string format in Scala

Question

New to Scala and see people are using sign f ahead of a string, here is an example I tried which works. Wondering what is the function of sign f ? Does it need to be combined to use with %s? Tried to search some tutorials but failed. Thanks.

object HelloWorld {

   def main(args: Array[String]) {
      var start = "Monday";
      var end = "Friday";
      var palindrome = "Dot saw I was Tod";
      println(f"date >= $start%s and date <= $end%s" + palindrome);
      // output date >= Monday and date <= FridayDot saw I was Tod
   }
}

Answer 1

http://docs.scala-lang.org/overviews/core/string-interpolation.html

The f Interpolator

Prepending f to any string literal allows the creation of simple formatted strings, similar to printf in other languages. When using the f interpolator, all variable references should be followed by a printf-style format string, like %d.

PS. another somewhat related feature is http://docs.scala-lang.org/overviews/quasiquotes/expression-details

Answer 2

See the explanation here . For people coming from C the f interpolator is a printf style formatter. % is to denote the type of data and with a $ you may may refer to a previously defined variable. The % in not mandatory. Its just that you will get a format that is decided by the compiler at compile time. Bit uyou may want to change the output format sometimes.

So if i take an example ,

var start = "Monday";
  var end = "Friday";
  val age = 33
  var palindrome = "Dot saw I was Tod";
  println(f"date >= $start and date <= $end and age<= $age%f" + palindrome);

I could omit the %f and i will see a output of 33 as it will inferred as Int. However i could use %f if i wanted to format it as a float. Also if you use a incompatible formatted you will receive a error at compile time.