继我之前关于这个集中游戏的问题之后，我一直在努力尝试运行它的特定部分时遇到了java.lang.NullPointerException而我无法找出导致它的原因，它只是出现了在netbeans中指向我的主要方法。
Exception in thread "main" java.lang.NullPointerException
at concentrate.Concentrate.main(Concentrate.java:281)
这是错误出现的代码或页面，起初我认为它可能与我正在运行的playGame方法有关，但似乎没有任何改变。即使我从内部移除了所有东西，所以我再次来堆栈溢出寻求帮助。
package concentrate;
import static concentrate.HighscoreManager.scores;
import static concentrate.Score.nameField;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.*;
import java.util.logging.Logger;
import javax.swing.*;
public final class Concentrate extends JFrame implements ActionListener {
//below are all the variables declared for the gui and the game program itself
private final JFrame window = new JFrame("Concentrate");
private final int WINDOW_WIDTH = 330;
private final int WINDOW_HEIGHT = 485;
private JButton exitBtn, scoresBtn, resetButton;
public static ArrayList<Card> gameBtn;
public static int Point = 46;
public static int numCards = 16;
public static JLabel Score;
public static GameButtonPanel gamePnl;
private final Panel buttonPnl = new Panel();
private final Panel scorePnl = new Panel();
private GameButtonListener buttonListener; // Listener for the button actions
private GameButtonPanel gui; // The GUI this game controls
Concentrate game;
Random rand = new Random();
private int cardVal;
private GameButtonPanel theGUI;
//update score checks and sets the score on the main board
public static void updateScore() {
Score.setText("Score: " + Point);
}
public Concentrate(){
//below is calling the create gui function and set variables for it width and close operation
createGUI();
createpanels();
window.setTitle("Concentrate");
window.setDefaultCloseOperation(EXIT_ON_CLOSE);
window.setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
window.setVisible(true);
shuffleButtons();
gui = theGUI;
gamePnl = new GameButtonPanel();
game = gamePnl.game;
buttonListener = new GameButtonListener();
// Adds each button to the actions listener
for(Card c : gameBtn)
c.addActionListener(buttonListener);
}
//createpanels sets diffrent panels within windows to add the buttons and score on organised from top, main and bottom
public void createpanels()
{
/*gameBtn = new ArrayList<>(numCards * 2);*/
gameBtn = new ArrayList<>(numCards);
gamePnl = new GameButtonPanel(shuffleButtons());
//below adds the cards to the panel based on the number of them
for(int i = 0; i < numCards; i++)
{
Card cb = new Card(i);
gameBtn.add(cb);
}
buttonPnl.add(scoresBtn);
buttonPnl.add(exitBtn);
buttonPnl.add(resetButton);
gamePnl.setLayout(new GridLayout(4, 4));
buttonPnl.setLayout(new GridLayout(1, 0));
scorePnl.add(Score);
scorePnl.setLayout(new GridLayout(1, 0));
window.add(scorePnl, BorderLayout.NORTH);
window.add(gamePnl, BorderLayout.CENTER);
window.add(buttonPnl, BorderLayout.SOUTH);
}
public void createGUI() {
buttonListener = new GameButtonListener();
Score = new JLabel("Score: " + Point);
exitBtn = new JButton("Exit");
exitBtn.addActionListener(this);
scoresBtn = new JButton("Leaderboard");
scoresBtn.addActionListener(this);
resetButton = new JButton("Reset");
resetButton.addActionListener(this);
}
public static ArrayList<Card> shuffleButtons() {
Collections.shuffle(Arrays.asList(gameBtn));
layoutButtons();
return gameBtn;
}
public static void layoutButtons() {
for (JButton button : gameBtn) {
gamePnl.add(button);
}
}
//the code below is for the lower menu buttons
@Override
public void actionPerformed(ActionEvent e)
{
//this is the exit button displayed onthe bottomof the gui
if (exitBtn == e.getSource())
{
System.exit(0);
}
//this is the button at the botto of the gui which calls on the leaderboard frame
if (scoresBtn == e.getSource())
{
new Leaderboard().setVisible(true);
}
if (resetButton == e.getSource())
{
shuffleButtons();
}
}
public void reset()
{
// Unhide all the card buttons and set them face down
for(Card cb : gameBtn)
{
cb.setFaceDown();
cb.setVisible(true);
}
}
public void playGame(){
int PairsFound;
int stillPlaying;
JButton buttonPressed;
Card button1, button2;
stillPlaying = JOptionPane.YES_OPTION;
while(stillPlaying == JOptionPane.YES_OPTION)
{
PairsFound = 0;
buttonPressed = null;
// Loop until all the cards are matched.
while(PairsFound != cardVal / 2){
// Wait for first card to be pressed
buttonPressed = buttonListener.waitForButton();
if(buttonPressed instanceof Card)
{
button1 = (Card)buttonPressed;
button1.setFaceUp();
}
else
{
if(buttonPressed.getActionCommand().equals(gameBtn))
System.out.println("button was"+ gameBtn +"pressed");
break;
}
// Wait for second card to be pressed
buttonPressed = buttonListener.waitForButton();
if(buttonPressed instanceof Card)
{
button2 = (Card)buttonPressed;
button2.setFaceUp();
}
else
{
if(buttonPressed.getActionCommand().equals(exitBtn))
stillPlaying = JOptionPane.NO_OPTION;
break;
}
// Unflip the cards if they are not equals or if they are the
// same card (if they refer to the same object)
if(!button1.equals(button2) || button1 == button2){
((Card)button1).setFaceDown();
((Card)button2).setFaceDown();
Point = Point - 1;
}
else
{
button1.setVisible(false); // Hide the pair once found.
button2.setVisible(false);
PairsFound++;
}
// If found all matching pairs.
if(PairsFound == cardVal / 2)
{
}
}
}
}
private static final Logger LOG = Logger.getLogger(Concentrate.class.getName());
public static void main(String[] args)
{
Concentrate concentrate = new Concentrate();
concentrate.game.playGame();
}
}
对不起，如果我的代码是一个混乱仍然相当新的java，仍然学习任何帮助将不胜感激谢谢。
我不会说这是一个重复的问题，因为我没有问什么是空指针具体我问是什么导致它被抛入我的java程序但是也许我错了我不记得问到底是什么这是一个NullPointerException。
答案 0 :(得分：1)
显然空指针异常来自这一行：
concentrate.game.playGame();
你知道专注不是空的，因为你刚刚成功构建它;如果它没有被成功构造，则会从集中构造函数抛出异常并且不会到达此行。这意味着game为空。
现在我们回到Concentrate构造函数并查看game初始化的位置。它似乎在以下行中初始化：
game = gamePnl.game;
您没有显示gamePnl的构造函数，但结论是GamePanel构造函数无法初始化它自己的game成员，因此该成员为null并且concent.game也最终成为空。
您可能需要重构代码以创建集中游戏或游戏面板，然后将其传递给另一个的构造函数。事实上，他们似乎都指向另一方，这是一个难以正确设置的情况。
答案 1 :(得分：0)
我不知道这是不是问题 但你有一条线： gui = theGUI;
我在代码中找不到安装变量theGUI的地方。