What is the point of "final class" in Java?

java

oop

inheritance

design-patterns

byAlex Kataev·Oct 16, 2024

A final class in Java is a class that cannot be extended, ensuring its methods and behavior remain unchangeable. This promotes an immutable design which can lead to easier-to-understand, safer, and more reliable code. Here's a concise example:

public final class Constants {
    // Even Superman can't change this
    public static final String ERROR_MSG = "Operation not supported";
    // Other awesome, immutable contents of this class
}

When Constants is marked as final, you can trust its values and intentions remain consistent as no subclass can alter its static message or extend its functionality.

Deep Dive: "Final" Class Benefits

Security through Inalterability

Declaring a class as final is often a security measure. It assures that a wily programmer cannot sneak in and add a subclass that corrupts the original class's intended behavior. As solid as a rock, a final class proves to be a steady cornerstone in your codebase.

Optimization Dream

Arriving in the guise of efficiency, final classes allow compilers, akin to helpful elves, to make assumptions and inline methods to optimize the performance. Your code just got a nitro boost!

Clarity in Design

Utilizing a final class sends a clear signal to other developers: this class is complete, it doesn't need anything else. Forget about extensions, this class is ready to roll as-is. This is often the case for utility classes filled with static methods.

Practical Applications of "Final" Class

Crafting Immutable Classes

One of the most common scenarios for employing a final class is when crafting immutable classes. You can work with instances of the class, confident that none of their sneaky subclasses will change their state.

// As constant as a mother's love
public final class ImmutableLove {
    private final String loveMessage = "Always and Forever";
    
    public String getLoveMessage() {
        return loveMessage;
    }
    // No, you can't change the love message. It's final.
}

Denoting the End of Inheritance

Sometimes, your class is the end of the line - it doesn't need a junior! A final class enforces this and keeps the inheritance hierarchy tidy and trimmed.

public final class TheFarewell {
    // That's all, folks!
}

Simplicity in Structure

Forget about complex inheritance trees. A final class helps you establish a clean, easy-to-follow class structure. The KIS ("Keep it simple") principle at its finest!

Invariant Security

If you've got a class with invariants, let final be your bodyguard. Make sure no one breaks the rules!

Puzzle Integrity

The final keyword keeps your puzzle intact. No piece can be added or adjusted to change the original image. The integrity of your picture remains the same!

Simple Elegance

Declaring a final class simplifies your code's complexity while maintaining its elegance. It's like a finished puzzle, providing an easily understandable, cohesive entity.

Just a friendly reminder though, while final classes can't be extended, they can still extend others. They are not the 'black sheep' of OOP family.

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