Final Keyword in Java

The Final keyword in Java allows us to set limitations on accessibility to a code i.e it adds a restriction to access.

The static keyword can be used in the following context :

1. Final Variable : to create constants
2. Final Method : to prevent method overriding
3. Final Class : to prevent inheritance

1. Java final variable

When a variable is declared with final keyword, its value can’t be modified, essentially, a constant. A final variable can be assigned value later, but only once

When to use a final variable :
final variables must be used only for the values that we want to remain constant throughout the execution of program.

Example:

              
public class FinalVariableClass {

    // a final variable direct initialization
    final int NUMBEROFITEMS = 5;

    // a blank final variable
    final int CART_CAPACITY;

    // an another blank final variable
    final int  MINIMUM;

    // a final static variable with direct initialization
    static final String COMPANY_NAME = "ProgrammerToday";

    // a  blank final static  variable
    static final double TEST_CONSTANT;

    // instance initializer block for initializing CART_CAPACITY
    {
        CART_CAPACITY = 10;
    }

    // static initializer block for initializing TEST_CONSTANT
    static{
        TEST_CONSTANT = 1.1;
    }

    // constructor for initializing MINIMUM
    // Note that if there are more than one
    // constructor, you must initialize MINIMUM
    // in them also
    public FinalVariableClass()
    {
        MINIMUM = 1;
    }

public static void main(String args[])
{
// re-assigning final variable will throw compile-time error
COMPANY_NAME = "ProgrammerToday_new";
}

}

2. Java final method

A Final method cannot be overridden

In a scenario where you feel that you method should not be overridden. So that it does not change your piece of code.

Example:

class A {
    final void display(){
        System.out.println("display method of parent class");
    }
 }
 
class B extends A{
 
    //'display()' cannot override 'display()' in 'A'; overridden method is final
    void display(){
        System.out.println("display method of child class");
    }
 
 } 
  

3. Java final class

A final class cannot be extended(inherited).

There are 2 uses of making a class final:

Example:

1. Is to prevent inheritance as the final class cannot be extended. e.g : wrapper classes like Integer, Float etc.

  final class FinalClass {
  }
  
  // The following class is not correct.
  class B extends FinalClass
  {
     // COMPILE-ERROR! Cannot inherit from final 'FinalClass'
  }
  

2. Is to make the class immutable for example like String.

FAQ , Questions and Answers

Q1. Can we initialize blank final variable ? If yes, then How ?

Sol. There are two ways to initialize blank final variable:

1. Using constructor
2. Using initialization block

Refer to the example above.

Q2. Can we declare a constructor as final ?

Sol. No, because it is never inherited.

Summary

In this article we learnt about Java Final Keyword and its various use cases. We saw it can be used as a variable, method and a class.
Hope you liked the article !

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