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:

    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.swing - A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)
    • scala.util.parsing - Parser combinators (scala-parser-combinators.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 = "http://www.scala-lang.org/"

// Some(http://www.scala-lang.org/)
val x1: Option[URL] = catching(classOf[MalformedURLException]) opt new URL(s)

// Right(http://www.scala-lang.org/)
val x2: Either[Throwable,URL] =
  catching(classOf[MalformedURLException], classOf[NullPointerException]) either new URL(s)

// Success(http://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 = "http://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

class Catch[+T] extends Described

A container class for catch/finally logic.

Pass a different value for rethrow if you want to probably unwisely allow catching control exceptions and other throwables which the rest of the world may expect to get through.

T

result type of bodies used in try and catch blocks

Source
Exception.scala
Linear Supertypes
Described, AnyRef, Any
Ordering
  1. Alphabetic
  2. By Inheritance
Inherited
  1. Catch
  2. Described
  3. AnyRef
  4. Any
Implicitly
  1. by any2stringadd
  2. by StringFormat
  3. by Ensuring
  4. by ArrowAssoc
  1. Hide All
  2. Show All
Visibility
  1. Public
  2. All

Instance Constructors

  1. new Catch(pf: Catcher[T], fin: Option[Finally] = None, rethrow: (Throwable) ⇒ Boolean = shouldRethrow)

    pf

    Partial function used when applying catch logic to determine result value

    fin

    Finally logic which if defined will be invoked after catch logic

    rethrow

    Predicate on throwables determining when to rethrow a caught Throwable

Value Members

  1. final def !=(arg0: Any): Boolean

    Test two objects for inequality.

    Test two objects for inequality.

    returns

    true if !(this == that), false otherwise.

    Definition Classes
    AnyRef → Any
  2. final def ##(): Int

    Equivalent to x.hashCode except for boxed numeric types and null.

    Equivalent to x.hashCode except for boxed numeric types and null. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For null returns a hashcode where null.hashCode throws a NullPointerException.

    returns

    a hash value consistent with ==

    Definition Classes
    AnyRef → Any
  3. def +(other: String): String
    Implicit
    This member is added by an implicit conversion from Catch[T] to any2stringadd[Catch[T]] performed by method any2stringadd in scala.Predef.
    Definition Classes
    any2stringadd
  4. def ->[B](y: B): (Catch[T], B)
    Implicit
    This member is added by an implicit conversion from Catch[T] to ArrowAssoc[Catch[T]] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc
    Annotations
    @inline()
  5. final def ==(arg0: Any): Boolean

    The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

    The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

    returns

    true if the receiver object is equivalent to the argument; false otherwise.

    Definition Classes
    AnyRef → Any
  6. def andFinally(body: ⇒ Unit): Catch[T]

    Create a new Catch container from this object and the supplied finally body.

    Create a new Catch container from this object and the supplied finally body.

    body

    The additional logic to apply after all existing finally bodies

  7. def apply[U >: T](body: ⇒ U): U

    Apply this catch logic to the supplied body.

  8. final def asInstanceOf[T0]: T0

    Cast the receiver object to be of type T0.

    Cast the receiver object to be of type T0.

    Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.

    returns

    the receiver object.

    Definition Classes
    Any
    Exceptions thrown

    ClassCastException if the receiver object is not an instance of the erasure of type T0.

  9. def clone(): AnyRef

    Create a copy of the receiver object.

    Create a copy of the receiver object.

    The default implementation of the clone method is platform dependent.

    returns

    a copy of the receiver object.

    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( ... ) @native()
    Note

    not specified by SLS as a member of AnyRef

  10. def desc: String
    Definition Classes
    Described
  11. def either[U >: T](body: ⇒ U): Either[Throwable, U]

    Apply this catch logic to the supplied body, mapping the result into Either[Throwable, T] - Left(exception) if an exception was caught, Right(T) otherwise.

  12. def ensuring(cond: (Catch[T]) ⇒ Boolean, msg: ⇒ Any): Catch[T]
    Implicit
    This member is added by an implicit conversion from Catch[T] to Ensuring[Catch[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  13. def ensuring(cond: (Catch[T]) ⇒ Boolean): Catch[T]
    Implicit
    This member is added by an implicit conversion from Catch[T] to Ensuring[Catch[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  14. def ensuring(cond: Boolean, msg: ⇒ Any): Catch[T]
    Implicit
    This member is added by an implicit conversion from Catch[T] to Ensuring[Catch[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  15. def ensuring(cond: Boolean): Catch[T]
    Implicit
    This member is added by an implicit conversion from Catch[T] to Ensuring[Catch[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  16. final def eq(arg0: AnyRef): Boolean

    Tests whether the argument (that) is a reference to the receiver object (this).

