private void saveUsers() throws IOException {
        if (file_store != null) {
            try {
                file_store.store(new FileOutputStream(file_path), "");
            } catch (Exception e) {
                throw new IOException(e);
            }
        }
    }
private void saveUsers ( ) throws IOException { if ( file_store != null ) { try { file_store . store ( new FileOutputStream ( file_path ) , "" ) ; } catch ( Exception e ) { throw new IOException ( e ) ; } } }
Save user lists to the file on the disk

@throws IOException if fail to save to file