Final Keyword in Java

February 10, 2023

Final Keyword

In this article we will be discussing about Final Keyword in Java.

The Final keyword is used to initialize Constant variables and many more. We can use final with variables, methods and classes.

Final :

The Final keyword is kind of a constant keyword in c++, just like constant, in Java Final keyword is used to initialize constant declaration after which their values can’t be changed throughout the program.

We can initialize following declarations with the help of final keyword:

variable
method
class

Final Variable:

You can declare any final variable using “final” Keyword. you’ll not be able to change this value afterwards throughout the program i.e final variable once initialized with a value can’t be change furthermore.

final int str = "PrepInsta";

Keywords and Variables

Data types

JVM vs JRE vs JDK

Type Conversion

How a code runs in Java

Note What if we try to change the value of the final variable after declaring it.

Run

import java.util.*;

public class Main{
    // class definition 
    class Prepster{

        // defining final variable
        final int test = 10;
        void change(){
            test = 20;
        }

    public static void main(String[] args){
        // Initializing the class object 
        prepster obj = new prepster();
        obj.change();
    }
}

Output:

Compile Time Error

In Java, a final variable is a variable that once assigned a value, its value cannot be changed. Attempting to change the value of a final variable will result in a compile-time error.
This code will result in a compile-time error with the message: “error: cannot assign a value to final variable test”.

Final Function:

If you are using the final keyword with the method in java, you will not be able to override in the program.

Run

import java.util.*;

// Definition of the class
class Lakshit{
    // Final method in java
	final void test(){
       System.out.print("final Function");
    }
}
public class Main{	
    public static void main(String[] args){
		// Initializing the class object
        Lakshit obj = new Lakshit();
		
		// Function calling with the help of class object
        obj.test();
    }
}

Output:

final Function

Explanation In the above Example, the Lakshit class has a final method named test. We create an instance of the Lakshit class and then call the test method on that instance. When the test method is called, the message "final function" is printed to the console.

Java Final Class:

if we use Final keyword with class, we’ll not be able to extend it.

Run

import java.util.*;

// final Class definition 
final class test {
	// function definition
    void run(){
        System.out.println("test class called");
    }
}

public class Main{      
    public static void main(String[] args){ 
		//Initializing the object of the final class
        test obj = new test();  
		
		// Calling the run function of final class
        obj.run();  
    }  
}

Output:

test class called

Explanation In the above Example, the test class is defined with the final keyword. We create an instance of the test class and then call the run method on that instance. When the run method is called of the final test class, the message "test class called" is printed to the console.

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