How to get immidiate disk-usage of a directory

[adnan]

Is there something similar to Java's File.length() method? I would like to know 
the immediate disk usage for a directory.
    
    
    A (1K)
    | -> B (3k)
    | -> C (9k)
    
    
    Run

Here, directory A's immediate disk usage is 1k. What proc provides me this 
information?

(Reference Java solution):
    
    
    public static long diskUsage(File root) {
        long total = root.length();
        if (root.isDirectory()) {
            for (String childname: root.list()) {
                File child = new File(root, childname);
                total += diskUsage(child);
            }
        }
        return total;
    }
    
    
    Run