Java Cookbook

Listing a Directory

Problem

You need to list the filesystem entries named in a directory.

Solution

Use a java.io.File object’s list( ) method.

Discussion

The java.io.File class contains several methods for working with directories. For example, to list the filesystem entities named in the current directory, just write:

String names = new File(".").list(  )

This can become a complete program with as little as the following:

/** Simple directory lister.
 */
public class Ls {
    public static void main(String argh_my_aching_fingers[]) {
        String[] dir = new java.io.File(".").list(  ); // Get list of names
        java.util.Arrays.sort(dir);        // Sort it (Data Structuring chapter))
        for (int i=0; i<dir.length; i++)
            System.out.println(dir[i]);    // Print the list
    }
}

Of course, there’s lots of room for elaboration. You could print the names in multiple columns across the page. Or even down the page, since you know the number of items in the list before you print. You could omit filenames with leading periods, as does the Unix ls program. Or print the directory names first; I once used a directory lister called lc that did this, and I found it quite useful. By constructing a new File object for each name, you could print the size of each, as per the DOS dir command or the Unix ls -l command (see Section 10.2). Or you could figure out whether each is a file, a directory, or neither. Having done that, you could pass each directory to your top-level function, and you’d have directory recursion (the Unix find command, ...