j21-record-members - Blog of Vincent VAUBAN

✨ Explicit Declaration of Record Class Members
with French Actor Flair

Java record classes provide a compact syntax for declaring immutable data carriers. But you’re not just limited to the default behavior: you can explicitly define many of the derived members.
Let’s illustrate with a theme: French actors. 🎬
🎭 Custom Accessor Method
You can explicitly define accessor methods that Java otherwise generates automatically. Here's a record for an actor with a custom name() method:

record FrenchActor(String name, int birthYear) { // Custom accessor method for 'name' public String name() { System.out.println("Accessing name: " + name); return name; } }

💡 Reminder: If you redefine accessors, they must match the auto-generated versions: same name, return type, and be public.
Similarly, if you implement your own versions of the equals, hashCode, and toString methods, then ensure that they have the same characteristics and behavior as those in the java.lang.Record class, which is the common superclass of all record classes.

🧮 Static Members in Record Classes
Record classes can include static fields, methods, and static initializers. For example, let’s track the average French actor's debut age:

record FrenchActor(String name, int birthYear) { // Static field static int averageDebutAge; // Static initializer static { averageDebutAge = 22; } // Static method public static FrenchActor createYoungDebut(String name) { int estimatedYear = java.time.Year.now().getValue() - averageDebutAge; return new FrenchActor(name, estimatedYear); } }

❌ What’s Not Allowed in Records
Unlike normal classes, record classes cannot:
🟣 Declare instance (non-static) fields outside of the header.
🟣 Use instance initializers.
🚫 The following is invalid and won’t compile:

record FrenchActor(String name, int birthYear) { // ❌ This is illegal in a record BiFunction<Integer, Integer, Integer> ageCalculator; { ageCalculator = (now, year) -> now - year; } }

📦 Instance Methods and Nested Types
Even though records are mostly about data, you can still add behavior via instance methods. You can also nest types, including other record classes!
Here's an example where we calculate how old an actor will be in a specific year, and use a nested record for movie awards:

record FrenchActor(String name, int birthYear) { // Nested record class record Award(String title, int year) {} // Instance method public int ageInYear(int year) { return year - birthYear; } // Example usage public Award winAward(String title, int awardYear) { return new Award(title, awardYear); } }

🧬 Final Notes
✅ You can declare instance methods and static members.
✅ You can nest classes, including other records.
❌ You cannot declare native methods in record classes.

🎬 Summary with a French Twist

var marion = new FrenchActor("Marion Cotillard", 1975); System.out.println(marion.name()); // Custom accessor System.out.println("Age in 2025: " + marion.ageInYear(2025)); var award = marion.winAward("César", 2005); System.out.println(award); // Nested record usage

Record classes are great for modeling simple data structures—like information about your favorite French actors—while still letting you define useful logic and structure where needed.

✨ Explicit Declaration of Record Class Members

Java record classes provide a compact syntax for declaring immutable data carriers. But you’re not just limited to the default behavior: you can explicitly define many of the derived members.

Let’s illustrate with a theme: French actors. 🎬

🎭 Custom Accessor Method

You can explicitly define accessor methods that Java otherwise generates automatically. Here's a record for an actor with a custom name() method:

💡 Reminder: If you redefine accessors, they must match the auto-generated versions: same name, return type, and be public.

Similarly, if you implement your own versions of the equals, hashCode, and toString methods, then ensure that they have the same characteristics and behavior as those in the java.lang.Record class, which is the common superclass of all record classes.

🧮 Static Members in Record Classes

Record classes can include static fields, methods, and static initializers. For example, let’s track the average French actor's debut age:

❌ What’s Not Allowed in Records

Unlike normal classes, record classes cannot:

🟣 Declare instance (non-static) fields outside of the header.

🟣 Use instance initializers.

🚫 The following is invalid and won’t compile:

📦 Instance Methods and Nested Types

Even though records are mostly about data, you can still add behavior via instance methods. You can also nest types, including other record classes!

Here's an example where we calculate how old an actor will be in a specific year, and use a nested record for movie awards:

🧬 Final Notes

✅ You can declare instance methods and static members.

✅ You can nest classes, including other records.

❌ You cannot declare native methods in record classes.

🎬 Summary with a French Twist

Record classes are great for modeling simple data structures—like information about your favorite French actors—while still letting you define useful logic and structure where needed.