Kotlin in a Nutshell

Kotlin is a modern, programming language that runs on the Java Virtual Machine (JVM).

It’s designed to be fully interoperable with Java while improving upon its verbosity and complexity.

Think “Typescript-JavaScript” relationship… In a way

Biggest thing you will notice is a much leaner syntax..

1. Hello, World!

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

This is the most basic Kotlin program. The main function is the entry point, and println outputs text to the console.

2. Variables and Constants

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val name = "Kotlin"
var age = 10
age += 1

val declares a read-only variable (constant), while var allows modification.

3. Functions

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

Kotlin functions are concise and support string interpolation with $name.

4. Null Safety

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var nullableString: String? = null
nullableString?.let { println(it.length) }

Using ? prevents NullPointerException by enabling safe access.

5. Conditional Expressions

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val number = 10
val result = if (number > 0) "Positive" else "Negative"

if in Kotlin is an expression that returns a value.

6. Loops

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

Kotlin supports range-based loops with ...

7. When Expression

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val grade = "A"
val message = when (grade) {
    "A" -> "Excellent!"
    "B" -> "Good job!"
    else -> "Keep trying!"
}

when replaces switch statements with a more expressive syntax.

8. Classes and Objects

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class Person(val name: String, var age: Int)

val person = Person("Alice", 25)
println(person.name)

Kotlin simplifies class definitions with primary constructors.

9. Extension Functions

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fun String.shout() = this.uppercase()
println("hello".shout())

You can add new functions to existing classes without modifying them.

10. Coroutines

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import kotlinx.coroutines.*

fun main() = runBlocking {
    launch {
        delay(1000L)
        println("Coroutine Example")
    }
    println("Start")
}

Coroutines provide a lightweight way to handle asynchronous operations.

Key Ideas Table

Key Idea	Summary
Kotlin Overview	Kotlin is a modern and expressive language for JVM, Android, and more
Hello World	A simple program to print text to the console
Variables	`val` for constants, `var` for mutable variables
Functions	Kotlin functions are concise and support string interpolation
Null Safety	Prevents `NullPointerException` with safe calls and the Elvis operator
Conditionals	`if` expressions return values, `when` replaces `switch` statements
Loops	Kotlin supports range-based loops
Classes	Kotlin simplifies class definitions with primary constructors
Extension Functions	Add functions to existing classes without modifying them
Coroutines	Lightweight threading with structured concurrency