In general, yes. All of the Hawaiian islands have very limited public transportation, with the exception of Waikiki (on Oahu). If you’re planning to fly into Honolulu, stay in Waikiki and hit up the beaches and major tourist attractions around there, you can get away with not having a car of your own, or rent one for just a few days of your trip. However, if you're traveling to another island or want to explore other areas of Oahu outside of Waikiki, you'll need a rental car.