j21-record-features - Blog of Vincent VAUBAN

🎬 Java Record ClassesFeaturing Famous French Actors

In Java, record classes offer a concise, readable way to define immutable data structures—like casting actors for roles with a fixed script: no improvisation allowed!

🧑‍🎤 Record Classes Are Final (Like Legendary Performances)Record classes are implicitly final. That means:🟣 You can’t extend them.🟣 But they can be generic, implement interfaces, and be annotated just like normal classes.Let’s explore these features using a cinematic theme.

🌟 Example 1: A Generic Record – AwardedActorWe want to record information about an actor and their Oscar prize. We'll make it generic to support different date formats.

record AwardedActor<T extends Temporal>(
    String name,
    int numberOfOscars,
    T awardedDate
) { }

🎭 Imagine:
AwardedActor<LocalDate> marion = new AwardedActor<>("Marion Cotillard",
 1, 
LocalDate.of(2008, 2, 24));

Here, Marion Cotillard won her Oscar in 2008 for La Vie en Rose.
We use generics to support different types of dates (LocalDate, ZonedDateTime, etc.).

🎞️ Example 2: A Record Implementing an Interface – Actor implements StarWe define a Star interface for anyone who shines on screen:

interface Star {
    String catchPhrase();
}

Now let’s implement this in a record:

record Actor(String name, int popularity) implements Star {
    @Override
    public String catchPhrase() {
        return "Lights, camera, " + name + "!";
    }
}

Example:
Actor omar = new Actor("Omar Sy", 95);
omar.catchPhrase() 👉 "Lights, camera, Omar Sy!"

Even though records are compact, they can still carry behavior.

🕰️ Example 3: Annotated Record – MovieWe want to ensure our movies have a valid duration and a proper release date. Let's define a custom annotation:

import java.lang.annotation.*;

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface ValidDuration { }

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface NotInTheFuture { }

Now let's define the Movie record:

record Movie(
    String title,
    @NotInTheFuture LocalDate releaseDate,
    @ValidDuration int durationMinutes
) { }

🎬 Example:
new Movie("The Intouchables", LocalDate.of(2011, 11, 2), 112);

What Does This Translate To Behind the Scenes?This annotated record:

record Movie(@NotInTheFuture LocalDate releaseDate, @ValidDuration int durationMinutes) { }

Is roughly equivalent to this normal class:

public final class Movie {
    private final @NotInTheFuture LocalDate releaseDate;
    private final @ValidDuration int durationMinutes;

    public Movie(LocalDate releaseDate, int durationMinutes) {
        this.releaseDate = releaseDate;
        this.durationMinutes = durationMinutes;
    }

    public LocalDate releaseDate() { return this.releaseDate; }
    public int durationMinutes() { return this.durationMinutes; }
}

➡️ The annotations apply to the fields thanks to @Target(ElementType.FIELD).

🎯 Recap – Records with a Touch of Glamour

🎬 Java Record Classes

In Java, record classes offer a concise, readable way to define immutable data structures—like casting actors for roles with a fixed script: no improvisation allowed!

🧑‍🎤 Record Classes Are Final (Like Legendary Performances)

Record classes are implicitly final. That means:

🟣 You can’t extend them.

🟣 But they can be generic, implement interfaces, and be annotated just like normal classes.

Let’s explore these features using a cinematic theme.

🌟 Example 1: A Generic Record – AwardedActor

We want to record information about an actor and their Oscar prize. We'll make it generic to support different date formats.

Here, Marion Cotillard won her Oscar in 2008 for La Vie en Rose.We use generics to support different types of dates (LocalDate, ZonedDateTime, etc.).

🎞️ Example 2: A Record Implementing an Interface – Actor implements Star

We define a Star interface for anyone who shines on screen:

Now let’s implement this in a record:

Even though records are compact, they can still carry behavior.

🕰️ Example 3: Annotated Record – Movie

We want to ensure our movies have a valid duration and a proper release date. Let's define a custom annotation:

Now let's define the Movie record:

What Does This Translate To Behind the Scenes?

This annotated record:

Is roughly equivalent to this normal class:

➡️ The annotations apply to the fields thanks to @Target(ElementType.FIELD).

🎯 Recap – Records with a Touch of Glamour

Here, Marion Cotillard won her Oscar in 2008 for La Vie en Rose.
We use generics to support different types of dates (LocalDate, ZonedDateTime, etc.).