KotlinHow-ToBeginner · 3 min read

How to Create Class in Kotlin: Syntax and Examples

In Kotlin, you create a class using the class keyword followed by the class name and curly braces. Inside the braces, you can define properties and functions to describe the class behavior.

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Syntax

To create a class in Kotlin, use the class keyword, then the class name, and curly braces to hold properties and functions.

class: keyword to declare a class
ClassName: the name of your class (start with uppercase letter)
{ }: braces to contain class body

kotlin

class ClassName {
    // properties and functions go here
}

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Example

This example shows a simple Person class with a property and a function. It creates an object and prints a greeting.

kotlin

class Person(val name: String) {
    fun greet() {
        println("Hello, my name is $name")
    }
}

fun main() {
    val person = Person("Alice")
    person.greet()
}

Output

Hello, my name is Alice

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Common Pitfalls

Common mistakes include forgetting the class keyword, missing parentheses for the constructor, or not using val or var for properties in the primary constructor.

Also, avoid naming classes with lowercase letters, as Kotlin convention uses uppercase for class names.

kotlin

/* Wrong: missing class keyword */
// Person(val name: String) { }

/* Wrong: missing val/var in constructor */
class Person(name: String) { }

/* Right: correct class declaration */
class Person(val name: String) { }

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Quick Reference

Concept	Description	Example
class keyword	Declares a class	class MyClass { }
Primary constructor	Defines properties in class header	class Person(val name: String) { }
Property	Variable inside class	val age: Int = 30
Function	Behavior inside class	fun greet() { println("Hi") }

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Key Takeaways

Use the class keyword followed by the class name and braces to create a class.

Define properties in the primary constructor using val or var inside parentheses after the class name.

Add functions inside the class body to describe behaviors.

Follow Kotlin naming conventions: class names start with uppercase letters.

Always include val or var for constructor parameters to make them properties.