Specific usage of mkString in Scala

Time:2019-10-7

1. Use of mkString () method:

  • The mkString (seq: String) method is to segment the original string using a specific string seq.
  • The mkString (statrt: String, seq: String, end: String) method is to segment the original string using a specific string seq, at the same time, add the string start before the original string, and then add the string end.

object Test {
 def main(args: Array[String]): Unit = {
 var name : String = "Hello LittleLawson"
 var age :Int = 2
 println(name.mkString)
 println(name.mkString(" "))//separate string with space

 var str0 = "scala"
 println(str0.mkString(","))//separate string with comma

 println(str0.mkString("begin",",","end"))

 /*
 1.mkString is used in the inner List,That is say ,Elements in the list is applied.
  */
 val a = List(1,2,3,4)
 val b = new StringBuilder()
 println(a.mkString("List(" , ", " , ")"))

 }
}

The results are as follows:
Hello LittleLawson
H e l l o   L i t t l e L a w s o n
s,c,a,l,a
begins,c,a,l,aend
List(1, 2, 3, 4)

Process finished with exit code 0

2. Scala transforms a collection into a string by mkString method

Problem
If you want to convert a collection element into a string, you may also add separators, prefixes, and suffixes.

Solution
Using the mkString method to print a collection content, here is a simple example:


scala> val a = Array("apple", "banana", "cherry")
a: Array[String] = Array(apple, banana, cherry)

scala> a.mkString
res3: String = applebananacherry

Using the mkString method, you will see that the result is not beautiful. Let’s add a separator:


scala> a.mkString(",")
res4: String = apple,banana,cherry

scala> a.mkString(" ")
res5: String = apple banana cherry

This will look much better. You can also add a prefix and a suffix:


scala> a.mkString("[", ", ", "]")
res6: String = [apple, banana, cherry]

If you want to convert an escape collection into a string, such as a nested array, you first expand the nested array, and then call the mkString method:


scala> val a = Array(Array("a", "b"), Array("c", "d"))
a: Array[Array[String]] = Array(Array(a, b), Array(c, d))

scala> a.flatten.mkString(",")
res7: String = a,b,c,d

Discussion

You can call the toString method of the collection, but it returns the name of the collection with the information of the collection element:


scala> val v = Vector("apple", "banana", "cherry")
v: scala.collection.immutable.Vector[String] = Vector(apple, banana, cherry)

scala> v.toString
res8: String = Vector(apple, banana, cherry)

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