📌 Data Classes in Kotlin

In Kotlin, a data class is a special type of class used to store data. It automatically provides useful functions like equals(), hashCode(), toString(), and copy() without needing to write boilerplate code.

✅ 1. Defining a Data Class

• Use the data keyword before the class declaration.

• Must have at least one primary constructor parameter.

• Commonly used for data models or DTOs (Data Transfer Objects).

📌 Syntax:

kotlin
data class User(val name: String, var age: Int)fun () {    val user1 = User("Alice", 25)    val user2 = User("Bob", 30)    println(user1) // Output: User(name=Alice, age=25)    println(user2) // Output: User(name=Bob, age=30)}

✅ 2. Features of Data Classes

Data classes in Kotlin provide the following built-in functions:

🔎 a. toString()

• Provides a readable string representation of the object.

kotlin
println(user1.toString()) // Output: User(name=Alice, age=25)

🔎 b. equals() and hashCode()

• Automatically compares object properties instead of references.

kotlin
val user3 = User("Alice", 25)println(user1 == user3) // Output: true

• hashCode() generates a unique code based on property values.

🔎 c. copy()

• Creates a copy of the object, with the option to modify specific properties.

kotlin
val user4 = user1.copy(age = 26)println(user4) // Output: User(name=Alice, age=26)

✅ 3. Data Class with Functions

You can also add functions to a data class.

kotlin
data class Product(val name: String, var price: Double) {    fun () {        println("Product: $name, Price: $fun () {    val product = Product("Laptop", 1200.0)    product.displayInfo()}

Output:

yaml
Product: Laptop, Price: $1200.0

✅ 4. Component Functions with Data Classes

Data classes provide component functions (component1(), component2(), etc.) to access properties. This is useful for destructuring.

📌 Example: Destructuring Declaration

kotlin
val (name, age) = User("Charlie", 28)println("Name: $name, Age: Name: Charlie, Age: 28

✅ 5. Data Class with Default Values

You can provide default values to constructor parameters.

kotlin
data class Employee(val name: String = "Unknown", val salary: Double = 30000.0)fun main() {    val emp1 = Employee()    val emp2 = Employee("John", 45000.0)    println(emp1) // Output: Employee(name=Unknown, salary=30000.0)    println(emp2) // Output: Employee(name=John, salary=45000.0)}

✅ 6. Limitations of Data Classes

• Data classes cannot be abstract, open, sealed, or inner.

• Data classes must have at least one parameter in the primary constructor.

✅ Conclusion

• Data Classes are ideal for storing and representing data.

• They provide built-in functionality like toString(), equals(), copy(), and hashCode().

• Use destructuring declarations for easy property access.

• Ideal for use in API responses, database entities, or DTOs.