当我运行以下代码时,我得到一个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());
}
以下是错误消息(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)
答案 0 :(得分:1)
folder.listFiles()
返回null,当文件夹不是目录(在这种情况下是这样)或发生IO错误时。 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)。
向folder.listFiles()
添加一个nullcheck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,请在问题中添加正在发生的文件夹。
答案 1 :(得分:1)
您的folder.listFiles()返回null。 listFiles()方法:
Returns null if this abstract pathname does not denote a directory, or if an I/O error occurs.