Why Is Java Saying these Files Are of Zero Length?

[Kevin Simonson]

I'm working on a computer with operating system Windows 10 Enterprise. On my D: drive in directory "Bug" I have two files, "Oops.Txt" and "Qf.Txt", of lengths 6 and 49 respectively. When I type in "D:", it takes me directly to that "\Bug" directory. (In other words, when I was last on my D: drive I was in that directory.) When I type "dir D:" I get a listing of those two files, and when I type in "dir D:\Bug" I get an identical listing of those two files.

C:\Users\Kevin\Java>dir D:
 Volume in drive D has no label.
 Volume Serial Number is 8CB3-F581

 Directory of D:\Bug

05/29/2024  08:13 AM    <DIR>          .
05/29/2024  08:13 AM    <DIR>          ..
05/29/2024  08:56 AM                 6 Oops.Txt
05/29/2024  08:15 AM                49 Qf.Txt
               2 File(s)             55 bytes
               2 Dir(s)  22,683,435,008 bytes free

C:\Users\Kevin\Java>dir D:\Bug
 Volume in drive D has no label.
 Volume Serial Number is 8CB3-F581

 Directory of D:\Bug

05/29/2024  08:13 AM    <DIR>          .
05/29/2024  08:13 AM    <DIR>          ..
05/29/2024  08:56 AM                 6 Oops.Txt
05/29/2024  08:15 AM                49 Qf.Txt
               2 File(s)             55 bytes
               2 Dir(s)  22,683,435,008 bytes free

C:\Users\Kevin\Java>

Now I've written file "MyDir.java" which consists of:

import java.io.File;
import java.io.PrintStream;

public class MyDir
{
  private static final PrintStream SY_O = System.out;

  public static void main ( String[] arguments)
  {
    if (arguments.length == 1)
    { String lctn = arguments[ 0];
      File drctry = new File( lctn);
      if (drctry.exists() && drctry.isDirectory())
      { for (File child : drctry.listFiles())
        { SY_O.println( child.getName() + ": " + child.length());
        }
      }
      else
      { SY_O
          .println
             ( "File \"" + lctn + "\" doesn't exist or isn't a directory!");
      }
    }
    else
    { SY_O.println( "Usage is");
      SY_O.println( "  java MyDir <lctn>");
    }
  }
}

When I run it I get:

C:\Users\Kevin\Java>j8 MyDir D:
Oops.Txt: 0
Qf.Txt: 0

C:\Users\Kevin\Java>j8 MyDir D:\Bug
Oops.Txt: 6
Qf.Txt: 49

C:\Users\Kevin\Java>

Why am I getting zero lengths for those two files when I execute "j8 MyDir D:"? It's getting the two files that are in my "Bug" directory. Why is it getting the two sizes wrong? Is there a way to fix my code so that I can execute "j8 MyDir D:" and get the correct results?

[Piet Souris]

When you type: D:,
then you get into the current directory in D, and that may not be D:\Bug. Perhaps that is the problem?

[Ron McLeod]

Other than renaming some variables, I ran your code as-is, and it seemed to work as your wanted:C:\tmp>D: D:\Bug>C: C:\tmp>dir D: Volume in drive D is Data Volume Serial Number is 1614-D792 Directory of D:\Bug 05/29/2024  09:32 AM    <DIR>          . 05/29/2024  09:32 AM    <DIR>          .. 05/29/2024  09:31 AM                 6 Ooops.Txt 05/29/2024  09:32 AM                49 Qf.Txt               2 File(s)             55 bytes               2 Dir(s)  540,079,120,384 bytes free C:\tmp>dir D:\Bug Volume in drive D is Data Volume Serial Number is 1614-D792 Directory of D:\Bug 05/29/2024  09:32 AM    <DIR>          . 05/29/2024  09:32 AM    <DIR>          .. 05/29/2024  09:31 AM                 6 Ooops.Txt 05/29/2024  09:32 AM                49 Qf.Txt               2 File(s)             55 bytes               2 Dir(s)  540,079,120,384 bytes free C:\tmp>java MyDir.java D: Ooops.Txt: 6 Qf.Txt: 49 C:\tmp>java MyDir.java D:\Bug Ooops.Txt: 6 Qf.Txt: 49

import java.io.File;

public class MyDir {
    public static void main(String[] arguments) {
        if (arguments.length == 1) {
            String location = arguments[0];
            File directory = new File(location);
            if (directory.exists() && directory.isDirectory()) {
                for (File child : directory.listFiles()) {
                    System.out.println(child.getName() + ": " + child.length());
                }
            } else {
                System.out.println("File \"" + location + "\" doesn't exist or isn't a directory!");
            }
        } else {
            System.out.println("Usage is");
            System.out.println("  java MyDir <lctn>");
        }
    }
}

Windows 10 and Java 17.0.7

[Mike Simmons]

Kevin, what is this "j8" command that you're running?

