Read from STDIN in Groovy

Reading from the Standard Input, normally the keyboard, is also quite easy.

System.in represents the Standard Input channel.

def defines a variable name. There is no need to declare the type of the variable.

println only takes one argument, so instead of passing a list of values we use the + operator to concatenate the values.

examples/groovy/input_from_stdin.groovy

print "What is your name? "
def name = System.in.newReader().readLine()
println "Your name is " + name

Read from Console in Groovy

A shorter alternative is to use the Console object, but rumors say that it might not work inside an IDE. It works when running in the terminal.

examples/groovy/input_from_console.groovy

def name = System.console().readLine 'What is your name? '
println "Your name is " + name

Converting string to Integer

When we read a value from the standard input it arrives as a string. It cannot be used in numerical operations even if the input looks like a number. In order to use it as a number we have to tell Groovy to treat it as a number. For example as an Integer. That's what "as Integer" is for in the next example:

Rectangular

See the rectangular exercise.

examples/groovy/rectangular.groovy

print "First number: "
def x = System.in.newReader().readLine() as Integer
print "Second number: "
def y = System.in.newReader().readLine() as Integer
println x * y