为什么java.io.File.listFiles（）抛出NPE而不是正确的异常？ [英] Why does java.io.File.listFiles() throw NPE instead of proper Exception?

问题描述

今天我写了一个小型Java程序来查找我的硬盘上的文件，部分原因是Windows缺少适当的文件，部分原因是因为它很有趣。它只是循环遍历目录的所有子节点，如果它们是目录，则递归地遍历所有子项。但是后来我有一个 NullPointerException 。经过一些 System.out.println（）的和一个 try-catch块我发现这发生在一些目录，如 D：\System卷信息， C：\Users\Public\Documents\My视频和 C：\ProgramData\Templates 。 Windows本身表示，当在Explorer地址栏中输入访问被拒绝时。当您探索时，他们似乎被锁定。 来源从 java.io.File 告诉我：

  public File [] listFiles（）{
 String [] ss = list（）; 
 if（ss == null）return null; //这行似乎是导致NPE 
 int n = ss.length; 
文件[] fs = new File [n]; （int i = 0; i  fs [i] = new File（ss [i]，this）; 
 
} 
 return fs; 
} 
  

我的问题是，为什么没有正确的说法， IOException ， SecurityException ，甚至一个 IDontCareWhatKindOfExceptionButPleaseNoNullPointerExceptionException ？

我知道我可以 try-catch 为 NPE ，或检查 null ，但我真的好奇为什么没有正确的异常抛出。

由于我不喜欢 try / catch 并检查 null 因为代码的美学价值，我做了一些令人讨厌的，令人讨厌的反思代码（很多虚伪的 try / catch 块），它模仿了一些方法从 java。 io.File ，因为它们是私有的，一些包（如 java.io.FileSystem ）不可见。因为我不在乎一些Windows文件，所以我只是忽略它们使用这个代码，给我一个空的数组：

  public static File [] listFiles（File mThis）{
 String [] ss = list（mThis）; 
 if（ss == null）{
 //System.out.println(\"ss为null）; 
 return new File [] {}; 
} 
 int n = ss.length; 
文件[] fs = new File [n]; （int i = 0; i  fs [i] = getNewFile（ss [i]，mThis）; 
 
} 
 return fs; 
} 
  

编辑：避免误解：我使用 try / catch ，我只是不喜欢他们美学。

EDIT2：我宁愿使用一个GUI比命令提示符。我非常不喜欢Windows Search GUI。

解决方案

简答：

• 安装JDK 7;


• 使用新的文件 API。






之后，您将永远不会再回到文件。




Today I wrote a small Java program to find files on my harddisk, partly because Windows lacks a proper one and partly because it was for fun. It simply iterates over all childs of a directory and recursively through all their children if they are directories. But then I had a NullPointerException. After some System.out.println()'s and a try-catch blockI found out this happened on some directories like D:\System Volume Information, C:\Users\Public\Documents\My Videos and C:\ProgramData\Templates. Windows itself says, when input in the Explorer address bar "Access denied". When exploring, they seem to be locked. The source from java.io.File tells me:

public File[] listFiles() {
    String[] ss = list();
    if (ss == null) return null; //This line seems to cause the NPE
    int n = ss.length;
    File[] fs = new File[n];
    for (int i = 0; i < n; i++) {
        fs[i] = new File(ss[i], this);
    }
    return fs;
}

My question is, why is there no proper say, IOException, SecurityException, or even an IDontCareWhatKindOfExceptionButPleaseNoNullPointerExceptionException?

I know I can just try-catch for NPEs, or check for null, but I'm really curious of why there's no proper Exception thrown.

Since I dislike try/catch and checking for null because of the aesthetic value of code, I made some nasty, nasty reflection code (with lots of hypocritical try/catch blocks) which emulates some methods from java.io.File, since they're private, and some packages (like java.io.FileSystem) are not visible. And because I do not care about some Windows files, I simply ignore them using this code, giving me an empty array:

public static File[] listFiles(File mThis) {
    String[] ss = list(mThis);
    if (ss == null) {
        //System.out.println("ss is null");
        return new File[] {};
    }
    int n = ss.length;
    File[] fs = new File[n];
    for (int i = 0; i < n; i++) {
        fs[i] = getNewFile(ss[i], mThis);
    }
    return fs;
}

EDIT: to avoid misinterpretations: I do use try/catch, I merely don't like them aesthetically.

EDIT2: I'd rather use a GUI than the command prompt. And I very much dislike the Windows Search GUI. It's almost painful to use.

解决方案

Short answer:

• install JDK 7;
• use the new Files API.

You will never come back to File after that.

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