File.renameTo() fails but works after creating FileOutputStream object it worked, Why?

Question

[EDIT] I was not able to rename my file with renameTo() method of File class. Okay I searched and found a question explaining the same

File.renameTo() fails?

Also I read the Java Doc for renameTo() which says:

Many aspects of the behavior of this method are inherently platform-dependent: The rename operation might not be able to move a file from one filesystem to another, it might not be atomic, and it might not succeed if a file with the destination abstract pathname already exists. The return value should always be checked to make sure that the rename operation was successful.

Okay, I understand that renameTo() method is platform-dependent.

Then I created the object of FileOutputStream and called close() method, now I tried renameTo() method and my file got renamed,

Question:

• I was not able to understand the reason why after creating the object of FileOutputStream my renameTo() method worked?

Environment: Windows XP, User: Administrator

Code:

    File f = null;
    File f1 = null;
    boolean isFileRenamed = false;

    try {
        // create new File objects
        f = new File("C:\\originalFile.txt");
        f1 = new File("C:\\renamedFile.txt");

        // I need to write following code to rename the file
        // I tried without FileOutputStram object but then renameTo() did not work
        FileOutputStream fos = new FileOutputStream(f);
        fos.close();

        isFileRenamed = f.renameTo(f1);
        System.out.print("File renamed? " + isFileRenamed);

    } catch (Exception e) {
        e.printStackTrace();
    }

Searching for answer why renameTo() method worked after creating object of FileOutputStram. Also my application use Java1.6 so my option for Files class is closed. I will have to use renameTo() method only

Answer 1

It's not a bug in the JDK. From the documentation:

Many aspects of the behavior of this method are inherently platform-dependent: The rename operation might not be able to move a file from one filesystem to another, it might not be atomic, and it might not succeed if a file with the destination abstract pathname already exists. The return value should always be checked to make sure that the rename operation was successful.

(My emphasis)

Different drives are different filesystems. Moving a file between file systems requires copying the file's data from the old filesystem to the new, and when the copy is complete, then deleting the file in its original location. renameTo doesn't take on that work, it's for the simple case where the file can simply be moved within the filesystem.

---

You say below that it doesn't even work within a file system. Note that if you're using Windows 7, you have to be running as Administrator to create files in the root of the C: drive.

This works if I run in a command prompt as Administrator:

Example code:

import java.io.*;

public class FileMove
{
    public static final void main(String[] args) {
        File f = null;
        File f1 = null;
        boolean bool = false;

        try {
            // create new File objects
            f = new File("C:\\test.txt");
            f1 = new File("C:\\renamed.txt");

            bool = f.renameTo(f1);

            System.out.print("File renamed? " + bool);

        } catch (Exception e) {
            // if any error occurs
            e.printStackTrace();
        }
    }
}

Example run:

C:\>echo "Testing 1 2 3">test.txt
C:\>type c:\test.txt
"Testing 1 2 3"
C:\>type c:\renamed.txt
The system cannot find the file specified.
C:\>java -cp . FileMove
File renamed? true
C:\>type renamed.txt
"Testing 1 2 3"
C:\>

But as millimoose points out in the comments, there's the Files.Move method.