object Console extends AnsiColor
Implements functionality for printing Scala values on the terminal. For reading values use StdIn. Also defines constants for marking up text on ANSI terminals.
Console Output
Use the print methods to output text.
scala> Console.printf( "Today the outside temperature is a balmy %.1f°C. %<.1f°C beats the previous record of %.1f°C.\n", -137.0, -135.05) Today the outside temperature is a balmy -137.0°C. -137.0°C beats the previous record of -135.1°C.
ANSI escape codes
Use the ANSI escape codes for colorizing console output either to STDOUT or STDERR.
import Console.{GREEN, RED, RESET, YELLOW_B, UNDERLINED} object PrimeTest { def isPrime(): Unit = { val candidate = io.StdIn.readInt().ensuring(_ > 1) val prime = (2 to candidate - 1).forall(candidate % _ != 0) if (prime) Console.println(s"${RESET}${GREEN}yes${RESET}") else Console.err.println(s"${RESET}${YELLOW_B}${RED}${UNDERLINED}NO!${RESET}") } def main(args: Array[String]): Unit = isPrime() }
$ scala PrimeTest |
1234567891 |
yes |
$ scala PrimeTest |
56474 |
NO! |
IO redefinition
Use IO redefinition to temporarily swap in a different set of input and/or output streams. In this example the stream based method above is wrapped into a function.
import java.io.{ByteArrayOutputStream, StringReader} object FunctionalPrimeTest { def isPrime(candidate: Int): Boolean = { val input = new StringReader(s"$candidate\n") val outCapture = new ByteArrayOutputStream val errCapture = new ByteArrayOutputStream Console.withIn(input) { Console.withOut(outCapture) { Console.withErr(errCapture) { PrimeTest.isPrime() } } } if (outCapture.toByteArray.nonEmpty) // "yes" true else if (errCapture.toByteArray.nonEmpty) // "NO!" false else throw new IllegalArgumentException(candidate.toString) } def main(args: Array[String]): Unit = { val primes = (2 to 50) filter (isPrime) println(s"First primes: $primes") } }
$ scala FunctionalPrimeTest |
First primes: Vector(2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47) |
- Source
- Console.scala
- Grouped
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- AnsiColor
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Value Members
- 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
- final def ##: Int
Equivalent to
x.hashCode
except for boxed numeric types andnull
.Equivalent to
x.hashCode
except for boxed numeric types andnull
. 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. Fornull
returns a hashcode wherenull.hashCode
throws aNullPointerException
.- returns
a hash value consistent with ==
- Definition Classes
- AnyRef → Any
- final def ==(arg0: Any): Boolean
The expression
x == that
is equivalent toif (x eq null) that eq null else x.equals(that)
.The expression
x == that
is equivalent toif (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
- final val BLACK: String("\u001B[30m")
Foreground color for ANSI black
Foreground color for ANSI black
- Definition Classes
- AnsiColor
- final val BLACK_B: String("\u001B[40m")
Background color for ANSI black
Background color for ANSI black
- Definition Classes
- AnsiColor
- final val BLINK: String("\u001B[5m")
ANSI blink
ANSI blink
- Definition Classes
- AnsiColor
- final val BLUE: String("\u001B[34m")
Foreground color for ANSI blue
Foreground color for ANSI blue
- Definition Classes
- AnsiColor
- final val BLUE_B: String("\u001B[44m")
Background color for ANSI blue
Background color for ANSI blue
- Definition Classes
- AnsiColor
- final val BOLD: String("\u001B[1m")
ANSI bold
ANSI bold
- Definition Classes
- AnsiColor
- final val CYAN: String("\u001B[36m")
Foreground color for ANSI cyan
Foreground color for ANSI cyan
- Definition Classes
- AnsiColor
- final val CYAN_B: String("\u001B[46m")
Background color for ANSI cyan
Background color for ANSI cyan
- Definition Classes
- AnsiColor
- final val GREEN: String("\u001B[32m")
Foreground color for ANSI green
Foreground color for ANSI green
- Definition Classes
- AnsiColor
- final val GREEN_B: String("\u001B[42m")
Background color for ANSI green
Background color for ANSI green
- Definition Classes
- AnsiColor
- final val INVISIBLE: String("\u001B[8m")
ANSI invisible
ANSI invisible
- Definition Classes
- AnsiColor
- final val MAGENTA: String("\u001B[35m")
Foreground color for ANSI magenta
Foreground color for ANSI magenta
- Definition Classes
- AnsiColor
- final val MAGENTA_B: String("\u001B[45m")
Background color for ANSI magenta
Background color for ANSI magenta
- Definition Classes
- AnsiColor
- final val RED: String("\u001B[31m")
Foreground color for ANSI red
Foreground color for ANSI red
- Definition Classes
- AnsiColor
- final val RED_B: String("\u001B[41m")
Background color for ANSI red
Background color for ANSI red
- Definition Classes
- AnsiColor
- final val RESET: String("\u001B[0m")
Reset ANSI styles
Reset ANSI styles
- Definition Classes
- AnsiColor
- final val REVERSED: String("\u001B[7m")
ANSI reversed
ANSI reversed
- Definition Classes
- AnsiColor
- final val UNDERLINED: String("\u001B[4m")
ANSI underlines
ANSI underlines
- Definition Classes
- AnsiColor
- final val WHITE: String("\u001B[37m")
Foreground color for ANSI white
Foreground color for ANSI white
- Definition Classes
- AnsiColor
- final val WHITE_B: String("\u001B[47m")
Background color for ANSI white
Background color for ANSI white
- Definition Classes
- AnsiColor
- final val YELLOW: String("\u001B[33m")
Foreground color for ANSI yellow
Foreground color for ANSI yellow
- Definition Classes
- AnsiColor
- final val YELLOW_B: String("\u001B[43m")
Background color for ANSI yellow
Background color for ANSI yellow
- Definition Classes
- AnsiColor
- final def asInstanceOf[T0]: T0
Forces the compiler to treat the receiver object as having type
T0
, even though doing so may violate type safety.Forces the compiler to treat the receiver object as having type
T0
, even though doing so may violate type safety.This method is useful when you believe you have type information the compiler doesn't, and it also isn't possible to check the type at runtime. In such situations, skipping type safety is the only option.
