Jo, you can also request a "pitcher" of OJ to keep in a mini-fridge if your cabin has one. The Zenith did not when we were on her but that was at least 5 years ago. Put out your Room Service card for breakfast each evening before your retire requesting your juice at whatever time you will require it. You can ask for as many glasses as you wish with no extra charge. But, be sure to tip the server, as it may not be your cabin steward and you probably won't see the same person again. Juice is usually available at the self-serve stations on the buffet and at table service in the main dining room during meals. I often bring an insulated sports water bottle and fill it with juice & alchol, lemonade, iced tea etc. to enjoy out by the pool.
Bon Voyage