List

Scala List is immutable sequence of objects that contains the same type of objects, while in java List can be mutable. List are designed to enable functional style of Scala.

val oneTwoThree = List(1, 2, 3) // Creating and initialised List

oneTwoThree(2) //returns the element at index 2(zero based), while is equal to oneTwoThree.apply(2)

Common operations on List are ::: to concatenate lists and :: (cons operator) to insert an element at starting, these operations will always result in new List, as List are immutable objects in Scala.

Scala use:+to append operation, but this rarely used, as the time to append a new element increases with the size of list while prepending (::) always take constant time.

List() or Nil used to create empty List.

Set

var jetSet = Set("Boeing", "Airbus") //Create and initilize Immutable Set with 2 Strings.

jetSet += "Lear" // reassign the jetSet var with a new set containing "Boeing", "Airbus", and "Lear

println(jetSet.contains("Cessna"))

In case of mutable Set

import scala.collection.mutable.Set

val movieSet = Set("Hitch", "Poltergeist") //Create mutable Set

movieSet += "Shrek" // Add Shrek to movieSet

println(movieSet)

Map

Maps are collection of key/value pairs. In Scala, a map is a collection of pairs.In scala Map can be hash table or balanced tree, depending upon the implementation. By default it would be hash table. . A pair is simply a grouping of two values,
not necessarily of the same type, such as ("Alice", 10).You can construct map like :

val scores = Map("Alice" -> 10, "Bob" -> 3, "Cindy" -> 8) OR

val scores = Map(("Alice", 10), ("Bob", 3), ("Cindy", 8))

above is an example of immutable Map[String, Int], whose content can't be change. To make mutable map, please use:

val scores = scala.collection.mutable.Map("Alice" -> 10, "Bob" -> 3, "Cindy" -> 8)

To create blank map :

val scores = new scala.collection.mutable.HashMap[String, Int]

You can access values from Map as :

scores("Bob") // =3 , Like scores.get("Bob") in Java, it will throw exception if value for the requested key not present in Map. you can use

val bobsScore = if (scores.contains("Bob")) scores("Bob") else 0 Or

val bobsScore = scores.getOrElse("Bob", 0)

you can add/update value in map using () :

scores("Bob") = 5 //if Bob present, it will update value for Bob, otherwise add new pair.

you can also use += or -= to add deleted pairs from Map.

To iterate Map :

for ((k, v) <- map)

To visit only keys you can use scores.keySet or to iterate values for (v <- scores.values)

To get an immutable tree map instead of a hash map, use

val scores = scala.collection.immutable.SortedMap("Alice" -> 10, "Fred" -> 7, "Bob" -> 3, "Cindy" -> 8)

To map Java map into Scala you can use conversion utility by importing

import scala.collection.JavaConversions.mapAsScalaMap. To use scala map into java you can use

import scala.collection.JavaConversions.mapAsJavaMap