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
- Authors:
-
Matthias Zenger
- Since
-
1.0
- Graph
-
- Supertypes
- Self type
-
Console.type
Members list
Grouped members
Console Output
These methods provide output via the console.
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.
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.
Attributes
Prints an object to out using its toString method.
Prints an object to out using its toString method.
Value parameters
- obj
-
the object to print; may be null.
Attributes
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.
Value parameters
- args
-
the arguments used to instantiating the pattern.
- text
-
the pattern for formatting the arguments.
Attributes
- Throws
-
java.lang.IllegalArgumentException
if there was a problem with the format string or arguments
Prints a newline character on the default output.
Prints a newline character on the default output.
Attributes
IO Defaults
These values provide direct access to the standard IO channels
The default error, can be overridden by withErr
The default error, can be overridden by withErr
Attributes
The default input, can be overridden by withIn
The default input, can be overridden by withIn
Attributes
The default output, can be overridden by withOut
The default output, can be overridden by withOut
Attributes
IO Redefinition
These methods allow substituting alternative streams for the duration of a body of code. Threadsafe by virtue of scala.util.DynamicVariable.
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.
Value parameters
- err
-
the new error stream.
- thunk
-
the code to execute with the new error stream active
Attributes
- Returns
-
the results of
thunk - See also
-
withErr[T](err:OutputStream)(thunk: =>T) - Example
-
withErr(Console.out) { err.println("This goes to default _out_") }
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.
Value parameters
- err
-
the new error stream.
- thunk
-
the code to execute with the new error stream active
Attributes
- Returns
-
the results of
thunk - See also
-
withErr[T](err:PrintStream)(thunk: =>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.
Value parameters
- thunk
-
the code to execute with the new input stream active
Attributes
- 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) }
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.
Value parameters
- in
-
the new input stream.
- thunk
-
the code to execute with the new input stream active
Attributes
- Returns
-
the results of
thunk - See also
-
withIn[T](reader:Reader)(thunk: =>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.
Value parameters
- out
-
the new output stream.
- thunk
-
the code to execute with the new output stream active
Attributes
- Returns
-
the results of
thunk - See also
-
withOut[T](out:OutputStream)(thunk: => T) - Example
-
withOut(Console.err) { println("This goes to default _error_") }
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.
Value parameters
- out
-
the new output stream.
- thunk
-
the code to execute with the new output stream active
Attributes
- Returns
-
the results of
thunk - See also
-
withOut[T](out:PrintStream)(thunk: => T)
color-magenta
Foreground color for ANSI magenta
color-blue
Foreground color for ANSI blue
color-red
Foreground color for ANSI red
color-cyan
Foreground color for ANSI cyan
style-control
Reset ANSI styles
ANSI underlines
color-green
Foreground color for ANSI green
color-yellow
Foreground color for ANSI yellow
color-white
Foreground color for ANSI white