Its 'final' Keyword

Lets discuss one of the important keyword final that appears in java.final can be used with respect to variables,methods and class.

final with respect to variables:

A variable that is declared s a final acts like a constant variable and do not entertain any further modifications.

Example

import java.io.*;
class Code
{
 final int var=10;
 void methodA()
 {   
 var=15;
 System.out.println(var);
 } 

 public static void main(String args[])
 { 
  Code c=new Code();
  c.methodA();
 }
}

Output:

Code.java:6: error: cannot assign a value to final variable var
 var=15;
 

Initialization of final variables:

A final variable that is not initialized at the time of declaration is called a blank final variable. We can only initialize such variables inside the constructor of the class.

Example:

import java.io.*;
class Titans
{
 final int var;
 Titans()
 { 
  var=10;
 }
  void methodA()
 {
  System.out.println("value of var is "+var);
 }
}
class Code
{
 public static void main(String args[])
 {
  Titans t=new Titans();
  t.methodA();  
 }
}

Output:

value of var is 10

A final variable that is declared as a static final and didn't get initialized at the time of the declaration,then it must be initialized only in the static block.

Example:

import java.io.*;
class Code
{
 static final int var;
 static{
 var=20;}
 public static void main(String args[])
 {
  Code c=new Code();
  System.out.println("value of var is "+c.var);  
 }
}

Output:

value of var is 20

final with respect to methods:

A method prefixed with final cannot be overridden.

Example:

import java.io.*;
class Code
{
 final void methodA()
 {
  System.out.println("This methodA() is in class Code");
 }
}
class Titans extends Code
{ 
 void methodA()
 { 
  System.out.println("This methodA() is in class Titans");
 }
 public static void main(String args[])
 { 
  Titans t=new Titans();
  t.methodA();
 }
}

Output:

Titans.java:11: error: methodA() in Titans cannot override methodA() in Code
 void methodA()

final with respect to class:

Whenever a class is declared as final it cannot be inherited.

Example:

 import java.io.*;
final class Code
 {
  int var=10;
 } 
 class Titans extends Code
 { 
 public static void main(String args[])
 { 
  Titans t=new Titans();
  System.out.println(t.var);
 }
}

Output:

Titans.java:6: error: cannot inherit from final Code
 class Titans extends Code