Java贪吃蛇游戏高分更新功能崩溃问题求助

问题描述 #

用Java开发贪吃蛇游戏，需求是当applesEaten（本局得分）超过HighScore.txt中的现有高分时，更新该文件的记录。测试发现：

• 若本局得分未超过文件高分，游戏结束后正常显示得分与高分；
• 若本局得分超过现有高分，游戏崩溃，抛出java.util.NoSuchElementException异常。

报错堆栈信息 #

Exception in thread "AWT-EventQueue-0" java.util.NoSuchElementException
    at java.base/java.util.Scanner.throwFor(Scanner.java:937)
    at java.base/java.util.Scanner.next(Scanner.java:1594)
    at java.base/java.util.Scanner.nextInt(Scanner.java:2258)
    at java.base/java.util.Scanner.nextInt(Scanner.java:2212)
    at GamePanel.highScoreChecker(GamePanel.java:138)
    at GamePanel.gameOver(GamePanel.java:203)
    at GamePanel.draw(GamePanel.java:84)
    at GamePanel.paintComponent(GamePanel.java:50)
    at java.desktop/javax.swing.JComponent.paint(JComponent.java:1119)
    at java.desktop/javax.swing.JComponent.paintToOffscreen(JComponent.java:5311)
    at java.desktop/javax.swing.RepaintManager$PaintManager.paintDoubleBufferedImpl(RepaintManager.java:1657)
    at java.desktop/javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1632)
    at java.desktop/javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1570)
    at java.desktop/javax.swing.RepaintManager.paint(RepaintManager.java:1337)
    at java.desktop/javax.swing.JComponent._paintImmediately(JComponent.java:5259)
    at java.desktop/javax.swing.JComponent.paintImmediately(JComponent.java:5069)
    at java.desktop/javax.swing.RepaintManager$4.run(RepaintManager.java:879)
    at java.desktop/javax.swing.RepaintManager$4.run(RepaintManager.java:862)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
    at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.desktop/javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:862)
    at java.desktop/javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:835)
    at java.desktop/javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:784)
    at java.desktop/javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1898)
    at java.desktop/java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:318)
    at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:771)
    at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:722)
    at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:716)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
    at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
    at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:741)
    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)

核心问题代码 #

问题出在highScoreChecker()方法中，当更新高分后，复用了之前的fileByteStream来创建新的Scanner，而此时流已经读取完毕且未重置，导致读取失败：

public int highScoreChecker() {
    Scanner scnr = new Scanner(System.in); // 此处scnr未使用，可删除
    FileInputStream fileByteStream = null;
    Scanner inFS = null;
    
    try {
        fileByteStream = new FileInputStream("HighScore.txt");
        inFS = new Scanner(fileByteStream);
        prevHighScore = inFS.nextInt();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }
    
    if (applesEaten > prevHighScore) {
        try {
            FileWriter myWriter = new FileWriter("HighScore.txt");
            myWriter.write(applesEaten + "");
            myWriter.close();
            
            // 错误点：复用已读取过的fileByteStream，此时流已到末尾，无法读取新内容
            inFS = new Scanner(fileByteStream);
            highScore = inFS.nextInt();
        } catch (IOException e) {
            e.printStackTrace();
        }
    } else {
        highScore = prevHighScore;
    }
    
    return highScore;
}

解决方案 #

方案1：更新高分后直接使用当前applesEaten作为新高分 #

既然已经将applesEaten写入文件，新高分就是当前得分，直接赋值即可，无需重复读取文件：

public int highScoreChecker() {
    FileInputStream fileByteStream = null;
    Scanner inFS = null;
    prevHighScore = 0; // 默认初始高分0，防止文件不存在时变量未初始化
    
    try {
        fileByteStream = new FileInputStream("HighScore.txt");
        inFS = new Scanner(fileByteStream);
        if (inFS.hasNextInt()) { // 先判断是否有整数可读，避免文件为空时报错
            prevHighScore = inFS.nextInt();
        }
    } catch (FileNotFoundException e) {
        // 文件不存在时，默认高分0，后续会写入第一个得分
        System.out.println("HighScore.txt不存在，将创建新文件");
    } finally {
        // 关闭流，防止资源泄漏
        if (inFS != null) {
            inFS.close();
        }
        try {
            if (fileByteStream != null) {
                fileByteStream.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    
    if (applesEaten > prevHighScore) {
        try {
            FileWriter myWriter = new FileWriter("HighScore.txt");
            myWriter.write(String.valueOf(applesEaten));
            myWriter.close();
            highScore = applesEaten; // 直接使用当前得分作为新高分
        } catch (IOException e) {
            e.printStackTrace();
        }
    } else {
        highScore = prevHighScore;
    }
    
    return highScore;
}

方案2：重新打开输入流读取新高分 #

如果一定要从文件读取新高分，需要关闭旧流后重新创建新的FileInputStream：

public int highScoreChecker() {
    FileInputStream fileByteStream = null;
    Scanner inFS = null;
    prevHighScore = 0;
    
    try {
        fileByteStream = new FileInputStream("HighScore.txt");
        inFS = new Scanner(fileByteStream);
        if (inFS.hasNextInt()) {
            prevHighScore = inFS.nextInt();
        }
    } catch (FileNotFoundException e) {
        System.out.println("HighScore.txt不存在，将创建新文件");
    } finally {
        if (inFS != null) inFS.close();
        try { if (fileByteStream != null) fileByteStream.close(); } catch (IOException e) { e.printStackTrace(); }
    }
    
    if (applesEaten > prevHighScore) {
        try {
            FileWriter myWriter = new FileWriter("HighScore.txt");
            myWriter.write(String.valueOf(applesEaten));
            myWriter.close();
            
            // 重新打开文件读取新高分
            fileByteStream = new FileInputStream("HighScore.txt");
            inFS = new Scanner(fileByteStream);
            if (inFS.hasNextInt()) {
                highScore = inFS.nextInt();
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (inFS != null) inFS.close();
            try { if (fileByteStream != null) fileByteStream.close(); } catch (IOException e) { e.printStackTrace(); }
        }
    } else {
        highScore = prevHighScore;
    }
    
    return highScore;
}

额外优化点 #

• 删除未使用的Scanner scnr = new Scanner(System.in);，避免资源浪费；
• 增加流的关闭操作（使用finally块），防止资源泄漏；
• 添加inFS.hasNextInt()判断，避免文件为空时读取失败；
• 初始化prevHighScore为0，防止文件不存在时变量未初始化导致逻辑错误。

内容的提问来源于stack exchange，提问作者Evan Schulte