What does the final keyword do in Java?

Final has three uses: 1) Final variable cannot be reassigned after initialization (constant). For objects, the reference is final but object state can change. 2) Final method cannot be overridden by subclasses, ensuring consistent behavior. 3) Final class cannot be extended (e.g., String, Integer). Benefits: thread safety (immutable variables), security (prevent overriding), optimization (JVM can inline final methods). Use for constants (static final), preventing inheritance, and ensuring method behavior.