is… / has…Boolean getters answer a yes/no question. The Java convention is to name them like the question they answer — isAdult(), not getAdult().
isAvailable(), isDirty(), isAdult(), hasReservation(), canCheckIn(). Most start with is for a state, has for ownership/possession, occasionally can for capability. The Java compiler doesn't care — it's a convention — but every Java codebase you'll join uses it.