String text = "TEST1234TEST";

String hiddenText = "";
for(char c : text.toCharArray()){
 hiddenText += "§" + c;
}

//String hiddenText = "§T§E§S§T§1§2§3§4§T§E§S§T";

ItemStack is = new ItemStack(Material.STONE);
ItemMeta itemMeta = is.getItemMeta();
itemMeta.setDisplayName(hiddenText);
is.setItemMeta(itemMeta);

Bukkit.broadcastMessage(hiddenText.replace("§", ""));
Bukkit.broadcastMessage(itemMeta.getDisplayName().replace("§", ""));