gistfile1.java

private void show_tags(CompoundTag ctag, Player player) {
  ctag.keySet().forEach(new Consumer<String>() {
    @Override
    public void accept(String s) {
      player.notice("S: " + s + " V: " + ctag.get(s).toString());
    }});
  }
}

// And later...

TileEntity tile_entity = the_block.getTileEntity();
CompoundTag ctag = tile_entity.getDataTag();

ctag.put("CustomName", "FARTAHONTAS");
ctag.put("CustomNameVisible", true);

tile_entity.writeToTag(ctag);

tile_entity.update();
the_block.update();

ctag = the_block.getTileEntity().getDataTag();

player.notice("After Write");
show_tags(ctag, player);