It is platform dependent whether
asInstanceOf
has any effect at runtime. It might do a runtime type test on the erasure ofT0
, insert a conversion (such as boxing/unboxing), fill in a default value, or do nothing at all.In particular,
asInstanceOf
is not a type test. It does **not** mean:this match { case x: T0 => x case _ => throw ClassCastException("...")
Use pattern matching or isInstanceOf for type testing instead.
Situations where
asInstanceOf
is useful:- when flow analysis fails to deduce
T0
automatically - when down-casting a type parameter or an abstract type member (which cannot be checked at runtime due to type erasure) If there is any doubt and you are able to type test instead, you should do so.
Be careful of using
asInstanceOf
whenT0
is a primitive type. WhenT0
is primitive,asInstanceOf
may insert a conversion instead of a type test. If your intent is to convert, use atoT
method (x.toChar
,x.toByte
, etc.).- returns
the receiver object.
- Definition Classes
- Any
- Exceptions thrown
ClassCastException
if the receiver is not an instance of the erasure ofT0
, if that can be checked on this platform
- when flow analysis fails to deduce
- 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.
- 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 ofAnyRef
, and has three additional properties:- It is consistent: for any non-null instances
x
andy
of typeAnyRef
, multiple invocations ofx.eq(y)
consistently returnstrue
or consistently returnsfalse
. - For any non-null instance
x
of typeAnyRef
,x.eq(null)
andnull.eq(x)
returnsfalse
. null.eq(null)
returnstrue
.
When overriding the
equals
orhashCode
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
- It is consistent: for any non-null instances
- def equals(arg0: AnyRef): Boolean
The equality method for reference types.
- def err: PrintStream
The default error, can be overridden by
withErr
- 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 betweenfinalize
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
- def flush(): Unit
Flushes the output stream.
Flushes the output stream. This function is required when partial output (i.e. output not terminated by a newline character) has to be made visible on the terminal.
- final def getClass(): Class[_ <: AnyRef]
Returns the runtime class representation of the object.
- def hashCode(): Int
The hashCode method for reference types.
- def in: BufferedReader
The default input, can be overridden by
withIn
- final def isInstanceOf[T0]: Boolean
Test whether the dynamic type of the receiver object has the same erasure as
T0
.Test whether the dynamic type of the receiver object has the same erasure as
T0
.Depending on what
T0
is, the test is done in one of the below ways:T0
is a non-parameterized class type, e.g.BigDecimal
: this method returnstrue
if the value of the receiver object is aBigDecimal
or a subtype ofBigDecimal
.T0
is a parameterized class type, e.g.List[Int]
: this method returnstrue
if the value of the receiver object is someList[X]
for anyX
. For example,List(1, 2, 3).isInstanceOf[List[String]]
will return true.T0
is some singleton typex.type
or literalx
: this method returnsthis.eq(x)
. For example,x.isInstanceOf[1]
is equivalent tox.eq(1)
T0
is an intersectionX with Y
orX & Y: this method is equivalent to
x.isInstanceOf[X] && x.isInstanceOf[Y]T0
is a unionX | Y
: this method is equivalent tox.isInstanceOf[X] || x.isInstanceOf[Y]
T0
is a type parameter or an abstract type member: this method is equivalent toisInstanceOf[U]
whereU
isT0
's upper bound,Any
ifT0
is unbounded. For example,x.isInstanceOf[A]
whereA
is an unbounded type parameter will return true for any value ofx
.
This is exactly equivalent to the type pattern
_: T0
- returns
true
if the receiver object is an instance of erasure of typeT0
;false
otherwise.
- Definition Classes
- Any
- Note
due to the unexpectedness of
List(1, 2, 3).isInstanceOf[List[String]]
returning true andx.isInstanceOf[A]
whereA
is a type parameter or abstract member returning true, these forms issue a warning.
- 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
- 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
- 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
- def out: PrintStream
The default output, can be overridden by
withOut
- def print(obj: Any): Unit
Prints an object to
out
using itstoString
method.Prints an object to
out
using itstoString
method.- obj
the object to print; may be null.
