Future Basics
A Future is a promise of an answer that will arrive later, like ordering food and getting a buzzer. Meanwhile the program keeps doing other things.
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Syntax
import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global
val future = Future {
// asynchronous computation
result
}
future.map(x => expression)Future Basics
A Future[T] represents a value that will become available asynchronously, running its computation on a separate thread managed by an implicit ExecutionContext.
Awaiting a Future's result synchronously (blocking until it completes) requires Await.result(future, timeout), generally reserved for simple scripts, tests, or a program's final step rather than everyday async code. Both scala.concurrent.Await and an ExecutionContext (commonly ExecutionContext.global) must be imported to run and block on a Future this way.
Note:
Blocking with Await.result is mainly appropriate for scripts, tests, or a program's very last step -- production async code usually chains callbacks instead.
Example: Future Basics
import scala.concurrent.{Future, Await}
import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.duration._
object Main extends App {
val future: Future[Int] = Future {
Thread.sleep(50)
21 * 2
}
val result = Await.result(future, 5.seconds)
println(s"Future result: $result")
}Login to try C/C++/Java/PHP code in the editor
Related Topics
{# common_mistakes/chapter_summary/browser_support: on Hindi pages the
view already swaps in the hi_ translation fields (or blanks these
out if untranslated), so this renders correctly for both languages
without a lang_code check here. #}
Common Mistakes
- Forgetting the
ExecutionContextimport, so it fails withCannot find an implicit ExecutionContext. - Calling
Await.resulteverywhere, which blocks the thread and defeats the purpose of aFuture. - Letting the program end before the
Futurefinishes, so its output never appears.
Chapter Summary
- Implicit parameters and type classes provide flexible behavior.
- Generics and variance describe how types relate.
lazy val,LazyList, andFuturesupport delayed computation and asynchronous work.
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