For Final Keyword,

The final modifier can be applied to four Java constructs:

1. variables: a final variable can be set once and only once.
2. fields: a final field can also be set only once, by the constructor of the class which defines it.
3. methods: a final method cannot be overridden nor hidden.
4. classes: a final class cannot be extended.

Notice how using final is an entirely negative act. The final keyword works by subtracting, limiting default language mechanisms: the ability to override a method, to set a variable or a field. The motivations behind using final fall into three broad categories: correctness, robustness, and finally performance.

--kamal.