• Definitions:
  • A file is a coherent collection of information that can be identified by a name
  • A file system is a method for storing and organizing files
  • A directory (or folder) is a group of files and/or directories
• Examples:
  • MS-Windows: FAT and NTFS
  • OS X: HFS Plus
  • CD-ROM: ISO 9660

• The File and Files Classes:
  • A File object is an encapsulation of a file/directory handle (not an actual file on the file system)
  • The Files class is a utility class for operating on File and Path objects
• Important Concepts:
  • The working directory is named "." (and it's parent is named "..")
  • Absolute (starting with a '/' in UNIX, ':' or ":\" in MS-Windows, and "\\" for UNC) and Relative Pathnames
  • The Separator Character ('/' on UNIX, '\' on MS-Windows)
  • The Path-Separator Character (':' on UNIX, ';' on MS-Windows)
• Constructing a File Object:
  • File(java.lang.String)
  • File(java.lang.String, java.lang.String)

• Checking Attributes:
  • File.canRead()
  • File.canWrite()
  • File.exists()
  • File.isDirectory()
  • File.isFile()
  • File.isHidden()
  • File.lastModified()
• Modify Attributes:
  • File.renameTo(java.io.File)
  • File.setReadOnly()
  • File.setLastModified(long)

• Creating:
  • A directory can be created using File.mkdir()
  • A file is created by writing to it
• Deleting:
  • File.delete()
• Working with Directories:
  • File.list() returns a String[]
  • File.listFiles() returns a File[]

An Example

javaexamples/iobasics/Dir.java

import java.io.*;


/**
 * An implementation of a simple directory listing utility.
 *
 * @author  Prof. David Bernstein, James Madison University
 * @version 1.0
 */
public class Dir
{
    /**
     * The entry point of the application.
     *
     * @param args  The paths to list
     */
    public static void main(String[] args)
    {
        if ((args == null) || (args.length == 0))
        {
            dir(".");
        }
        else
        {
            for (int i=0; i<args.length; i++)
            {
                dir(args[i]);
            }
        }
    }

    /**
     * Print (to standard out) a simple listing of the contents of the
     * given directory.
     *
     * @param path  The path to the directory of interest
     */
    private static void dir(String path)
    {
        File    wd;
        File[]  list;        
        
        wd   = new File(path);
        if (wd.isDirectory())
        {
            list = wd.listFiles();
            System.out.printf("Contents of %s\n", wd.getAbsoluteFile());

            for (int i=0; i<list.length; i++)
            {
                System.out.printf("%-50s %10d\n", 
                                  list[i].getName(), list[i].length());
            }
        }
        else
        {
            System.out.printf("%s is a file.\n", wd.getAbsoluteFile());
        }
        System.out.printf("\n");
    }
}
        

• Copying:
  • Files.copy(java.nio.file.Path, java.nio.file.Path, java.nio.file.CopyOption...)
• Creating Links and Symbolic Links:
  • Files.createLink(java.nio.file.Path, java.nio.file.Path)
  • Files.createSymbolicLink(java.nio.file.Path, java.nio.file.Path, java.nio.file.attribute.FileAttribute...)