Java: What are Records in Java and why were they introduced?

Record — immutable data carrier class (Java 14+). Reduces boilerplate for simple data objects.

Key features:

• Immutable by default — all fields are final.
• Auto-generates: constructor, getters, equals(), hashCode(), toString().
• Cannot extend classes (implicitly extends java.lang.Record).
• Can implement interfaces.
• Can have static fields and methods.
• Fields are declared in the header, not in the body.
• The generated getters are named after the field (e.g., name() not getName()).

Complete example:

1public record Person(String name, int age) {
2    // Canonical constructor auto-generated
3    // name() and age() getters auto-generated
4    // equals(), hashCode(), toString() auto-generated
5}
6
7// Usage
8Person p = new Person("Alice", 25);
9String name = p.name();  // getter
10int age = p.age();       // getter
11System.out.println(p);   // Person[name=Alice, age=25]
12
13// Records are immutable
14Person p2 = p.withName("Bob");  // creates new instance

Why it matters:

• Before Records, creating a DTO required 50+ lines of boilerplate code.
• Records reduce this to a single line.
• Immutability is guaranteed — no accidental mutations.
• Perfect for use in Sets and as Map keys (proper equals/hashCode).

Common mistakes:

• Trying to add setters (Records are immutable).
• Trying to extend another class (implicitly extends Record).
• Using getters with get prefix (use name() not getName()).

When to use:

• DTOs (Data Transfer Objects).
• Value objects.
• Tuple-like classes.
• Keys in Maps.

When NOT to use:

• Mutable objects.
• Classes needing inheritance.
• Complex business logic with mutable state.