Kotlin Data Class

Kotlin Data Class: In this tutorial, you will learn to create data classes in Kotlin. You will likewise learn about requirements that data class should fulfill and their standard functionalities.

Data class is a basic class that is used to hold data/state and contains standard usefulness. A data catchphrase is used to declare a class as a data class.

There may arise a circumstance where you need to create a class exclusively to hold data. In such cases, you can check the class as data to create a data class. For instance,

data class Person(val name: String, var age: Int)

For this class, the compiler consequently produces:

copy() function, equivalents() and hashCode() pair, and toString() type of the essential constructor

componentN() functions

Prior to discussing these highlights in detail, let’s talk about requirements that a data class must fulfill.

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Kotlin Data Class Requirements

Here are the prerequisites:

• The essential constructor should have at least one parameter.
• The parameters of the essential constructor should be set apart as either val (read-just) or var (read-write).
• The class can’t be open, abstract, inner, or sealed.
• The class may extend different classes or carry out interfaces. On the off chance that you are using the Kotlin variant before 1.1, the class can just implement interfaces.

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Example: Kotlin Data Class

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

fun main(args: Array<String>) {
    val salman = User("salman", 29)
    println("name = ${salman.name}")
    println("age = ${salman.age}")
}

At the point when you run the program, the output will be:

name = salman
age = 29

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At the point when you pronounce a data class, the compiler automatically creates a few functions like toString(), equals(), hashcode() and so on in the background. This assists with keeping you code compact. Had you used Java, you would have to write a ton of standard code.

Let’s use these functions:

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Copying

For a data class, you can create a copy of an object with a portion of its properties distinctive using copy() work. Here’s the way it works:

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

fun main(args: Array<String>) {
    val u1 = User("Sohail", 29)
   
    // using copy function to create an object
    val u2 = u1.copy(name = "Haroon")

    println("u1: name = ${u1.name}, name = ${u1.age}")
    println("u2: name = ${u2.name}, name = ${u2.age}")
}

At the point when you run the program, the output will be:

u1: name = Sohail, name = 29
u2: name = Haroon, name = 29

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toString() method

The toString() function returns a string representation of the object.

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

fun main(args: Array<String>) {
    val u1 = User("Sohail", 29)
    println(u1.toString())
}

At the point when you run the program, the output will be:

User(name=Sohail, age=29)

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hashCode() and equivalents()

The hasCode() strategy returns hash code for the object. On the off chance that two objects are equivalent, hashCode() produces a similar integer outcome. Suggested Reading: hashCode()

The equivalents() returns true if two objects are equivalent (has same hashCode()). In the event that items are not equivalent, equals() returns false. Suggested Reading: equals()

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

fun main(args: Array<String>) {
    val u1 = User("Sohail", 29)
    val u2 = u1.copy()
    val u3 = u1.copy(name = "muskan")

    println("u1 hashcode = ${u1.hashCode()}")
    println("u2 hashcode = ${u2.hashCode()}")
    println("u3 hashcode = ${u3.hashCode()}")

    if (u1.equals(u2) == true)
        println("u1 is equal to u2.")
    else
        println("u1 is not equal to u2.")

    if (u1.equals(u3) == true)
        println("u1 is equal to u3.")
    else
        println("u1 is not equal to u3.")
}

At the point when you run the program, the output will be:

u1 hashcode = 71750738
u2 hashcode = 71750738
u3 hashcode = 771732263
u1 is equal to u2.
u1 is not equal to u3.

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Destructuring Declarations

You can destructure an object into various variables using destructuring declaration. For instance:

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

fun main(args: Array<String>) {
    val u1 = User("Sohail", 29, "Male")

    val (name, age, gender) = u1
    println("name = $name")
    println("age = $age")
    println("gender = $gender")
}

At the point when you run the program, the output will be:

name = Sohail
age = 29
gender = Male

This was conceivable on the grounds that the compiler creates componentN() works all properties for a data class. For instance:

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

fun main(args: Array<String>) {
    val u1 = User("Sohail", 29, "Male")

    println(u1.component1())     // Sohail
    println(u1.component2())     // 29  
    println(u1.component3())     // "Male"
}

At the point when you run the program, the output will be:

Sohail
29
Male

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Kotlin OOP