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Final Modifier

Final Modifier:-Final is a modifier in java and this modifier is applicable for variable, method and class. Final modifier is used for restricting to change. Using this modifier we can declare final variable, final method and final class.
If variable is declared as a final then cannot change the value or cannot reassign the value of final variable.
If method is declared as a final then that method cannot redefine by the child classes or child classes cannot override final methods.
If class is declared as a final then that class cannot inherit.

Example1:-final variable (Customer.java)

class Customer
{
final int accNo;
 }

Output:-

C:\JAVATECH>javac Customer.java
Customer.java:3: error: variable accNo not initialized in the default constructor
final int accNo;
          ^
1 error

Example2:-

class Customer
{
final int accNo;
Customer()
{
accNo=101;
}
}

Output:-         (code compiles fine)

C:\JAVATECH>javac Customer.java
C:\JAVATECH>


Example3:-


class Customer
{
final int accNo;
Customer()
{
accNo=101;
}
public static void main(String[]args)
{
Customer c=new Customer();
System.out.println("Account No. is  "+c.accNo);
}
}

Output:-

C:\JAVATECH>javac Customer.java
C:\JAVATECH>java Customer
Account No. is  101


Example4:-


class Customer
{
final int accNo;
Customer()
{
accNo=101;
accNo=200;
}
public static void main(String[]args)
{
Customer c=new Customer();
System.out.println("Account No. is"+c.accNo);
}
}

Output:-

C:\JAVATECH>javac Customer.java
Customer.java:7: error: variable accNo might already have been assigned
accNo=200;
^
1 error

Example5:-

class Customer
{
final int accNo=101;

public static void main(String[]args)
{
Customer c=new Customer();
System.out.println("Account No. is  "+c.accNo);
}
}

Output:-

C:\JAVATECH>javac Customer.java
C:\JAVATECH>java Customer
Account No. is  101


Example6:-Final class example (Customer.java)

final class Bank
{
}
class Customer extends Bank
{
}

Output:-

C:\JAVATECH>javac Customer.java
Customer.java:5: error: cannot inherit from final Bank
class Customer extends Bank
                       ^
1 error


Example7:-


final class Bank
{
void m1()
{
System.out.println("Bank facility provided ");
}
}
class Customer //extends Bank
{
public static void main(String[]args)
{
Bank b=new Bank();
b.m1();
}
}

Output:-

C:\JAVATECH>javac Customer.java
C:\JAVATECH>java Customer

Bank facility provided


Example8:- final method example

class Bank
{
final void getBalance()
{
System.out.println("Your balance is ");
}
}
class XBank extends Bank
{
void getBalance()
{
System.out.println("Overriding getBalance");
}
}

Output:-

C:\JAVATECH>javac Customer.java
Customer.java:14: error: getBalance() in XBank cannot override getBalance() in Bank
void getBalance()
     ^
  overridden method is final
1 error

Example9:-


class Bank
{
void m1()
{
System.out.println("Bank facility provided ");
}
final void getBalance()
{
System.out.println("Your balance is by final method");
}
}
class XBank extends Bank
{
void m1()
{
System.out.println("Bank facility provided by XBank ");
}
}
class Customer
{
public static void main(String[]args)
{
XBank b=new XBank();
b.m1();
b.getBalance();
}
}

Output:-

 C:\JAVATECH>javac Customer.java
C:\JAVATECH>java Customer
Bank facility provided by XBank

Your balance is by final method
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