Why is mkString not working in Scala?

Question

I can't get an array to print like a string normally in Scala

  val a = Array("woot","yeah","ok then").sorted

  for (i <- a.length-1 to 0 by -1)
    println(s"$i: ${a(i)}")

  val ab = ArrayBuffer(for (e <- a if e != null) yield e*3)

  println(ab.mkString(" "))

For some reason, this prints:

2: yeah
1: woot
0: ok then
ArrayBuffer([Ljava.lang.String;@5034c75a)

And I was expecting it to print "yeahyeahyeah wootwootwoot ok thenok thenok then" , that is, the items in the array (as strings) separated by a space. Why isn't it working and what am I doing wrong?

EDIT: ok, it was showing that because I was initializing ab to be a one-element ArrayBuffer with that array as the element instead of the elements of that inner array being separate elements of the array buffer.

Answer 1

If you want to print each element of the array, concatenated three times, with spaces between the entries, then it's just:

println((for (e <- a) yield e * 3).mkString(" "))

it gives:

ok thenok thenok then wootwootwoot yeahyeahyeah

(and this is the right order, because you wanted it sorted alphabetically, and o < w < y )

If you want to reverse the array before printing, you can initialize it to

val a = Array("woot","yeah","ok then").sorted.reverse

Answer 2

我想你的意思是

val ab = ArrayBuffer((for (e <- a if e != null) yield e*3): _*)

Answer 3

Some shorter answer using more functional approach:

val a = Array("woot","yeah","ok then").sorted.reverse
a.map(_ * 3).map(elem => print(elem + " ")

Edit: If you want to have a result in some new variable you can do that:

val string = a.map(_ * 3).mkString(" ")