final Java Keyword with Examples

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As we know that inheritance enables us to reuse existing code, sometimes we do need to set limitations on extensibility for various reasons; the final keyword allows us to do exactly that.

In this short article, we’ll take a look at what the final keyword means for classes, methods, and variables - 

1. The final keyword may be applied to a variable, indicating the value of the final variable can not be changed (It will be constant).
2. The final keyword may be applied to a class, indicating the class may not be extended (subclassed).
3. The final keyword may be applied to a method, indicating the method may not be overridden in any subclass

A final variable that has no value it is called blank final variable or uninitialized final variable. It can be initialized in the constructor only. The blank final variable can be static also which will be initialized in the static block only.

Let's discuss usage of a final keyword with respect to variable, method, and class.

Java final variable

If you make any variable as final, you cannot change the value of a final variable(It will be constant).

Example of final variable

The below diagram demonstrates that the final variable name can't be reassigned which will result in compile time error.

Java final method

The final keyword may be applied to a method, indicating the method may not be overridden in any subclass.

When we design a class and feel that a method shouldn’t be overridden, we can make this method final. We can also find many final methods in Java core libraries.

Sometimes we don’t need to prohibit a class extension entirely, but only prevent overriding of some methods. A good example of this is the Thread class. It’s legal to extend it and thus create a custom thread class. But its isAlive() methods is final.

Java final method example

The below diagram demonstrates that the final method can't be overridden which will result in compile time error:

Java final class

The final keyword may be applied to a class, indicating the class may not be extended (subclassed).

If we look at the code of Java core libraries, we’ll find many final classes there. For example String, Wrapper classes and BigDecimal, BigInteger etc.

Java final class example

The below diagram demonstrates that the final class can't be extended which will result in compile time error.

What is blank or uninitialized final variable?

A final variable that is not initialized at the time of declaration is known an as a blank final variable.

If you want to create a variable that is initialized at the time of creating an object and once initialized may not be changed, it is useful. For example PAN CARD number of an employee.

It can be initialized only in the constructor.

Example of blank final variable

class Student{  
    int id;  
    String name;  
    final String PAN_CARD_NUMBER;  
...  
}  

Note that the final PAN_CARD_NUMBER variable not initialized. We can initialize a blank final variable only in a constructor.

Summary

1. Variables marked as final can’t be reassigned.
2. Methods marked as final cannot be overridden.
3. Classes marked as final can’t be extended.

All Java Keywords 

1. abstract Java Keyword
2. assert Java Keyword
3. boolean Java Keyword
4. break Java Keyword
5. byte Java Keyword
6. case Java Keyword
7. catch Java Keyword
8. char Java Keyword
9. class Java Keyword
10. continue Java Keyword
11. default Java Keyword
12. do Java Keyword
13. double Java Keyword
14. else Java Keyword
15. enum Java Keyword
16. extends Java Keyword
17. final Java Keyword
18. finally Java Keyword
19. float Java Keyword
20. for Java Keyword
21. if Java Keyword
22. implements Java Keyword
23. import Java Keyword
24. instanceof Java Keyword
25. int Java Keyword
26. interface Java Keyword
27. long Java Keyword
28. native Java Keyword
29. new Java Keyword
30. package Java Keyword
31. private Java Keyword
32. protected Java Keyword
33. public Java Keyword
34. return Java Keyword
35. short Java Keyword
36. static Java Keyword
37. strictfp Java Keyword
38. super Java Keyword
39. switch Java Keyword
40. synchronized Java Keyword
41. this Java Keyword
42. throw Java Keyword
43. throws Java Keyword
44. transient Java Keyword
45. try Java Keyword
46. void Java Keyword
47. volatile Java Keyword
48. while Java Keyword