Fundamentals of Kotlin Programming Language

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Table of Contents

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• Introduction to Kotlin
• Kotlin Basics

• Variables and Data Types
• Control Flow Statements
• Functions in Kotlin

• Object-Oriented Programming in Kotlin

• Classes and Objects
• Inheritance in Kotlin
• Polymorphism in Kotlin

• Kotlin Collections

• Lists in Kotlin
• Sets and Maps in Kotlin

Introduction to Kotlin

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Kotlin is a modern, statically typed programming language developed by JetBrains. It’s designed to be concise, safe, and interoperable with Java code. Kotlin compiles to JVM (Java Virtual Machine) bytecode, making it a great choice for Android app development.

Kotlin Basics

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Variables and Data Types

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In Kotlin, you can declare variables using the val or var keyword. The val keyword is used for immutable variables, while var is used for mutable variables.

// Immutable variable declaration
val name: String = "John Doe"

// Mutable variable declaration
var age: Int = 25

Kotlin has several built-in data types:

Data Type	Description
Int	Whole numbers, e.g., 1, 2, 3, etc.
String	Sequence of characters, e.g., “Hello”, “World”, etc.
Boolean	True or false values
Double	Decimal numbers, e.g., 3.14, -0.5, etc.

Control Flow Statements

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Kotlin has several control flow statements:

• Conditional statements: if, when
• Loops: for, while

// Conditional statement
val x = 10
if (x > 5) {
println("x is greater than 5")
}

// When expression
val color = "Red"
when (color) {
"Red" -> println("The color is red")
"Green" -> println("The color is green")
else -> println("The color is neither red nor green")
}

Functions in Kotlin

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Functions in Kotlin are defined using the fun keyword. You can also use function literals to define functions inline.

// Function definition
fun greet(name: String) {
println("Hello, $name!")
}

// Function literal
val greet = fun(name: String) {
println("Hello, $name!")
}

Object-Oriented Programming in Kotlin

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Classes and Objects

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Classes in Kotlin are defined using the class keyword. You can define constructors, properties, and methods within a class.

// Class definition
class Person(val name: String, val age: Int) {
fun greet() {
println("Hello, my name is $name and I'm $age years old.")
}
}

// Creating an object of the class
val person = Person("John Doe", 25)
person.greet()

Inheritance in Kotlin

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Kotlin supports single inheritance. You can use the : Class syntax to inherit from a parent class.

// Parent class definition
open class Animal {
open fun sound() {
println("The animal makes a sound.")
}
}

// Child class definition
class Dog : Animal() {
override fun sound() {
println("The dog barks.")
}
}

Polymorphism in Kotlin

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Kotlin supports method overriding and method overloading. You can use the override keyword to override methods, and use function parameters to overload methods.

// Method overriding
open class Shape {
open fun area() {
println("The shape has an area.")
}
}

class Circle : Shape() {
override fun area() {
println("The circle has a radius of 5 units and an area of 78.54 square units.")
}
}

Kotlin Collections

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Lists in Kotlin

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Kotlin lists are defined using the List interface.

// List definition
val numbers = listOf(1, 2, 3, 4, 5)
println(numbers.size) // Output: 5

// Accessing elements
val firstNumber = numbers[0]
println(firstNumber) // Output: 1

// Modifying the list
numbers.add(6)
println(numbers.size) // Output: 6

Sets and Maps in Kotlin

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Kotlin sets are defined using the Set interface, while maps are defined using the Map interface.

// Set definition
val numbers = setOf(1, 2, 3, 4, 5)
println(numbers.size) // Output: 5

// Map definition
val map = mapOf("John" to 25, "Alice" to 30)
println(map["John"]) // Output: 25