I'm guessing it may be an alias for a Java 8 runtime.  If so, can you try any other JDKs?  Something more modern?  This may be something that's been fixed in other versions.

[Tim Holloway]

It's dagngerous to assume what the current directory or even the current logged Windows drive is in Java. Other parts of the system might alter it without warning. Always use an
absolute path.

Mike, I believe "J8" is an IBM JVM. I've worked with J9, so the main puzzlement is whether that's a really old JVM or they just numbered arbitrarily.

[Rob Spoor]

The documentation of File.length() implies that 0L is returned whenever the length could not be determined. Try using Files.readAttributes(child.toPath(), BasicFileAttributes.class) and you'll probably see an exception instead.

[Kevin Simonson]

Ron McLeod wrote:Other than renaming some variables, I ran your code as-is, and it seemed to work as your wanted:C:\tmp>D: D:\Bug>C: C:\tmp>dir D: Volume in drive D is Data Volume Serial Number is 1614-D792 Directory of D:\Bug 05/29/2024  09:32 AM    <DIR>          . 05/29/2024  09:32 AM    <DIR>          .. 05/29/2024  09:31 AM                 6 Ooops.Txt 05/29/2024  09:32 AM                49 Qf.Txt               2 File(s)             55 bytes               2 Dir(s)  540,079,120,384 bytes free C:\tmp>dir D:\Bug Volume in drive D is Data Volume Serial Number is 1614-D792 Directory of D:\Bug 05/29/2024  09:32 AM    <DIR>          . 05/29/2024  09:32 AM    <DIR>          .. 05/29/2024  09:31 AM                 6 Ooops.Txt 05/29/2024  09:32 AM                49 Qf.Txt               2 File(s)             55 bytes               2 Dir(s)  540,079,120,384 bytes free C:\tmp>java MyDir.java D: Ooops.Txt: 6 Qf.Txt: 49 C:\tmp>java MyDir.java D:\Bug Ooops.Txt: 6 Qf.Txt: 49

import java.io.File;

public class MyDir {
    public static void main(String[] arguments) {
        if (arguments.length == 1) {
            String location = arguments[0];
            File directory = new File(location);
            if (directory.exists() && directory.isDirectory()) {
                for (File child : directory.listFiles()) {
                    System.out.println(child.getName() + ": " + child.length());
                }
            } else {
                System.out.println("File \"" + location + "\" doesn't exist or isn't a directory!");
            }
        } else {
            System.out.println("Usage is");
            System.out.println("  java MyDir <lctn>");
        }
    }
}

Windows 10 and Java 17.0.7

Ron, I just changed the name of your class from (MyDir) to (McLeod), giving me:

import java.io.File;
 
public class McLeod {
    public static void main(String[] arguments) {
        if (arguments.length == 1) {
            String location = arguments[0];
            File directory = new File(location);
            if (directory.exists() && directory.isDirectory()) {
                for (File child : directory.listFiles()) {
                    System.out.println(child.getName() + ": " + child.length());
                }
            } else {
                System.out.println("File \"" + location + "\" doesn't exist or isn't a directory!");
            }
        } else {
            System.out.println("Usage is");
            System.out.println("  java MyDir <lctn>");
        }
    }
}

But I get the same results:

C:\Users\Kevin\Java>j8 McLeod D:\Bug
Oops.Txt: 6
Qf.Txt: 49

C:\Users\Kevin\Java>j8 McLeod D:
Oops.Txt: 0
Qf.Txt: 0

C:\Users\Kevin\Java>

My command "j8" is just an alias for "\Langs\Java\8u40-windows-x64\bin\java".

[Carey Brown]

Java-8 dates back to 2014. Try something newer.

[Ron McLeod]

I don't have JDK 8u40 installed anywhere, but I tried using 8u202 on Windows 10 Pro v22H2 build 19045.2965 and I got the same (successful) results.

[Mike Simmons]

Aside from trying a more modern JDK, don't overlook Ron's previous comment about how the documentation for File.length() may explain this, and recommends using Files.readAttributes() to see if there's an error message.  You can go further and print out additional diagnostic info that may help:

  private static void examine(File file) {
    System.out.println("file: " + file);
    Path path = file.toPath();
    System.out.println("  absolutePath: " + path.toAbsolutePath());
    try {
      System.out.println("  realPath: " + path.toRealPath());
      BasicFileAttributes attrs = Files.readAttributes(path, BasicFileAttributes.class);
      System.out.println("  size: " + attrs.size());
      String type =
        attrs.isRegularFile() ? "REGULAR FILE"
        : attrs.isDirectory() ? "DIRECTORY"
        : attrs.isSymbolicLink() ? "SYMBOLIC LINK"
        : attrs.isOther() ? "OTHER"
        : "UNKNOWN";
      System.out.println("  type: " + type);
    } catch (IOException e) {
      e.printStackTrace();
    }
  }