Final Keyword in Java

Usage of final Keyword

• Use of final keyword with variables to stop value change
• Use of final keyword with methods to stop method overriding
• Use of final keyword with class to stop inheritance

How to initialized final Variable

It is necessary to initialize a final variable. otherwise, the compiler will raise a compile-time error. An initializer or assignment statement may only be used once to initialize a final variable.

• When a final variable is declared, it can be initialized. The most typical strategy is this one. If a final variable is not initialized during declaration, it is referred to as a blank final variable. The two methods for initializing a blank final variable are listed below.
• An instance-initializer block or the constructor can both initialize a blank final variable. If your class has multiple constructors, it must be initialized in each one in order to avoid a compile-time error.
• A static block can initialize a final static variable that is empty.

1. Use of final keyword with variables

When a variable is declared with the final keyword, its value is unchangeable; it is effectively a constant. This also implies that a final variable must be initialized.
If a final variable is a reference type (such as an object or an array), it cannot be rebound to point to a different object. However, you can still modify the internal state of the object that the final variable references. This means you can add or remove elements from an array or collection that is declared as final.
It is best to represent final variables in all uppercase, with underscores used to separate words.

Above concept is explained in below program

final int num = 5; // Declaring a final variable of type int
final String message = "Hello"; // Declaring a final variable of type String

final int[] numbers = {1, 2, 3}; // Declaring a final array
final List<String> names = new ArrayList<>(); // Declaring a final collection

names.add("Ram"); // Modifying the internal state of the final collection
numbers[0] = 10; // Modifying the first element of the final array
System.out.println(num); // Output: 5
System.out.println(message); // Output: Hello
System.out.println(Arrays.toString(numbers)); // Output: [10, 2, 3]
System.out.println(names); 

5
Hello
[10, 2, 3]
[Ram] 

Java program uses of final keyword with variables

class Nano{  
	final int speedlimit=90;// it is final variable  
	void run(){  
	  speedlimit=400;  // can't reassign value
	}  
	public static void main(String args[]){  
		Nano obj=new  Nano();  
	    obj.run();  
	}  
}

Exception in thread "main" java.lang.Error: Unresolved compilation problem: 
                                            The final field Nano.speedlimit cannot be assigned 

2. Use of final keyword with methods

A method is referred to as a final method if the keyword final is used in its declaration. An ultimate method cannot be changed. This is done by the Object class, which has a few final methods. Methods that must have the same implementation across all derived classes must be declared with the final keyword.

class vehicles{
	final void run(){
		System.out.println("Running");
	}
}

class Nano extends vehicles{  
	void run(){   // Cannot override the final method from vehicles
	  System.out.println("Running");
	}  
	public static void main(String args[]){  
		Nano obj=new  Nano();  
	    obj.run();  
	}  
}

Compile Time Error 

3. Use of final keyword with class

A class is referred to as a final class if the keyword final is used in its declaration. There is no way to extend a final class (inherited).

final class vehicles{}

    class Nano extends vehicles{   // The Nano class cannot be subclass the final class vehicles
	void run(){   
	  System.out.println("Running");
	}  
	public static void main(String args[]){  
		Nano obj=new  Nano();  
	    obj.run();  
	}  
}

Compile Time Error 

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