Java Record vs Final Class: A Comparison

In Java, there are different ways to define classes with specific characteristics and behaviors. Two such options are Java Records and Final Classes. While they serve different purposes, they both have their own benefits and use cases. In this article, we will explore the differences between Java Records and Final Classes and understand when to use each of them.

Introduction to Java Records

Java Records were introduced in Java 14 as a new language feature to provide a concise way of declaring classes that are primarily used to store data. Records are immutable by default, meaning their state cannot be modified after instantiation. They automatically generate useful methods such as constructors, equals(), hashCode(), and toString(), based on the fields defined within the record.

Let’s look at an example of a Java Record:

public record Person(String name, int age) {
}

In the above example, we defined a Person record with two fields: name of type String and age of type int. The Person record automatically generates a constructor, equals(), hashCode(), and toString() methods based on these fields.

Understanding Final Classes

On the other hand, Final Classes are classes that cannot be subclassed. When a class is declared as final, it means it cannot be extended further. Final Classes are often used to prevent inheritance, ensuring that the class remains intact without any modifications from subclasses.

Let’s see an example of a Final Class:

public final class MathUtils {
    public static int add(int a, int b) {
        return a + b;
    }
}

In the above example, we defined a MathUtils class as final, which means it cannot be extended. The MathUtils class provides a static method add() to perform addition.

Key Differences

1. Purpose and Usage

Java Records are primarily used to define classes that serve as simple data containers. They provide a concise way of declaring classes with default implementations of common methods like equals(), hashCode(), and toString(), making them suitable for representing data objects.

Final Classes, on the other hand, are used when you want to explicitly prevent inheritance. By declaring a class as final, you ensure that it cannot be extended, thereby enforcing the integrity and intended behavior of the class.

2. Mutability

Java Records are immutable by default, meaning their state cannot be modified after instantiation. The fields defined within a record are final and cannot be reassigned. This immutability ensures that the data stored in records remains consistent and avoids accidental modification.

Final Classes, on the other hand, can be mutable or immutable based on how they are implemented. The final keyword only prevents the class from being subclassed, but it does not enforce immutability. You can have mutable fields and methods within a final class.

Let’s see an example of a mutable Final Class:

public final class Counter {
    private int count;

    public void increment() {
        count++;
    }

    public int getCount() {
        return count;
    }
}

In the above example, the Counter class is declared as final, but it contains a mutable field count and a method increment() to modify the count.

3. Auto-generated Methods

One of the key features of Java Records is the automatic generation of commonly used methods. These include the constructor, equals(), hashCode(), and toString(). The auto-generated methods provide a standardized way of working with records and eliminate the need for manual implementation.

Let’s look at an example of using a Java Record:

Person person1 = new Person("John", 25);
Person person2 = new Person("John", 25);

System.out.println(person1.equals(person2)); // true
System.out.println(person1.hashCode() == person2.hashCode()); // true
System.out.println(person1.toString()); // Person[name=John, age=25]

In the above example, we created two Person records with the same name and age. The equals() method automatically compares the values of the fields and returns true if they are equal. The hashCode() method generates a hash code based on the field values, ensuring that equal records have the same hash code. The toString() method returns a string representation of the record.

Final Classes do not have any auto-generated methods. You have full control over the implementation of constructors, equality checks, and other methods in a final class. You need to manually write these methods based on your requirements.

1. Extensibility

Java Records cannot be extended or subclassed. They are implicitly final and do not allow inheritance. This limitation is intentional to maintain the integrity of the record’s data and behavior.

Final Classes, as the name suggests, explicitly prevent subclassing. By declaring a class as final, you ensure that it cannot be extended, providing a clear indication of the class’s intended design and preventing modifications by subclasses.

When to Use Java Records and Final Classes

Use Java Records when you need a lightweight data container with automatic implementations of common methods. Records are ideal for representing simple data objects, such as DTOs (Data Transfer Objects), where immutability and consistent behavior are desired.

Use Final Classes when you want to explicitly prevent subclassing and ensure that a class remains intact without any modifications. Final Classes are useful when you want to create utility classes, helper classes, or classes that should not be extended for architectural or security reasons.

Conclusion

In this article, we explored the differences between Java Records and Final Classes. Java Records provide a concise way of defining data containers with default implementations of common methods, making them suitable for representing data objects. Final Classes, on the other hand, prevent inheritance and ensure the integrity of the class. Understanding these differences will help you choose the appropriate approach based on your specific requirements and design goals.