- def printf(text: String, args: Any*): Unit
Prints its arguments as a formatted string to the default output, based on a string pattern (in a fashion similar to printf in C).
Prints its arguments as a formatted string to the default output, based on a string pattern (in a fashion similar to printf in C).
The interpretation of the formatting patterns is described in java.util.Formatter.
- text
the pattern for formatting the arguments.
- args
the arguments used to instantiating the pattern.
- Exceptions thrown
java.lang.IllegalArgumentException
if there was a problem with the format string or arguments
- def println(x: Any): Unit
Prints out an object to the default output, followed by a newline character.
Prints out an object to the default output, followed by a newline character.
- x
the object to print.
- def println(): Unit
Prints a newline character on the default output.
- def setErrDirect(err: PrintStream): Unit
- Attributes
- protected
- def setInDirect(in: BufferedReader): Unit
- Attributes
- protected
- def setOutDirect(out: PrintStream): Unit
- Attributes
- protected
- final def synchronized[T0](arg0: => T0): T0
Executes the code in
body
with an exclusive lock onthis
.Executes the code in
body
with an exclusive lock onthis
.- returns
the result of
body
- Definition Classes
- AnyRef
- 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
- AnyRef → Any
- final def wait(): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait--.
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException])
- Note
not specified by SLS as a member of AnyRef
- final def wait(arg0: Long, arg1: Int): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-int-
- Definition Classes
- AnyRef
- Annotations
- @throws(classOf[java.lang.InterruptedException])
- Note
not specified by SLS as a member of AnyRef
- final def wait(arg0: Long): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-.
- def withErr[T](err: OutputStream)(thunk: => T): T
Sets the default error stream for the duration of execution of one thunk.
Sets the default error stream for the duration of execution of one thunk.
- err
the new error stream.
- thunk
the code to execute with the new error stream active
- returns
the results of
thunk
- See also
withErr[T](err:PrintStream)(thunk: => T)
- def withErr[T](err: PrintStream)(thunk: => T): T
Set the default error stream for the duration of execution of one thunk.
Set the default error stream for the duration of execution of one thunk.
- err
the new error stream.
- thunk
the code to execute with the new error stream active
- returns
the results of
thunk
withErr(Console.out) { err.println("This goes to default _out_") }
- See also
withErr[T](err:OutputStream)(thunk: => T)
Example: - def withIn[T](in: InputStream)(thunk: => T): T
Sets the default input stream for the duration of execution of one thunk.
Sets the default input stream for the duration of execution of one thunk.
- in
the new input stream.
- thunk
the code to execute with the new input stream active
- returns
the results of
thunk
- See also
withIn[T](reader:Reader)(thunk: => T)
- def withIn[T](reader: Reader)(thunk: => T): T
Sets the default input stream for the duration of execution of one thunk.
Sets the default input stream for the duration of execution of one thunk.
- thunk
the code to execute with the new input stream active
- returns
the results of
thunk
val someFile:Reader = openFile("file.txt") withIn(someFile) { // Reads a line from file.txt instead of default input println(readLine) }
- See also
withIn[T](in:InputStream)(thunk: => T)
Example: - def withOut[T](out: OutputStream)(thunk: => T): T
Sets the default output stream for the duration of execution of one thunk.
Sets the default output stream for the duration of execution of one thunk.
- out
the new output stream.
- thunk
the code to execute with the new output stream active
- returns
the results of
thunk
- See also
withOut[T](out:PrintStream)(thunk: => T)
- def withOut[T](out: PrintStream)(thunk: => T): T
Sets the default output stream for the duration of execution of one thunk.
Sets the default output stream for the duration of execution of one thunk.
- out
the new output stream.
- thunk
the code to execute with the new output stream active
- returns
the results of
thunk
withOut(Console.err) { println("This goes to default _error_") }
- See also
withOut[T](out:OutputStream)(thunk: => T)
Example:
Console Output
These methods provide output via the console.
IO Defaults
These values provide direct access to the standard IO channels
IO Redefinition
These methods allow substituting alternative streams for the duration of a body of code. Threadsafe by virtue of scala.util.DynamicVariable.
This is the documentation for the Scala standard library.
Package structure
The scala package contains core types like
Int
,Float
,Array
orOption
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 frameworkscala.collection.immutable
- Immutable, sequential data-structures such asVector
,List
,Range
,HashMap
orHashSet
scala.collection.mutable
- Mutable, sequential data-structures such asArrayBuffer
,StringBuilder
,HashMap
orHashSet
scala.collection.concurrent
- Mutable, concurrent data-structures such asTrieMap
scala.concurrent
- Primitives for concurrent programming such asFutures
andPromises
scala.io
- Input and output operationsscala.math
- Basic math functions and additional numeric types likeBigInt
andBigDecimal
scala.sys
- Interaction with other processes and the operating systemscala.util.matching
- Regular expressionsOther 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 forscala.collection.immutable.List
.Other aliases refer to classes provided by the underlying platform. For example, on the JVM,
String
is an alias forjava.lang.String
.