Every interisland flight that I've gone on has had the same security access as any other flight. So, if you can't bring it into the terminal on a normal flight, you wouldn't be able to bring it on the short one either. That said, I haven't been to the smaller terminal from which many interisland flights take off. I wouldn't count on it being any different though.
For laws in Honolulu (might be statewide), I did some searching a few months ago and here's what I came up with: no butterfly knives, autos, gravity knives, or other assorted weapons (brass knuckles, slung shot, etc.). No blade length seemed to be specified. Assisted seems to be okay. Fixed blades that are considered daggers or dirks are banned except for diving knives. I would imagine that context counts for that one ("Yes officer, this is a diving knife." "Yeah, you were walking down a sidewalk in downtown in a suit and tie. Good luck at court.")
All this is from what I could find. Hope it helps and if someone sees that I'm wrong, please correct me! Have a wonderful trip (when the time comes)! Volcanoes National Park is a glorious place to be because you can see where the islands came from. There are also things there that you won't be able to see literally anywhere else in the world. On both Oahu and the Big Island, don't be afraid to try new things (food especially) and meet new people. Hawaii's cultural beauty is in its diversity and while there are bad apples, there are also people who still carry that "aloha" spirit.
