Final Keyword in Java: A Complete Guide to Using the final Modifier

Have you ever wondered how to make your variables, methods, or even entire classes unchangeable in Java? The solution lies in a single keyword – the Final Keyword in Java. This versatile modifier plays a critical role in preventing modifications, ensuring stability, and securing your code from unwanted changes. 

In this blog, we'll dive deep into the multiple uses of the Final Keyword in Java. From locking down variables and methods to creating non-extendable classes, we'll explore how this keyword can make your programs more robust. Ready to learn more about how ‘final’ can safeguard your code? Let’s explore the magic behind this powerful keyword! 

Table of Contents 

1) What is the Final Keyword in Java? 

2) Key Features of the Final Keyword in Java 

3) Java Final Variable 

4) Java Final Method 

5) Java Final Class 

6) Advantages of Using the Final Keyword in Java 

7) Conclusion 

What is the Final Keyword in Java? 

In Java, the Final Keyword is used to ensure immutability and restrict modifications. It is applicable to classes, methods, and variables. This modifier is especially useful for enhancing security, improving performance, and ensuring the stability of core components in Java programs. 

The Final Keyword in Java can be used in many contexts. The ‘final’ can be: 

a) A `final` variable becomes a constant that cannot be changed once assigned 

b) A `final` method prevents overriding in subclasses, ensuring consistent behaviour 

c) A `final` class cannot be subclassed, safeguarding its functionality
 

Key Features of the Final Keyword in Java 

Here are the key features of the Final Keyword in Java that make it essential for ensuring stability, security, and performance in your code: 

a) Immutability: When a variable is declared as final, its value cannot be changed after it has been initialised.  

b) Prevention of Method Overriding: Declaring a method as final prevents subclasses from overriding it, ensuring consistent behaviour.  

c) Restricting Inheritance: Declaring a class as final prevents other classes from inheriting from it, which is essential when you want to secure core functionality. 

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1) Java Final Variable 

In Java, a final variable can only be initialised once, and after that, its value cannot be changed. This property makes final variables a good fit for constants in Java. You can declare final variables at class level (static final) or within methods (local final variables). 

Syntax:
 

Example of Java Final Variable 

Example:
 

Output:

1) Static Final Variable (MAX_SPEED): Declared as `public static final`, meaning it belongs to the class, is a constant, and can be accessed directly as `FinalVariableExample.MAX_SPEED`. Its value remains unchanged once initialised. 

2) Local Final Variable (speedLimit): Declared as `final` inside the `displayMaxSpeed()` method, meaning it cannot be modified after initialisation. It holds a constant value of 100 and is printed each time the method is called. 

3) Main Method: Creates an instance of `FinalVariableExample`, calls `displayMaxSpeed()` to print "Speed Limit: 100", and then prints the static final variable `MAX_SPEED` as "Max Speed: 120". 

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2) Java Final Method 

The final method in Java cannot be overridden by subclasses. This ensures that the specific method implementation remains unchanged in any derived class, providing stability in the behaviour of methods that must not be altered by subclassing. 

Syntax: 
 

Example of Java Final Method 

Example: 

Output:

Explanation: 

a) The ‘run()’ method in the ‘Vehicle’ class is marked as ‘final’, which means that subclasses, such as ‘Car’, are not allowed to override it. 

b) Attempting to override the ‘run()’ method in the ‘Car’ class would result in a compilation error. 

c) In the ‘main’ method, when we create an instance of ‘Car’ and call ‘myCar.run()’, it will execute the ‘run()’ method from the ‘Vehicle’ class, as it cannot be overridden. 

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3) Java Final Class 

When a class is declared as final, it cannot be subclassed. This means no other class can inherit from a final class, making it useful in cases where you want to restrict inheritance for security or design reasons. 

Syntax:
 

Example of Java Final Class 

Example:
 

Output:

Explanation: 

a) The ‘Calculator’ class is marked as ‘final’, which means no other class can extend it. If you try to create a subclass (e.g., ‘AdvancedCalculator’), it will result in a compilation error. 

b) The method ‘add()’ inside the ‘Calculator’ class can be used normally, but no new behaviour (such as overriding or additional methods) can be introduced through inheritance. 

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Advantages of Using the Final Keyword in Java 

Here are the key advantages of using the Final Keyword in Java, which enhances the security, performance, and maintainability of your code: 

a) Improved Performance: The Final Keyword can lead to performance optimisations. Since the value of a final variable doesn’t change, the Java compiler can make certain assumptions that result in more efficient code execution.  

b) Security: Declaring classes and methods as final provides a security mechanism by ensuring that sensitive methods cannot be overridden and that core functionality is preserved.  

d) Design Intent: Using the final clearly communicates to Java Developers that a class or method is intended to remain unchanged. It makes the code more readable and easier to maintain by preventing unnecessary or accidental modifications.  

e) Immutability: The Final Keyword helps create immutable objects in Java, which is a cornerstone of functional Programming and multi-threaded environments. Immutable objects can be shared safely between threads without the risk of data corruption.  

f) Thread Safety: Final fields make objects thread-safe by ensuring that their values remain consistent across different threads. This is particularly beneficial in concurrent programming. 

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Conclusion 

The Final Keyword in Java is a game-changer for Developers seeking to create stable, secure, and high-performance code. Locking down variables, methods, and classes brings both clarity and control to your programs. Embrace the power of ‘’final’ and elevate your Java Development! 

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