Kotlin Essentials - Modern Programming for Android and Beyond

📚 Table of Contents

• 1. Introduction to Kotlin
• 2. Setting Up the Environment
• 3. Basic Syntax
• 4. Variables and Data Types
• 5. Functions
• 6. Conditionals and Loops
• 7. Lists, Sets, and Maps
• 8. Classes and Objects
• 9. Null Safety
• 10. Lambdas & Higher-Order Functions
• 11. Coroutines (Async Programming)
• 12. Best Practices
• 13. Mini Project
• 14. Conclusion

1. Introduction to Kotlin

Kotlin is a modern, concise, and powerful programming language developed by JetBrains. It runs on the JVM and is fully interoperable with Java. It’s widely used for Android development, backend, and even multiplatform apps.

• Official language for Android development.
• Interoperable with Java.
• Null-safe and concise syntax.

Tip: Kotlin is easier to read and write than Java — perfect for beginners!

2. Setting Up the Environment

You can run Kotlin code in multiple ways:

• Using Kotlin Playground (online).
• Installing IntelliJ IDEA (official IDE).
• Using the Kotlin CLI compiler.

fun main() {
    println("Hello, Kotlin!")
}

3. Basic Syntax

Every Kotlin program starts with a main function:

fun main() {
    println("Welcome to Kotlin!")
}

Note: Kotlin uses println() for printing text.

4. Variables and Data Types

Kotlin uses val for constants and var for mutable variables.

val name = "Alice"     // Immutable
var age = 25           // Mutable
val pi: Double = 3.14  // Explicit type

Common data types include Int, Double, Boolean, String, and Char.

5. Functions

fun greet(name: String): String {
    return "Hello, $name!"
}

fun main() {
    println(greet("Bob"))
}

Tip: Single-expression functions can be written like this:

fun add(a: Int, b: Int) = a + b

6. Conditionals and Loops

val score = 85

if (score >= 90) {
    println("Excellent")
} else if (score >= 70) {
    println("Good")
} else {
    println("Needs Improvement")
}

for (i in 1..5) {
    println(i)
}

7. Lists, Sets, and Maps

val fruits = listOf("Apple", "Banana", "Cherry")
val numbers = mutableListOf(1, 2, 3)
val user = mapOf("name" to "John", "age" to 30)

println(fruits[0])       // Apple
println(user["name"])    // John

8. Classes and Objects

class Person(val name: String, var age: Int) {
    fun introduce() {
        println("Hi, I'm $name and I'm $age years old.")
    }
}

fun main() {
    val person = Person("Alice", 25)
    person.introduce()
}

Note: Kotlin automatically creates getters and setters for properties.

9. Null Safety

Kotlin eliminates null pointer exceptions using nullable types:

var name: String? = null
println(name?.length) // Safe call
println(name ?: "Unknown") // Elvis operator

10. Lambdas & Higher-Order Functions

val numbers = listOf(1, 2, 3, 4, 5)
val doubled = numbers.map { it * 2 }
println(doubled)

Tip: Functions that take other functions as arguments are called higher-order functions.

11. Coroutines (Async Programming)

Coroutines make asynchronous code simple and readable:

import kotlinx.coroutines.*

fun main() = runBlocking {
    launch {
        delay(1000L)
        println("World!")
    }
    println("Hello,")
}

Note: Coroutines are part of kotlinx.coroutines.

12. Best Practices

• Prefer val over var for immutability.
• Use meaningful function and variable names.
• Take advantage of null safety.
• Use Kotlin extensions and data classes.

13. Mini Project: Simple Calculator

fun add(a: Int, b: Int) = a + b
fun subtract(a: Int, b: Int) = a - b
fun multiply(a: Int, b: Int) = a * b
fun divide(a: Int, b: Int) = a / b

fun main() {
    println("Sum: ${add(10, 5)}")
    println("Product: ${multiply(4, 3)}")
}

Challenge: Extend this calculator to accept user input using readLine().

14. Conclusion

Kotlin combines simplicity, power, and safety. It’s a great language for Android, backend, and cross-platform development.

Once you master Kotlin basics, explore advanced features like Coroutines, Generics, and Jetpack Compose.