You need to know all you can about a given file on disk.

Use a java.io.File object.

The File class has a number of “informational” methods. To use any of these, you must construct a File object containing the name of the file it is to operate upon. It should be noted up front that creating aFileobject has no effect on the permanent filesystem; it is only an object in Java’s memory. You must call methods on the File object in order to change the filesystem; as we’ll see, there are numerous “change” methods, such as one for creating a new (but empty) file, one for renaming a file, etc., as well as many informational methods. Table 10-1 lists some of the informational methods.

You can’t change the name stored in a File object; you simply create a new File object each time you need to refer to a different file.

import java.io.*;
import java.util.*;

/**
 * Report on a file's status in Java
 */
public class FileStatus {
    public static void main(String[] argv) throws IOException {

        // Ensure that a filename (or something) was given in argv[0]
        if (argv.length == 0) {
            System.err.println("Usage: Status filename");
            System.exit(1);
        }
        for (int i = 0; i< argv.length; i++) {
            status(argv[i]);
        }
    }

    public static void status(String fileName) throws IOException {
        System.out.println("---" + fileName + "---");

        // Construct a File object for the given file.
        File f = new File(fileName);

        // See if it actually exists
        if (!f.exists(  )) {
            System.out.println("file not found");
            System.out.println(  );    // Blank line
            return;
        }
        // Print full name
        System.out.println("Canonical name " + f.getCanonicalPath(  ));
        // Print parent directory if possible
        String p = f.getParent(  );
        if (p != null) {
            System.out.println("Parent directory: " + p);
        }
        // Check if the file is readable
        if (f.canRead(  )) {
            System.out.println("File is readable.");
        }
        // Check if the file is writable
        if (f.canWrite(  )) {
            System.out.println("File is writable.");
        }
        // Report on the modification time.
        Date d = new Date(  );
        d.setTime(f.lastModified(  ));
        System.out.println("Last modified " + d);

        // See if file, directory, or other. If file, print size.
        if (f.isFile(  )) {
            // Report on the file's size
            System.out.println("File size is " + f.length(  ) + " bytes.");
        } else if (f.isDirectory(  )) {
            System.out.println("It's a directory");
        } else {
            System.out.println("I dunno! Neither a file nor a directory!");
        }

        System.out.println(  );    // blank line between entries
    }
}

When run with the three arguments shown, it produces this output:

C:javasrcdir_file>java  FileStatus   / /tmp/id /autoexec.bat
---/---
Canonical name C:
File is readable.
File is writable.
Last modified Thu Jan 01 00:00:00 GMT 1970
It's a directory

---/tmp/id---
file not found

---/autoexec.bat---
Canonical name C:AUTOEXEC.BAT
Parent directory: 
File is readable.
File is writable.
Last modified Fri Sep 10 15:40:32 GMT 1999
File size is 308 bytes.

As you can see, the so-called " canonical name” not only includes a leading directory root of C: , but also has had the name converted to uppercase. You can tell I ran that on MS-Windows. On Unix, it behaves differently:

$ java FileStatus / /tmp/id /autoexec.bat
---/---
Canonical name /
File is readable.
Last modified October 4, 1999 6:29:14 AM PDT
It's a directory

---/tmp/id---
Canonical name /tmp/id
Parent directory: /tmp
File is readable.
File is writable.
Last modified October 8, 1999 1:01:54 PM PDT
File size is 0 bytes.

---/autoexec.bat---
file not found

$

On a typical Unix system there is no autoexec.bat file. And Unix filenames (like those on a Mac) can consists of upper- and lowercase characters: what you type is what you get.