This example implements methods that recursively visits all files and directories under a directory. 
    // Process all files and directories under dir
    public static void visitAllDirsAndFiles(File dir) {
        process(dir);
    
        if (dir.isDirectory()) {
            String[] children = dir.list();
            for (int i=0; i<children.length; i++) {
                visitAllDirsAndFiles(new File(dir, children[i]));
            }
        }
    }
    
    // Process only directories under dir
    public static void visitAllDirs(File dir) {
        if (dir.isDirectory()) {
            process(dir);
    
            String[] children = dir.list();
            for (int i=0; i<children.length; i++) {
                visitAllDirs(new File(dir, children[i]));
            }
        }
    }
    
    // Process only files under dir
    public static void visitAllFiles(File dir) {
        if (dir.isDirectory()) {
            String[] children = dir.list();
            for (int i=0; i<children.length; i++) {
                visitAllFiles(new File(dir, children[i]));
            }
        } else {
            process(dir);
        }
    }