j21-record-canonical - Blog of Vincent VAUBAN

🎬 Canonical Constructor
– The Long Way
We begin with a record named FrenchActor. We want to ensure that no actor has a negative number of awards. Here's how we could write this using a canonical constructor (with full parameter declaration):

record FrenchActor(String name, int cesarAwards) { public FrenchActor(String name, int cesarAwards) { if (cesarAwards < 0) { throw new IllegalArgumentException( String.format("Invalid number of César Awards for %s: %d", name, cesarAwards)); } this.name = name; this.cesarAwards = cesarAwards; } }

Here, we are manually repeating the record components in the constructor signature and assigning them to fields. It works, but it’s verbose and repetitive.

🎬 Compact Constructor – The Elegant Way
To simplify things, records let us declare a compact constructor. The parameter list is implied, and the assignments to fields are done automatically:

record FrenchActor(String name, int cesarAwards) { public FrenchActor { if (cesarAwards < 0) { throw new IllegalArgumentException( String.format("Invalid number of César Awards for %s: %d", name, cesarAwards)); } } }

This version is cleaner, avoids repetition, and still performs the same validation logic. It's ideal when you want to keep things concise.

🍿 Example Usage
Let’s create a few actors:

var danyBoon = new FrenchActor("Dany Boon", 0); var isabelleHuppert = new FrenchActor("Isabelle Huppert", 2); var invalidActor = new FrenchActor("Unknown Star", -1); // Throws exception

✅ Summary
🟣 Use a canonical constructor if you need full control and explicit field assignment.
🟣 Prefer a compact constructor in records to keep the code clean and readable.
🟣 Validation logic works identically in both.

🎬 Canonical Constructor

– The Long Way

Here, we are manually repeating the record components in the constructor signature and assigning them to fields. It works, but it’s verbose and repetitive.

🎬 Compact Constructor – The Elegant Way

To simplify things, records let us declare a compact constructor. The parameter list is implied, and the assignments to fields are done automatically:

This version is cleaner, avoids repetition, and still performs the same validation logic. It's ideal when you want to keep things concise.

🍿 Example Usage

Let’s create a few actors:

✅ Summary

🟣 Use a canonical constructor if you need full control and explicit field assignment.

🟣 Prefer a compact constructor in records to keep the code clean and readable.

🟣 Validation logic works identically in both.