Learn Kotlin - Data Class


Data Class

We frequently create a class to do nothing but hold data. In such a class some standard functionality is often mechanically derivable from the data. In Kotlin, this is called a data class and is marked as data.

Example

In Java


public class Developer {

    private String name;
    private int age;

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

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

        Developer developer = (Developer) o;

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

    }

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

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

In Kotlin


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

When we mark a class as a data class, you don’t have to implement or create the following functions like we do in Java.

  • hashCode()
  • equals()
  • toString()
  • copy()

The compiler automatically create these internally, so it also leads to clean code.

Although, there are few requirements that data classes need to fulfil:

  • The primary constructor needs to have at least one parameter.
  • All primary constructor parameters need to be marked as val or var
  • Data classes cannot be abstract, open, sealed or inner.

So whenever you get these situations, use data class.