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当我运行以下代码时，我得到了 NullPointerException。此方法用于扫描目录并检索其中的所有文件（.java），然后计算 NLOC 和 NLC。

所以这里是代码：

public void listFilesForFolder(final File folder) throws IOException {
    List<String> lines;
    for (File fileEntry : folder.listFiles()) {  // <<--- exception here
      if (fileEntry.isDirectory()) {
        listFilesForFolder(fileEntry);
      } else {
        if (fileEntry.isFile()) {
          temp = fileEntry.getName();
          if ((temp.substring(temp.lastIndexOf('.') + 1, temp.length()).toLowerCase()).equals("java")) {
            fileName = folder.getAbsolutePath() + "\\" + fileEntry.getName();
            try {
              lines = getLines(fileName);
              totalCommentCount += calcComments(lines);
              totalLOC += calcLOC(lines);

            } catch (IOException e) {
              System.out.println("File does not exist!" + e);
            }
          }
        }
      }
    }
    StringBuilder output = new StringBuilder();
    output.append("Comment Lines :").append(totalCommentCount);
    output.append("\n");
    output.append("Lines of Code (LOC) :").append(totalLOC);
    txtDisplayResults.setText(output.toString());
 }

这是错误消息（我使用 netbeans 作为 IDE）：

23-Jul-2013 13:17:53 scaj.GUI listFilesForFolder
SEVERE: null
java.lang.NullPointerException
    at scaj.GUI.listFilesForFolder(GUI.java:61)
    at scaj.GUI.listFilesForFolder(GUI.java:68)
    at scaj.GUI.bScanActionPerformed(GUI.java:326)
    at scaj.GUI.access$100(GUI.java:17)
    at scaj.GUI$2.actionPerformed(GUI.java:235)
    at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
    at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2318)
    at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
    at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
    at java.awt.Component.processMouseEvent(Component.java:6038)
    at javax.swing.JComponent.processMouseEvent(JComponent.java:3260)
    at java.awt.Component.processEvent(Component.java:5803)
    at java.awt.Container.processEvent(Container.java:2058)
    at java.awt.Component.dispatchEventImpl(Component.java:4410)
    at java.awt.Container.dispatchEventImpl(Container.java:2116)
    at java.awt.Component.dispatchEvent(Component.java:4240)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4322)
    at java.awt.LightweightDispatcher.processMouseEvent(Container.java:3986)
    at java.awt.LightweightDispatcher.dispatchEvent(Container.java:3916)
    at java.awt.Container.dispatchEventImpl(Container.java:2102)
    at java.awt.Window.dispatchEventImpl(Window.java:2429)
    at java.awt.Component.dispatchEvent(Component.java:4240)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:599)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)
4

2 回答 2

1

folder.listFiles()当文件夹不是目录（在本例中为目录）或发生 IO 错误时，返回 null。Web 服务器是否可能没有访问某些文件夹的正确权限？或者它们无法访问（它们通过网络连接）。

添加一个 nullcheckfolder.listFiles()并打印出它返回 null 的文件夹。这应该可以帮助您确定它发生的原因。如果找不到原因，请将发生问题的文件夹添加到问题中。

于 2013-07-23T12:51:30.467 回答
1

Your folder.listFiles() is returning null. The listFiles() method:

Returns null if this abstract pathname does not denote a directory, or if an I/O error occurs.

于 2013-07-23T12:59:30.560 回答