Java Final Keyword

The final keyword allows us to prevent same thing defining again or modifying later in the program.

Uses of final keyword

The keyword final has 3 uses for making

1. Final Variable
2. Final Methods
3. Final Classes

1. Final Variable

By declaring a variable with final keyword the access is restricted for making inheritable. The value of final variable never be changed in the program. They always behave like a class variables and they do not take any space on indivisual object of the class.

Syntax

final type variable_name = constant_value;

Example

final int max = 300;

Program Example

Program to show use of final variables in the program.

class Base
{
    final int max = 300;
    Base()
    {
       max = 400;    // produces an error   
    }
}

class Derived extends Base
{
    Derived()
    {
       max = 500;    // produces an error
    }
    
    public static void main(String args[])
    {
       Derived d1 = new Derived();
    }
}
	

Output

In above program we have declared final variable as max in the Base class. We have tried to change the value of it inside the Base class as well in derived class, Produces same error.

2. Final Methods

The method which is defined as final it ensures that the functionality defined in the method will never be changed.

Syntax

final type method_name()
{
    ...
    ...
}

Example

final int show()
{
    final method code
    ...
}

Program Example

class Base
{
    final void display()
    {
        System.out.println("I'm from base class");
    }
}

class Derived extends Base
{
    void display() // produces an error
    {
        System.out.println("I'm from Derived class");
    }
    public static void main(String args[])
    {
        Derived d1 = new Derived();
        d1.show();
    }
}
	

Output

In above example, we have declared the display method as final in the Base class. When we tried to redefine in the Child class then we get an error.

3. Final Class

To prevent the classes being further subclasses is called as a final class. It is Necessary for the security reasons in java.

Syntax

final class className
{
     ...
     ...   
}

Example

final class First
{
    ...
    ...
}

Program Example

final class Base
{
    void Message()
    {
        System.out.println("I'm from base class");
    }
}

class Derived extends Base // produces an Error
{
    void Message()
    {
        System.out.println("I'm from Derived class");
    }
    public static void main(String args[])
    {
        Derived d1 = new Derived();
        d1.Message();
    }
}
	

Output