在scala中将JSONObject.KeySet（）添加到可变集

Question

I am new to scala. I am working with some JSON objects and would like to get a set of all the keys available in the JSON Objects. I am trying to do something like this:

var set = scala.collection.mutable.Set[String]()
for(condition) {    
  set ++= jsonObject.keySet().asInstanceOf[Set[String]]
}

when I run the code, I get the following error:

java.lang.ClassCastException: java.util.HashMap$KeySet cannot be cast to scala.collection.mutable.Set

The error speaks for itself. I also tried writing the keys to a file:

json2.keySet().toArray().foreach { x => keysWriter.write(x) }

The IDE gives an error saying: overloaded method value write with alternatives: (x$1: Int)Unit <and> (x$1: String)Unit <and> (x$1: Array[Char])Unit cannot be applied to (Object)

So, what would be a better approach to get an accessible list of keys ?

Any help would be appreciated. Thank you.

Answer 1

You could use JavaConverters :

import scala.collection.JavaConverters._

val keys = jsonObject.keySet.asScala

keys is a scala.collection.mutable.Set . To create an immutable Scala Set , do this instead:

val keys = jsonObject.keySet.asScala.toSet