Collections in Scala

• Declaring an array usese type Array.

val nums = new Array[Int](10)

All entries are initialized to 0 in above example.

• Int array is directly mapped to primitive int[] in Java.

• Creating array with initial values

val names = new Array("David", "Ben")

• Use paranthesis to access the entries instead of square braces like in Java.

E.g.:    nums(0) = 22 or val n = nums(2)

• Looping throught the elements or looping using indices.

E.g.:
for(element <- nums)

for(i <- 0 until nums.length)

Note: 0 to nums.length includes nums.length whereas 0 until nums.length excludes nums.length

• ArrayBuffer class in Scala is equivalent of ArrayList in Java. However it's mutable, take extra care while using it.

Some examples of creation, append or +, appendAll or ++

val b = new ArrayBuffer[Int]()
b.append(10)
b += 22
b.append(20, 30)

// appending more than one element, type gets inferred
b += (21, 22)

// appending ArrayBuffer to another ArrayBuffer using appendAll method
b.appendAll(ArrayBuffer[Int](11, 12, 14))

// appending ArrayBuffer to another ArrayBuffer using ++ operator
b ++= ArrayBuffer[Int](100, 200)    

// appending array to ArrayBuffer
b ++= Array(101, 201)    

for(i <- b) print(i + ", ")

• Use toArray and toBuffer methods to go back and forth between Array and ArrayBuffer objects.

• Array can be printed using make string - mkString method

Array(1, 2, 3).mkString(", ")
            // prints String = 1 , 2 , 3

Array(1, 2, 3).mkString("[", ", ", "]")
            // prints String = [1, 2, 3]

• Map by default is immutable. Mutable map declaration requires explicite specifying of package.

val scores = Map("Van" -> 5, "Sha" -> 4)val mscores = scala.collection.mutable.Map("Van" -> 5, "Sha" -> 4)

Adding and removing entries:
mscores -= "Sha"
mscores += ("Vin" -> 7)