1. Introduction

In this tutorial, we aim to understand and differentiate between data classes and sealed classes in Kotlin. You will learn about the different purposes they serve, and when to use each one in your programming tasks.

By the end of this tutorial, you'll know:
- What data classes and sealed classes are in Kotlin
- The differences and similarities between them
- Practical use cases for each

No specific prerequisites are required for this tutorial. However, basic knowledge of Kotlin syntax and object-oriented programming would be beneficial.

2. Step-by-Step Guide

Kotlin Data Classes

A data class in Kotlin is a concise way to define a class that is used to hold data. The data keyword is used to define a data class.

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

In a data class, hashCode(), equals(), toString(), copy(), and componentN() functions are automatically generated.

Kotlin Sealed Classes

Sealed classes are used to represent restricted class hierarchies. They allow you to represent a fixed number of known subclasses. The sealed keyword is used to define a sealed class.

sealed class Expr
data class Const(val number: Double) : Expr()
data class Sum(val e1: Expr, val e2: Expr) : Expr()
object NotANumber : Expr()

In a sealed class, subclasses are declared in the same file as the sealed class itself. This allows you to know all possible subclasses.

3. Code Examples

Example 1: Data Class

data class Book(val name: String, val author: String)

fun main() {
    val book1 = Book("Kotlin for Beginners", "John Doe")
    println(book1)
    // Output: Book(name=Kotlin for Beginners, author=John Doe)
}

In this example, a data class Book is created with two properties: name and author. The toString() method is automatically generated and used in the println() function.

Example 2: Sealed Class

sealed class Operation {
    data class Add(val value: Int) : Operation()
    data class Subtract(val value: Int) : Operation()
    object Multiply : Operation()
    object Divide : Operation()
}

fun execute(op: Operation, int1: Int, int2: Int): Int = when (op) {
    is Operation.Add -> int1 + int2
    is Operation.Subtract -> int1 - int2
    is Operation.Multiply -> int1 * int2
    is Operation.Divide -> int1 / int2
}

In this example, a sealed class Operation is created with four subclasses. The when expression is used with the sealed class instance to execute different operations.

4. Summary

In this tutorial, we learned that data classes in Kotlin are primarily used to hold data, and they automatically generate utility functions. On the other hand, sealed classes define a limited class hierarchy, allowing us to model our domain with precision.

The next step could be exploring more about other Kotlin classes like enum classes and abstract classes. For additional resources, consider reading the official Kotlin documentation or the book "Kotlin in Action" by Svetlana Isakova and Dmitry Jemerov.

5. Practice Exercises

1. Create a data class Person with properties name and age. Create a few instances of Person and use the copy() function.
2. Create a sealed class Shape with subclasses Circle, Square, and Rectangle. Write functions to calculate the area of each shape.

Remember, practice is the key to mastering any concept. Keep experimenting with different use cases and scenarios. Happy coding!