listFiles() returns null when it shouldn't. It used to work properly until recently and hasn't been modified

Question

public static void main(String[] args) throws InterruptedException {
    // TODO Auto-generated method stub
    while(true)
    {
        ArrayList<File> wallpapers = new ArrayList<File>();
        File dir = new File("C:/Windows/System32/oobe/info/backgrounds/");
        if(dir.listFiles() == null)
            System.out.println("Empty");
        for(File img : dir.listFiles())
        {
            if(img.getName().endsWith(".jpg") && img.getName() != "backgroundDefault.jpg")
                wallpapers.add(img);
        }
        File current = new File("C:/Windows/System32/oobe/info/backgrounds/backgroundDefault.jpg");
        int i = 1;
        for(File img : wallpapers)
        {
            File f = new File("C:/Windows/System32/oobe/info/backgrounds/"+ i++ +".jpg");
            current.renameTo(f);
            File file = new File("C:/Windows/System32/oobe/info/backgrounds/backgroundDefault.jpg");
            img.renameTo(file);
            Thread.sleep(60000);
        }

    }
}   }
}

This code changes the background image of the Windows Log In screen every minute. listFiles() returns null for dir and I get a NullPointerException on for(File img : dir.listFiles()). I thought there may be a problem with file rights so I tried to change the file path to a directory I have on my Desktop and it works fine. So I'm assuming I can't access system files because my program doesn't have enough rights. Let me also precise that this code used to work fine until recently. It hasn't been modified. I just found out that my Log In Wallpaper doesn't change anymore. Even when the program did work I couldn't modify the file name when I launched the program through Eclipse but I would export it as .jar and schedule it with Task Scheduler with highest privileges to give it admin rights and it worked without any problems until recently. I also tried ignoring the errors thinking they were related to access rights and tried to launch my executable jar with highest privileges through Task Scheduler and also using a batch file. I even tried launching the jar through a cmd I opened with Administrator Rights to no avail it still says NullPointerException in the cmd. I'm kind of lost and would appreciate any help.

Answer 1

On Windows 7 (and later) the process will have to run with elevated privileges to write to C:/Windows and similar directories. But if that was the problem it would result in a different error message.

What I suspect: When running a 32-bit JVM under 64-bit Windows new File("C:/Windows/System32") will point to C:\Windows\SysWOW64 and there is no info-Folder under C:\Windows\SysWOW64\oobe

As a test:

public static void main(String[] args) {
    File sysdir = new File("C:/Windows/System32/oobe/info");
    for(File file:sysdir.listFiles()) {
        System.out.println(file.getName());
    }
}

runs fine with 64-bit-JRE and throws NullPointerException under 32-bit-JRE on Windows 7 64-bit.

So perhaps you or another application recently installed a 32-bit-jre or changed your path to point to a 32-bit-jre and thus broke your application.