[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

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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

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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

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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

 

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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

 

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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

 

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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