Convert java to scala code

Question

Converting java to scala code I face a strange Problem An example can be found here https://gist.github.com/geoHeil/895260a04d3673b9848b345edf388a2d The error is

[error] src/main/scala/myOrg/CustomInputMapperWKT.scala:17: overriding method call in trait FlatMapFunction of type (x$1: String)java.util.Iterator[Any];
[error]  method call has incompatible type
[error]   override def call(line: String): Iterator[_] = {

When trying to convert spark java to spark scala API I am struggling to port this java class https://github.com/DataSystemsLab/GeoSpark/blob/master/src/main/java/org/datasyslab/geospark/showcase/UserSuppliedPolygonMapper.java#L59-L81 to scala.

Where

class CustomInputMapperWKT extends FlatMapFunction[String, Any] {
....
override def call(line: String): Iterator[_] = {
val result: collection.Seq[Polygon] with Growable[Polygon] = mutable.Buffer[Polygon]()
result.iterator
  }
}

is the minimal sample describing the problem.

edit

Trying to fix a possible typing problem I substituted Any with its respective type of polygon. But that doesn't help to Fox the problem.

Alex Karpov · Accepted Answer · 2018-09-23 09:32:30Z

2

Have you tried this signature?

override def call(t: String): java.util.Iterator[Any] = {
...

Because this code example is compiled successfully:

import org.apache.spark.api.java.function.FlatMapFunction
import collection.JavaConverters._

class CustomInputMapperWKT extends FlatMapFunction[String, Any] {
  override def call(t: String): java.util.Iterator[Any] = {
    ...
    result.iterator.asJava
  }
}

edited Sep 23, 2018 at 9:32

answered Mar 8, 2017 at 9:10

Alex Karpov

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5 Comments

Georg Heiler Over a year ago

This is partly on the right track. the new Problem now is that val result: collection.Seq[Polygon] with Growable[Polygon] = mutable.Buffer[Polygon]() when called as result.iterator will not produce a java.util.iterator but rather

type mismatch; [error]  found   : Iterator[com.vividsolutions.jts.geom.Polygon] [error]  required: java.util.Iterator[com.vividsolutions.jts.geom.Polygon]

Alex Karpov Over a year ago

can you use JavaConverters as I did? docs.scala-lang.org/overviews/collections/…

Georg Heiler Over a year ago

When using val javaList: java.util.List[Polygon] = scala.collection.JavaConversions.seqAsJavaList(result) javaList.iterator() it will compile but that is not clean scala code. Do you see an alternative? Strangely the implicit mapper will not work.

Alex Karpov Over a year ago

if return of result.iterator.asJava doesn't work, it will be hard to say right now

Georg Heiler Over a year ago

looks like that. strange.

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