Convert scala list to json using loop

Question

I tried a lot to convert my scala list to Json using while loop; the code is as follows:

 var json = null
 while (list != null) {
   json = new Gson().toJson(list)
 }

the json variable must be accessed outside of the loop, so I declared it outside of the loop and initialized with null, but the Scala compiler gives me a type mismatch exception...

You're initializing json to null, and then trying to assign a String value to it. BTW, you probably want to have json be a val and do a conditional initialization rather than use a var. — Diego Basch
– Diego Basch, Commented Sep 21, 2013 at 5:56

Erik Kaplun · Accepted Answer · 2013-09-21 12:36:28Z

3

Why are you using a while loop to convert a single list to JSON? Until you explain why you need a loop (or, repeated conversions to JSON, more generally speaking), I'd suggest the following trivial snippet:

val json = new Gson().toJson(list)

Note that I've also changed var json to val json.

However, if all you want to know is how to get rid of the type mismatch exception, just change:

var json = null

to

var json: String = null

or

var json: String = _

If you don't declare json to be of type String, Scala will implicitly take it to be (i.e. infer) of type Null, and it's not possible to assign values of type String to a variable of type Null.

edited Sep 21, 2013 at 12:36

answered Sep 21, 2013 at 10:33

Erik Kaplun

38.5k15 gold badges102 silver badges113 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Erik Kaplun Over a year ago

they both most definitely are at least on my computer using Scala 2.10.2.

tuxdna · Accepted Answer · 2013-12-12 19:24:55Z

0

This function works fine for List and Map both using plain Scala constructs:

def toJson(a: Any): String = {
  a match {
    // number
    case m: Number => m.toString
    // string
    case m: String => "\"" + m + "\""
    case m: Map[AnyRef, AnyRef] => {
"{" + (m map { x => val key = x._1; toJson(key) + ": " + toJson(m(key)) } mkString (", ")) + "}"
}

    case l: Seq[AnyRef] => { "[" + (l map (toJson(_)) mkString (",")) + "]" }

    // for anything else: tuple
    case m: Product => toJson(m.productIterator.toList)
    case m: AnyRef => "\"" + m.toString + "\""
  }
}

Complete example is located here: https://gist.github.com/tuxdna/7926531

answered Dec 12, 2013 at 19:24

tuxdna

8,5074 gold badges47 silver badges64 bronze badges

Collectives™ on Stack Overflow

Convert scala list to json using loop

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related