Simple guide on using Final keyword in Java

Welcome to your simple guide to the final keyword in Java. In this article, we'll cover everything from final variables and methods to advanced topics like final classes and inheritance.

Whether you're a beginner or an experienced Java programmer, this article will provide you with the knowledge and skills you need to effectively use the final keyword in your code. Let's dive in!

Table of Contents

  1. Introduction to the final keyword

  2. final variables and final methods

  3. final classes and using final in inheritance

  4. Best practices for using final

  5. Conclusion

Introduction to the final keyword

The final keyword is used to define entities that cannot be modified after their initial assignment. The final keyword can be applied to variables, methods and classes.

What it means in basic terms is that when we create a variable with the final keyword and assign it a value,its value cannot be changed.

Similarly, when a method is declared as final, it cannot be overridden by any subclass. And when a class is marked as final, it cannot be extended by any subclass.

final int numberOfEyes = 2; //initialize a varible and declare it as final
numberOfEyes = 3; //This will throw as error saying numberOfEyes is final and cannot be changed.

The main purpose of the final keyword is to enforce immutability and prevent unintended modification of variables, methods and classes in a program.

Another important of using the final keyword is to improve the performance of the program because the compiler knows that the variable’s value will not change during execution and it will optimize the code while ensuring that the method and classes marked as final maintain consistent behavior throughout the program.

final variables and final methods

One of the benefits of using the final keyword is that it improves code clarity. By marking a variable as final it shows that we are not interested in changing its value anywhere in the program which means it’s a constant value. While marking a method as final helps to prevent modification of the method behavior ensuring it is consistent throughout the program.

class FinalSample {
    static final double pi = 3.14;

    public static void main(String[] args) {
        double radius = 5.0;
        double area = areaOfCirle(radius);
        System.out.println("The area of the circle with radius " + radius + " is " + area);

    public static final double areaOfCirle(double radius) {
        // Area = πr²
        return pi * radius * radius;

However, having a variable mark as final will prevent the data type from changing anywhere in the program. Also when methods are marked as final it prevents them from being flexible on a program.

final classes and Using final in inheritance

In other to prevent a class from being extended by another class, mark the class as final. Once a class is declared as final, it cannot be modified or extended and all its methods and variables are implicitly final.

Best practices for using final

  1. Use final for constants: final is often used to declare constants in Java. A constant is a value that does not change during the execution of a program. By declaring a variable as final, you ensure that it cannot be modified after its initial assignment

  2. Use final for method parameters: You can also use final to declare method parameters. This can help prevent unintended modification of the method's input parameters, making the code more robust.

  3. Use final for local variables: Declaring local variables as final can make your code more readable and self-documenting. It also ensures that the value of the variable cannot be changed after initialization.

  4. Declare final classes: If a class is not intended to be subclassed, it should be declared as final. This prevents unintended inheritance and ensures that the class behaves as expected.

  5. Avoid declaring final fields without initializing them: Declaring a final field without initializing it can lead to bugs and unexpected behavior. Make sure to initialize the final fields when they are declared.

    Here are some common mistakes to avoid when using final:

    1. Using final unnecessarily: While using final can make your code more robust, overusing it can make your code harder to read and understand. Use the final judiciously and only when it is necessary.

    2. Using final fields as mutable objects: Declaring an object reference as final does not prevent the object from being modified. If you declare a reference to a mutable object as final, make sure that the object itself is immutable, or that you are not modifying the object.

    3. Declaring final on private methods: Declaring a private method as final has no effect, as private methods are not inherited by subclasses.

    4. Declaring variables as final in loops: Declaring variables as final in loops can lead to unexpected behavior, as the variable value is not updated during each iteration of the loop.


we've covered everything you need to know about the final keyword in Java. We've explored how to use final for variables, methods, and classes, and how it can help enforce immutability and improve code safety. We've also discussed best practices for using final and common mistakes to avoid.

We hope that you found this guide helpful, and we encourage you to continue to learn and explore the many features of Java. Don't forget to practice and apply what you've learned to your code, and good luck on your programming journey!

Thanks for reading.

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