Scala Cheat Sheet

@main def hello(): Unit =
  println("Hello, World!")

// Single line comment

/* Multi-line
   comment */

val name = "Scala"
println(s"Hello, $name!")  // Hello, Scala!

import scala.io.StdIn
val input = StdIn.readLine("Enter: ")
println(s"You entered: $input")

val name = "John"

var count = 0

val age: Int = 25

val nums = List(1, 2, 3)

val ages = Map("John" -> 30, "Jane" -> 25)

val pair = (1, "hello")

val name: Option[String] = Some("John")

5 + 3    // 8 (addition)
5 - 3    // 2 (subtraction)
5 * 3    // 15 (multiplication)
5 / 3    // 1 (integer division)
5 % 3    // 2 (modulus)

5 == 3   // false (equal)
5 != 3   // true (not equal)
5 > 3    // true (greater)
5 < 3    // false (less)
5 >= 3   // true (greater or equal)
5 <= 3   // false (less or equal)

true && false  // false (AND)
true || false  // true (OR)
!true          // false (NOT)

var x = 5
x += 3   // x = 8
x -= 2   // x = 6
x *= 2   // x = 12
x /= 3   // x = 4

"Hello" + " World"  // concatenation
"abc" * 3           // "abcabcabc"

for (i <- 1 to 5) {
  println(i)  // 1, 2, 3, 4, 5
}

for (i <- 0 until 5) {
  println(i)  // 0, 1, 2, 3, 4
}

val fruits = List("apple", "banana")
for (fruit <- fruits) {
  println(fruit)
}

val doubled = for (n <- nums) yield n * 2

var i = 0
while (i < 5) {
  println(i)
  i += 1
}

nums.foreach(n => println(n))
nums.foreach(println)  // shorthand

for (i <- 1 to 10 if i % 2 == 0) {
  println(i)  // 2, 4, 6, 8, 10
}

val max = if (a > b) a else b

x match {
  case 1 => "one"
  case 2 | 3 => "two or three"
  case _ => "other"
}

def greet(name: String): String = {
  s"Hello, $name!"
}

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

def greet(name: String = "World") = s"Hello, $name!"

val add = (a: Int, b: Int) => a + b

def add(a: Int)(b: Int) = a + b

nums.map(_ * 2)

nums.filter(_ > 0)

nums.flatMap(n => List(n, n * 2))

nums.reduce(_ + _)

nums.foldLeft(0)(_ + _)

people.groupBy(_.city)

class Dog(val name: String) {
  def bark(): String = s"$name says woof!"
}

case class Person(name: String, age: Int)

object Singleton {
  def doSomething(): Unit = {}
}

trait Greetable {
  def greet(): String
}

class Person extends Animal with Greetable

person match {
  case Person(name, age) => s"$name is $age"
  case _ => "unknown"
}

opt match {
  case Some(value) => value
  case None => "default"
}

x match {
  case n if n > 0 => "positive"
  case _ => "non-positive"
}