public ArrayList<String> getFileNames(){
	System.out.println("getting all files with reads per transcripts counts. Files names finish with " + fnamePattern);
        ArrayList<String> file_names = new ArrayList<String>();
        File dir = new File(dirName);
        for (File ch : dir.listFiles()) {
            if (ch.isDirectory())
                for (File child : ch.listFiles()){
                   if ( (child.getName().equals(fnamePattern)) ){
                       file_names.add(child.getPath());
                  }
            }
        }
         return file_names;
    }