Java iterators in Scala

Question

I have some java code I am trying to convert to scala:

package hello;

class HelloWorldApp {
    public static void main(String[] args) {
            public SortedMap<Long, Long> toDates = new TreeMap<>();

            Iterator<Long> iterLong = toDates.keySet().iterator();
            while( iterLong.hasNext() )
            {
                System.out.println("TEST");
            }

    }
}

I used a converter to get this:

package hello

//remove if not needed
import scala.collection.JavaConversions._

object HelloWorldApp {

  def main(args: Array[String]): Unit = {
    val toDates: SortedMap[Long, Long] = new TreeMap[Long, Long]()
    val iterLong: Iterator[Long] = toDates.keySet.iterator()
    while (iterLong.hasNext) println("TEST")
  }

}

The problem is the iterator() call really is not liked in scala (which I am executing through spark)

<console>:190: error: type mismatch;
 found   : java.util.Iterator[Long]
 required: scala.collection.Iterator[Long]
                         val iterLong: Iterator[Long] = toDates.keySet.iterator()

I understand what he error is saying basically. Though, I am not sure how to force the type of scala.collection on the keySet.iterator() call.

I did do this:

    val iterLong: scala.collection.Iterator[Long] = toDates.keySet.iterator()

To no avail What else can I add to have that iterator come back and work correclty in the loop?

Recommended way is to import JavaConverters._ and call .asScala when needed. See here — insan-e
– insan-e, Commented Oct 11, 2017 at 22:30

HTNW · Accepted Answer · 2017-10-11 22:39:58Z

3

You can either convert from Java to Scala, or you can just work with the Java one directly.

Converting

Add this import

import collection.JavaConverters._

and then use the new asJava/asScala methods to convert collections:

val iterLong: Iterator[Long] = (...).toScala

Directly Using Java Types

When doing interop with java collections, it’s common to do

import java.{ util => ju }

So that Java collection types can be accesed via ju.??? without fear of naming conflicts. With the above import in scope, write

val iterLong: ju.Iterator[Long] = ... // or let type inference do it for you

and use the Java API

answered Oct 11, 2017 at 22:39

HTNW

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