488)
	at java.desktop/java.awt.Container.dispatchEventImpl(Container.java:2307)
	at java.desktop/java.awt.Window.dispatchEventImpl(Window.java:2762)
	at java.desktop/java.awt.Component.dispatchEvent(Component.java:4844)
	at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:772)
	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
	at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:95)
	at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:745)
	at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:743)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
	at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
	at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:742)
	at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
	at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
	at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
	at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

</details>

huangapple
  • 本文由 发表于 2020年4月8日 06:21:49
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