Console
scala.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)
Attributes
- Source:
- Console.scala
- Graph
- Supertypes
- Self type
- Console.type