I usually stay in Waikiki during my trips to Hawaii and drive by the Ala Moana courts quite a bit, and the courts consistently seem very active. Haven't played tennis there myself but I always wondered about how people play with all the random spurts of light showers that pass through even on hot summer days, but that doesn't seem to stop the locals. Based on how chill and friendly people are, I'm pretty sure you can just go into the major public courts and they'd be willing to hit with you. Hope you enjoy your trip!
Can you expand on this? I'm going to a conference in Waikiki later this year and would love to play in the evenings. Is this at the Diamond Head Tennis Center or the Kapi'olani Regional Park Tennis Courts, or somewhere else? What days do they play & do I just show up bringing my racket and a can of balls?