What is the purpose of "data class"?

Question

In Kotlin it is possible to create a class as follows:

data class Dragon(private val name: String, val glass: Int)

What is the main objective of the data class in Kotlin? When should we use?

Answer 1

Also called registration, is to be a simple structure basically with data, without behaviors, other than those necessary for the basic infrastructure of the language, as a comparison (equals()), hash (hashCode()), access methods for defined fields (compatible with Java Beans), copy (copy()) and stringification (toString()), beyond the builder, of course. So we usually say that she is POD (Plain Old Data).

Cannot inherit from data classes. Syntax is greatly simplified:

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

It would be more or less the same as doing in Java:

public class User {
    private String name;
    private int age;

    public User() {
        this.name = "";
        this.age = 0;
    }

    public User(String name) {
        this.name = name;
        this.age = 0;
    }

    public User(int age) {
        this.name = "";
        this.age = age;
    }

    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public String component1() { //para acesso posicional e deconstrução
        return name;
    }

    public int component2() {
        return age;
    }

    public User copy() {
        return new User(name, age);
    }

    public User copy(String newName) {
        return new User(newName, age);
    }

    public User copy(int newAge) {
        return new User(name, newAge);
    }

    public User copy(String newName, int newAge) {
        return new User(newName, newAge);
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        User user = (User) o;

        if (age != user.age) return false;
        return name != null ? name.equals(user.name) : user.name == null;
    }

    @Override
    public int hashCode() {
        int result = name != null ? name.hashCode() : 0;
        result = 31 * result + age;
        return result;
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

I put in the Github for future reference.

Isn’t it wonderful? This is foreseen in C#, it’s just not known when, it was supposed to be since version 6. In C# it’s even more complex.

It is possible to have extra behaviors in the class and can extend (not in the sense of inheritance) as a normal class.

Documentation.

See more in What is the difference between Kotlin data class and Scala case class?.