Packages

•  package root

  This is the documentation for the Scala standard library.

  This is the documentation for the Scala standard library.

  Package structure

  The scala package contains core types like Int, Float, Array or Option which are accessible in all Scala compilation units without explicit qualification or imports.

  Notable packages include:

  • scala.collection and its sub-packages contain Scala's collections framework
    • scala.collection.immutable - Immutable, sequential data-structures such as Vector, List, Range, HashMap or HashSet
    • scala.collection.mutable - Mutable, sequential data-structures such as ArrayBuffer, StringBuilder, HashMap or HashSet
    • scala.collection.concurrent - Mutable, concurrent data-structures such as TrieMap
  • scala.concurrent - Primitives for concurrent programming such as Futures and Promises
  • scala.io - Input and output operations
  • scala.math - Basic math functions and additional numeric types like BigInt and BigDecimal
  • scala.sys - Interaction with other processes and the operating system
  • scala.util.matching - Regular expressions

  Other packages exist. See the complete list on the right.

  Additional parts of the standard library are shipped as separate libraries. These include:

  • scala.reflect - Scala's reflection API (scala-reflect.jar)
  • scala.xml - XML parsing, manipulation, and serialization (scala-xml.jar)
  • scala.collection.parallel - Parallel collections (scala-parallel-collections.jar)
  • scala.util.parsing - Parser combinators (scala-parser-combinators.jar)
  • scala.swing - A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)

  Automatic imports

  Identifiers in the scala package and the scala.Predef object are always in scope by default.

  Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example, List is an alias for scala.collection.immutable.List.

  Other aliases refer to classes provided by the underlying platform. For example, on the JVM, String is an alias for java.lang.String.

  Definition Classes

  root

•  package scala

  Core Scala types.

  Core Scala types. They are always available without an explicit import.

  Definition Classes

  root

•  package util

  Definition Classes

  scala

•  package control

  Definition Classes

  util

•  object Exception

  Classes representing the components of exception handling.

  Classes representing the components of exception handling.

  Each class is independently composable.

  This class differs from scala.util.Try in that it focuses on composing exception handlers rather than composing behavior. All behavior should be composed first and fed to a Catch object using one of the opt, either or withTry methods. Taken together the classes provide a DSL for composing catch and finally behaviors.

  Examples

  Create a Catch which handles specified exceptions.

  import scala.util.control.Exception._
  import java.net._
  
  val s = "https://www.scala-lang.org/"
  
  // Some(https://www.scala-lang.org/)
  val x1: Option[URL] = catching(classOf[MalformedURLException]) opt new URL(s)
  
  // Right(https://www.scala-lang.org/)
  val x2: Either[Throwable,URL] =
    catching(classOf[MalformedURLException], classOf[NullPointerException]) either new URL(s)
  
  // Success(https://www.scala-lang.org/)
  val x3: Try[URL] = catching(classOf[MalformedURLException], classOf[NullPointerException]) withTry new URL(s)
  
  val defaultUrl = new URL("http://example.com")
  //  URL(http://example.com) because htt/xx throws MalformedURLException
  val x4: URL = failAsValue(classOf[MalformedURLException])(defaultUrl)(new URL("htt/xx"))

  Create a Catch which logs exceptions using handling and by.

  def log(t: Throwable): Unit = t.printStackTrace
  
  val withThrowableLogging: Catch[Unit] = handling(classOf[MalformedURLException]) by (log)
  
  def printUrl(url: String) : Unit = {
    val con = new URL(url) openConnection()
    val source = scala.io.Source.fromInputStream(con.getInputStream())
    source.getLines().foreach(println)
  }
  
  val badUrl = "htt/xx"
  // Prints stacktrace,
  //   java.net.MalformedURLException: no protocol: htt/xx
  //     at java.net.URL.<init>(URL.java:586)
  withThrowableLogging { printUrl(badUrl) }
  
  val goodUrl = "https://www.scala-lang.org/"
  // Prints page content,
  //   <!DOCTYPE html>
  //   <html>
  withThrowableLogging { printUrl(goodUrl) }

  Use unwrapping to create a Catch that unwraps exceptions before rethrowing.

  class AppException(cause: Throwable) extends RuntimeException(cause)
  
  val unwrappingCatch: Catch[Nothing] = unwrapping(classOf[AppException])
  
  def calcResult: Int = throw new AppException(new NullPointerException)
  
  // Throws NPE not AppException,
  //   java.lang.NullPointerException
  //     at .calcResult(<console>:17)
  val result = unwrappingCatch(calcResult)

  Use failAsValue to provide a default when a specified exception is caught.

  val inputDefaulting: Catch[Int] = failAsValue(classOf[NumberFormatException])(0)
  val candidatePick = "seven" // scala.io.StdIn.readLine()
  
  // Int = 0
  val pick = inputDefaulting(candidatePick.toInt)

  Compose multiple Catchs with or to build a Catch that provides default values varied by exception.

  val formatDefaulting: Catch[Int] = failAsValue(classOf[NumberFormatException])(0)
  val nullDefaulting: Catch[Int] = failAsValue(classOf[NullPointerException])(-1)
  val otherDefaulting: Catch[Int] = nonFatalCatch withApply(_ => -100)
  
  val combinedDefaulting: Catch[Int] = formatDefaulting or nullDefaulting or otherDefaulting
  
  def p(s: String): Int = s.length * s.toInt
  
  // Int = 0
  combinedDefaulting(p("tenty-nine"))
  
  // Int = -1
  combinedDefaulting(p(null: String))
  
  // Int = -100
  combinedDefaulting(throw new IllegalStateException)
  
  // Int = 22
  combinedDefaulting(p("11"))

  Definition Classes

  control

• By
• Catch
• Described
• Finally

scala.util.control.Exception

Catch