public void build(String prefix, File dir) {
	File[] files = dir.listFiles();
	// Consider every file in the current directory
	for (File file : files) {
	    if (file.isDirectory()) {
		// It's a directory, so make a recursive call into the directory
		if (DEBUG) System.out.println("directory: " + prefix+file.getName());
		build(prefix+"/"+file.getName(),file);
	    } else {
		// It's a file, so add it to the HashMap
		if (DEBUG) System.out.println("     file: " + prefix+file.getName());
		hm.put(prefix+"/"+file.getName(),file);
	    }
	}
    }