Java: Example - Recursive List

// RecusiveList -- Recursively list directories and files
// Fred Swartz 1997-08-06 (Bangkok, Thailand)
//     revised 2000-10-31 (Rota, Spain)

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

public class RecursiveList {
    static final int      maxDepth = 20;  // max 20 levels (directory nesting)
    static final String[] indent   = new String[maxDepth];  // array of indents.
    static final String   indentString = "   ";             // single indent.
    
    //===================================================================== main
    public static void main(String[] args) {
        indent[0] = indentString;
        for (int i = 1; i < maxDepth; i++) {
           indent[i] = indent[i-1] + indentString;
        }
        
        String root = (args.length>0) ? args[0] : System.getProperty("user.dir");
        File start = new File(root);
        if (start != null && start.isDirectory()) {
            listDirContents(start, 0);
        }else{
            System.out.println("Not a directory: " + args[0]);
        }
    }//end main
    
    
    //========================================================== listDirContents
    public static void listDirContents(File someDirectory, int depth) {
        if (depth > maxDepth) return;
        String[] fileOrDirName = someDirectory.list(); // list of files and dirs
        Arrays.sort(fileOrDirName);
        for (int i = 0; i < fileOrDirName.length; i++) {
            System.out.println(indent[depth] + fileOrDirName[i]); // print it
            File f = new File(someDirectory, fileOrDirName[i]);
            if (f.isDirectory()) {
                listDirContents(f, depth+1); // Recursively list contents of dir
            }
        }
    }//endmethod listDirContents
    
}//endclass