Kotlin Data Classes vs Regular Classes vs Java Records

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Boilerplate Reduction

// Example class definition
class User(val id: Int, val name: String, val email: String)
// This class compiles fine, but if you check for equality:
val u1 = User(1, "Alice", "alice@example.com")
val u2 = User(1, "Alice", "alice@example.com")
println(u1 == u2) // false

Even though the contents are identical, these are different object instances. So the equality check will return false. But if we define as data class, the equality check will return true. Because data classes are checking the value based equality.

Auto Generated Functions

Mutability vs. Immutability

class Item(var name: String, var price: Double)

data class Item(val name: String, val price: Double)

Immutable data structures help prevent unexpected side effects — especially useful in threaded or reactive systems.

Kotlin Data Classes vs. Java Records

Java Records are introduced with Java 16 and it brought a similar concept to Java to declare immutable data holders.

public record User(int id, String name, String email) {}

• equals()
• hashCode()
• toString()
• Accessor methods (id(), name(), email())

Kotlin data classes and Java records common features

• They both are data holders.
• Provide automatically generated utility methods.
• Defaultly immutable (fields are implicitly final in Java records and val in Kotlin).
• Improve readability and reduce boilerplate.

User u1 = new User(1, "Alice", "alice@example.com");
User u2 = new User(1, "Alice", "alice@example.com");
// And check for equality
System.out.println(u1.equals(u2)); // true

Just like Kotlin data classes, the equality is based on field values in Java Records.

Differences of Kotlin Data Classes and Java Records

Kotlin:

// Data class definition
data class User(val id: Int, val name: String, val email: String)
// copy method usage
val updatedUser = User(1, "Alice", "alice.new@example.com")
val copiedUser = updatedUser.copy(name = "Alice Updated")
println(copiedUser)  // User(id=1, name=Alice Updated, email=alice.new@example.com)

Java:

// Record definition
public record User(int id, String name, String email) {}

User updatedUser = new User(1, "Alice", "alice.new@example.com");
// No copy() method; manual reconstruction:
User copiedUser = new User(updatedUser.id(), "Alice Updated", updatedUser.email());
System.out.println(copiedUser);

• You need mutable or immutable data objects.
• You want easy object copying or destructuring.
• You’re building Android apps, Kotlin Multiplatform projects, or lightweight models.

• You’re working in a Java 16+ environment.
• You need immutable DTOs with concise syntax.
• You don’t need copying or destructuring.

Both Kotlin data classes and Java records move developers toward immutable, declarative data modeling, reducing clutter and focusing on readability and correctness.

Comparisation Table

That is all.

Burak Hamdi TUFAN