Using the "final" modifier whenever applicable in Java

java

immutability

best-practices

thread-safety

byAnton Shumikhin·Nov 21, 2024

In Java, the keyword final acts like a wall, forbidding alteration to variables, parameters, and fields. When you declare something as final, you're communicating that it's a constant or it should not change after its initial assignment. This reinforces the principle of immutability which is critical for thread safety and predictability in larger codebases. Here's a quick glimpse:

public class ImmutablePoint {
    private final int x;
    private final int y;

    public ImmutablePoint(int x, int y) {
        this.x = x;
        this.y = y;
    }
    // There are no setters; x and y are like the laws of physics - unchangeable!
}

In essence, using final tells others that it's the developer's firm intention for these values to remain unchanged. This boosts your code's readability and maintainability.

Applying 'final': Where and why

Solidifying objects

When crafting objects that don't mutatepost-construction — a mainstay of functional programming — 'final' is your golden ticket. Declaring class fields as final is like coding in stone; ensuring the immutability of an object.

Enums over constants

Ditch your army of static final fields in favour of enums for a more organized, type-safe alternative. Enums are like Sunday school kids — well-formed and reliably constant.

Architectural iron-cladding

final classes and methods prevent meddling in subclasses. It's like laying down the law when designing APIs or frameworks; guarding base functionalities against unwanted extensions.

Signalling intentions

By marking variables and method parameters as final, you not only forbid reassignments, but also clarify intentions. It's a sort of 'hands-off, this is my variable' sign.

Interacting with inner classes

Fancy tinkering with local variables from an inner class? You'll need to declare them as final. This makes for consistent behaviour, even across different code scopes.

Mindful use

While 'final' could be the secret sauce to super readable code, handle with care! Using final relentlessly, without adding clarity or enforcing intent, just leaves verbiage in its wake.

Getting hands-on with 'final'

Boosting reliability

Using final not only signals your intentions to the compiler but also guards against accidental slip-ups. It's like your code is wearing an invincible shield, boosting the reliability.

Consistency in Template Methods

In the template method pattern, making the overarching method final leads to a firm sequence of steps while individual steps can be customized by subclasses. It’s like having a fixed recipe but with toppings of your choice.

Thread-safe and Secure

final fields are implicitly thread-safe. Once set, they don't change. It's like an ancient prophecy, immune to the high winds of multithreading.

Compiler's Best Friend

The Java compiler and the JVM get a kick out of the immutability of final variables and may take advantage of this to perform a few optimizations.

Potential Flexibility Bottleneck

While it has its charm, imposing final everywhere might make your code rigid and less flexible. It's a fine balance between establishing security and not turning your classes into programming Stonehenge. Use final judiciously.

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