Console
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
Console Output
These methods provide output via the console.
Prints an object to out using its toString method.
- Value Params
- obj
the object to print; may be null.
- Source
- Console.scala
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.
- Source
- Console.scala
Prints out an object to the default output, followed by a newline character.
- Value Params
- x
the object to print.
- Source
- Console.scala
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.
- Value Params
- args
the arguments used to instantiating the pattern.
- text
the pattern for formatting the arguments.
- Throws
- java.lang.IllegalArgumentException
if there was a problem with the format string or arguments
- Source
- Console.scala
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.
Sets the default output stream for the duration of execution of one thunk.
- Value Params
- 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:OutputStream)(thunk: => T)- Example
withOut(Console.err) { println("This goes to default _error_") }- Source
- Console.scala
Sets the default output stream for the duration of execution of one thunk.
- Value Params
- 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)- Source
- Console.scala
Set the default error stream for the duration of execution of one thunk.
- Value Params
- 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:OutputStream)(thunk: => T)- Example
withErr(Console.out) { err.println("This goes to default _out_") }- Source
- Console.scala
Sets the default error stream for the duration of execution of one thunk.
- Value Params
- 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)- Source
- Console.scala
Sets the default input stream for the duration of execution of one thunk.
- Value Params
- thunk
the code to execute with the new input stream active
- Returns
the results of
thunk- See also
withIn[T](in:InputStream)(thunk: => T)- Example
val someFile:Reader = openFile("file.txt") withIn(someFile) { // Reads a line from file.txt instead of default input println(readLine) }- Source
- Console.scala
Sets the default input stream for the duration of execution of one thunk.
- Value Params
- 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)- Source
- Console.scala