Final Class in Java – Tutorial with Examples

In Java, the ‘final’ keyword restricts the usage of classes, methods, and variables. When applied to a class, the ‘final’ keyword makes it impossible for the class to be subclassed. In simple words, no other class can inherit from a final class, ensuring that the class’s functionality remains unchanged and is not overridden. This article explains the final class in Java in depth.

Introduction to Final Class in Java

The concept of inheritance is fundamental to object-oriented programming in Java. It allows a class to inherit properties and behaviours (fields and methods) from another class. However, There are situations where you might want to prevent a class from being extended or modified. This is where the ‘final’ keyword comes into play. A class declared ‘final’ in Java cannot be subclassed, meaning no other class inherits from it.

We can use Java’s final keyword to create a final class. This class definition should be complete and not abstract. Here is the syntax for creating the final class.

Syntax:

In Java, we can define the final class using the final keyword by implementing the before-the-class keyword. The following source defines a class with two instance variables and one display method. Now, we create the object of the Vehicle class and call it the displayDetails method, which prints the model and brand.

The following program demonstrates the “how to use final class”:

Program

Output

Java Final Variables

We can also use the final keyword to define the variables. Once initialised, a ‘final’ variable’s value cannot be changed. This property makes the ‘final’ variable useful for defining constants and ensuring their values remain constant throughout the program’s execution.

Let’s see “how we can declare the final keyword in Java before the variables’ type.

The following program demonstrates the final variables:

Program

Output

Java Final Methods

In Java, the ‘final’ keyword can be applied to methods to indicate that subclasses cannot override them. When a method is declared ‘final’, no class that extends the current class can provide a different implementation. This is particularly useful to ensure that certain behaviour defined in a superclass remains consistent and cannot be altered by subclasses.

• Inheritance: A ‘final’ method cannot be overridden by any subclass.
• Usage: It ensures that the method’s implementation remains the same across all subclasses, guaranteeing its behaviour.
• Design: It can prevent the modification of critical methods that are essential to a class’s integrity.

The following program demonstrates the final method in Java:

Program

Output

Advantages of Final Class

In Java, the ‘final’ keyword can be used with classes to prevent them from being subclassed. Here are some key advantages of using a ‘final’ class.

• Security: Marking a class as ‘final’ ensures that other classes cannot extend or modify it. It is particularly useful for securing critical parts of an application or library where you want to prevent unauthorised or potentially harmful modifications.
• Integrity: By making a class ‘final’, We can ensure that the implementation remains consistent and unaltered. This can be important for classes that provide fundamental or standardised functionality, where modification could lead to unexpected behaviour or bugs.
• Simplicity: The class is ‘final’. It simplifies the class hierarchy by preventing further subclassing. This can make the source code easier to understand and maintain, as developers can be sure that the class’ behaviour is not altered through inheritance.
• Thread Safety: Immutable classes are inherently thread-safe. By making a class ‘final’, We can help ensure that its instances are immutable and thus safe to use in concurrent programming scenarios.

Also Check: Java Tutorial for Beginners

Disadvantages of Final Class

The final class has some advantages and disadvantages. Here’s a list of the disadvantages of the final class.

• Inflexibility in Extensibility: This prevents other classes from extending or inheriting the final class, limiting the ability to add or modify functionality.
• Difficulty in Testing and Mocking: It makes it challenging to mock or stub final classes in unit tests, especially with frameworks that rely on inheritance.
• Limitation in Design Patterns: It cannot be used in design patterns that require inheritance, such as the template method pattern, reducing design options.
• Minimal Performance Gains: While final classes can offer slight performance optimisations, the benefits are often minimal compared to the loss of flexibility.

Conclusion

In Java, a final class is a powerful feature that helps maintain the integrity of your software code. By declaring a class as ‘final’, you ensure that no other class can extend it, which can be crucial for classes that handle sensitive operations or are integral to a critical library.

This restriction helps secure the class’s functionality and allows the JVM (Java Virtual Machine) to optimise performance, as it knows the class’s implementation will not be altered through inheritance. Furthermore, using ‘final’ classes simplifies design and implementation by minimising inheritance-related issues, thereby reducing the need for extensive testing and debugging.