Scala Initialize List: List.newBuilder, List.empty

Initialize Lists with operators and constructors. Use List.empty and newBuilder.

Initialize list. In Scala lists are immutable. This presents a problem when creating lists. We sometimes need complicated initialization logic.List

Syntax. List.newBuilder can be used to add many values into a temporary collection and then convert that to a list. We can initialize lists by combining 2 lists or adding elements.

Builder example. Here we create a list with the List constructor syntax (a list literal). Then we use List.newBuilder to create the same list with a Builder.

Tip: We need to specify the type of elements as part of the List.newBuilder function call. Here I use Int.

And: We can add elements to the Builder's internal buffer by using the addition operator. With result() we get the final immutable list.

Scala program that uses List.newBuilder // Create a list with values. val numbers = List(10, 11, 12) println(numbers) // Create a list with a Builder. val builder = List.newBuilder[Int] builder += 10 builder += 11 builder += 12 val numbers3 = builder.result() println(numbers3) Output List(10, 11, 12) List(10, 11, 12)

Combine two lists. Sometimes the easiest way to initialize a list is to combine two (or more than two) lists that already exist. Here we create two small lists and then merge them.

Scala program that combines two lists // Add two lists together. val numbers1 = List(13, 14) val numbers2 = List(15, 16) val numbers3 = numbers1 ::: numbers2 println(numbers3) Output List(13, 14, 15, 16)

New element. Here we create a list by taking an existing list and adding another element to its start. This changes the head of the list. This only works with individual elements.

Warning: If we use "::" with another list, that entire list (not its individual elements) will be placed in the head of the new list.

Scala program that initializes list with new element // Initialize a list by placing an element at its start. val numbers1 = List(100, 200) val numbers2 = 50 :: numbers1 println(numbers2) Output List(50, 100, 200)

List.empty. This can be used to initialize lists. We can place new elements alongside List.empty and initialize a new list. We must specify the type of elements (like String).String

Scala program that uses List.empty // Initialize an empty list and add an element to it. val numbers1 = List.empty[String] val numbers2 = "cat" :: numbers1 println(numbers2) Output List(cat)

A summary. Lists are immutable in Scala, so initializing lists is critical. With List.newBuilder and List.empty we can begin initializing lists with ease.

The Dev Codes

.Net

.NET Array Dictionary List String 2D Async DataTable Dates DateTime Enum File For Foreach Format IEnumerable If IndexOf Lambda LINQ Parse Path Process Property Regex Replace Sort Split Static StringBuilder Substring Switch Tuple

Java

Core Array ArrayList HashMap String 2D Cast Character Console Deque Duplicates File For Format HashSet If IndexOf Lambda Math ParseInt Process Random Regex Replace Sort Split StringBuilder Substring Switch Vector While

TheDeveloperBlog.com

Scala Initialize List: List.newBuilder, List.empty

Related Links:

.Net

Java

Related Links