The final keyword in Java

 This article explains the usage of final keyword with simple example.
  The final keyword in java is used to restrict the user .There are mainly 3 uses of the keyword final.
1)final can be used to define constants.
2)final can be used to prevent inheritance.
3)final can be used to prevent method overriding.

Let us discuss one by one with example
1) final can be used to define constants.

Syntax :
final data_type variable_name=value;

class FinalConst { final int a=10; void Display() {System.out.println("Value of a ="+a); } } public class FinalEx { public static void main(String[] args) { FinalConst FinalConstObj=new FinalConst(); FinalConstObj.Display(); } }

Output:

  In the example the variable a is declared with final i.e constant . If you try to assign a value to the variable it will not accept and will error out. Please refer the below example .

class FinalConst { final int a=10; void Display() {System.out.println("Value of a ="+a); } void ChangeConst() { a=25; } } public class FinalEx { public static void main(String[] args) { FinalConst FinalConstObj=new FinalConst(); FinalConstObj.ChangeConst(); FinalConstObj.Display(); } }

Error:

2)final can be used to prevent inheritance
final class FinalConst { final int a=10; void Display() {System.out.println("Value of a ="+a); } } public class FinalEx extends FinalConst { public static void main(String[] args) { System.out.println("Prevents Inheritance"); } }  

Error:

We have created class FinalConst as final and tried to inherit that class in the class FinalEx.

3)final can be used to prevent method overriding.
class FinalConst { void Display() {System.out.println("It is a method in parent class "); } final void FinalDisplay() {System.out.println("It is a final method in parent class"); } } class FinalMethodtest extends FinalConst { void Display() {System.out.println("It is a method override in child class "); } final void FinalDisplay() {System.out.println("It is a final method ovverride in subclass class"); } } public class FinalEx { public static void main(String[] args) { FinalMethodtest obj1=new FinalMethodtest(); obj1.Display(); } }

Error:

We have tried to override the method FinalDisplay() in child class which is final method in parent class.