    Tests whether the argument (that) is a reference to the receiver object (this).

    The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:

    • It is consistent: for any non-null instances x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.
    • For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false.
    • null.eq(null) returns true.

    When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).

    returns

    true if the argument is a reference to the receiver object; false otherwise.

    Definition Classes
    AnyRef
  17. def equals(arg0: Any): Boolean

    The equality method for reference types.

    The equality method for reference types. Default implementation delegates to eq.

    See also equals in scala.Any.

    returns

    true if the receiver object is equivalent to the argument; false otherwise.

    Definition Classes
    AnyRef → Any
  18. val fin: Option[Finally]
  19. def finalize(): Unit

    Called by the garbage collector on the receiver object when there are no more references to the object.

    Called by the garbage collector on the receiver object when there are no more references to the object.

    The details of when and if the finalize method is invoked, as well as the interaction between finalize and non-local returns and exceptions, are all platform dependent.

    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( classOf[java.lang.Throwable] )
    Note

    not specified by SLS as a member of AnyRef

  20. def formatted(fmtstr: String): String

    Returns string formatted according to given format string.

    Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).

    Implicit
    This member is added by an implicit conversion from Catch[T] to StringFormat[Catch[T]] performed by method StringFormat in scala.Predef.
    Definition Classes
    StringFormat
    Annotations
    @inline()
  21. final def getClass(): Class[_]

    Returns the runtime class representation of the object.

    Returns the runtime class representation of the object.

    returns

    a class object corresponding to the runtime type of the receiver.

    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  22. def hashCode(): Int

    The hashCode method for reference types.

    The hashCode method for reference types. See hashCode in scala.Any.

    returns

    the hash code value for this object.

    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  23. final def isInstanceOf[T0]: Boolean

    Test whether the dynamic type of the receiver object is T0.

    Test whether the dynamic type of the receiver object is T0.

    Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression 1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.

    returns

    true if the receiver object is an instance of erasure of type T0; false otherwise.

    Definition Classes
    Any
  24. val name: String
    Attributes
    protected
    Definition Classes
    Catch → Described
  25. final def ne(arg0: AnyRef): Boolean

    Equivalent to !(this eq that).

    Equivalent to !(this eq that).

    returns

    true if the argument is not a reference to the receiver object; false otherwise.

    Definition Classes
    AnyRef
  26. final def notify(): Unit

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Definition Classes
    AnyRef
    Annotations
    @native()
    Note

    not specified by SLS as a member of AnyRef

  27. final def notifyAll(): Unit

    Wakes up all threads that are waiting on the receiver object's monitor.

    Wakes up all threads that are waiting on the receiver object's monitor.

    Definition Classes
    AnyRef
    Annotations
    @native()
    Note

    not specified by SLS as a member of AnyRef

  28. def opt[U >: T](body: ⇒ U): Option[U]

    Apply this catch logic to the supplied body, mapping the result into Option[T] - None if any exception was caught, Some(T) otherwise.

  29. def or[U >: T](other: Catch[U]): Catch[U]
  30. def or[U >: T](pf2: Catcher[U]): Catch[U]

    Create a new Catch with additional exception handling logic.

  31. val pf: Catcher[T]
  32. val rethrow: (Throwable) ⇒ Boolean
  33. final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
    AnyRef
  34. def toEither: Catch[Either[Throwable, T]]
  35. def toOption: Catch[Option[T]]

    Convenience methods.

  36. def toString(): String

    Creates a String representation of this object.

    Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.

    returns

    a String representation of the object.

    Definition Classes
    Described → AnyRef → Any
  37. def toTry: Catch[Try[T]]
  38. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  39. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  40. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... ) @native()
  41. def withApply[U](f: (Throwable) ⇒ U): Catch[U]

    Create a Catch object with the same isDefinedAt logic as this one, but with the supplied apply method replacing the current one.

  42. def withDesc(s: String): Catch.this.type
    Definition Classes
    Described
  43. def withTry[U >: T](body: ⇒ U): Try[U]

    Apply this catch logic to the supplied body, mapping the result into Try[T] - Failure if an exception was caught, Success(T) otherwise.

  44. def →[B](y: B): (Catch[T], B)
    Implicit
    This member is added by an implicit conversion from Catch[T] to ArrowAssoc[Catch[T]] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc

Inherited from Described

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion any2stringadd from Catch[T] to any2stringadd[Catch[T]]

Inherited by implicit conversion StringFormat from Catch[T] to StringFormat[Catch[T]]

Inherited by implicit conversion Ensuring from Catch[T] to Ensuring[Catch[T]]

Inherited by implicit conversion ArrowAssoc from Catch[T] to ArrowAssoc[Catch[T]]

Ungrouped