What are data classes in Kotlin?

Overview

Data classes automatically generate common methods for data-holding classes.

Syntax

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data class User(val name: String, val age: Int)

Auto-Generated Methods

1. Constructor

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val user = User("Alice", 25)

2. Getters

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println(user.name) // Alice
println(user.age)  // 25

3. equals() and hashCode()

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val user1 = User("Alice", 25)
val user2 = User("Alice", 25)
println(user1 == user2) // true

4. toString()

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println(user) // User(name=Alice, age=25)

5. copy()

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val user1 = User("Alice", 25)
val user2 = user1.copy(age = 26)
// user2 = User("Alice", 26)

6. componentN()

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val (name, age) = user
println(name) // Alice
println(age)  // 25

Comparison with Java

Java (50+ lines)

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public class User {
    private String name;
    private int age;
    // Constructor, getters, equals, hashCode, toString
}

Kotlin (1 line)

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data class User(val name: String, val age: Int)

Requirements

• Primary constructor must have at least one parameter
• Parameters must be
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  val

  or
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  var

• Cannot be
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  abstract

  ,
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  open

  ,
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  sealed

  , or
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  inner

Use Case: Perfect for models, DTOs, and value objects.