[Java] Final keyword

 Final keyword

- It in java is used to restrict the user

- Stop Value Change

- Stop Method Overridding

- Stop Inheritance

1. How to use

- final keyword can be applied with the variables, a final variable that have no value it is called blank final variable or uninitialized final variable

- blank final variable

a. It can be initialized in the constructor only

b. It can be static also which will be initialized in the static block only

2. Final variable

public class Student { final int grade = 100; void run(){ grade = 90; } public static void main(String[] args){ Student aa = new Student(); aa.run(); } }

Complile time error

- Final variable once assigned a value can never be changed

3. Final method

class Teacher{ final void run(){ System.out.println("Teacher"); } } public class Student extends Teahcer{ void run(){ System.out.println("Student"); } public static void main(String[] args){ Student aa = new Student(); aa.run(); } }  

Complile time error

- It cannot override it

4. Final class

final class Teacher{ final void run(){ System.out.println("Teacher"); } } public class Student extends Teacher{ public static void main(String[] args){ new Student().run(); } }  

Complile time error

- You cannot extend it

5. Question

1) Is final method inherited?

- final method is inherited but you cannot override

2) What is blank or uninitialized final variable?

- A final variable that is not initialized at the time of declaration is known as blank final variable

- It can be initialized only in constructor

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

3) static blank final variable

- A static final variable that is not initialized at the time of declaration is known as static blank final variable

- It can be initialized only in static block

 class A{ static final int data; static{ data = 50; } public static void main(String[] args){ System.out.println(A.data); } }

4) What is final parameter?

- You cannot change the value of final it

 class A{ int cube(final int n){ n = n +2; } public static void main(String[] args){ A aa = new A() aa.cube(5); } }

Complile time error

5) Can we declare a constructor final?

- No, because is never inherited