Iterating over Java collections in Scala

Brian_Heylin_16744 0
Viewed 86437

I'm writing some Scala code which uses the Apache POI API. I would like to iterate over the rows contained in the java.util.Iterator that I get from the Sheet class. I would like to use the iterator in a for each style loop, so I have been trying to convert it to a native Scala collection but will no luck.

I have looked at the Scala wrapper classes/traits, but I can not see how to use them correctly. How do I iterate over a Java collection in Scala without using the verbose while(hasNext()) getNext() style of loop?

Here's the code I wrote based on the correct answer:

class IteratorWrapper[A](iter:java.util.Iterator[A])
{
    def foreach(f: A => Unit): Unit = {
        while(iter.hasNext){
          f(iter.next)
        }
    }
}

object SpreadsheetParser extends Application
{
    implicit def iteratorToWrapper[T](iter:java.util.Iterator[T]):IteratorWrapper[T] = new IteratorWrapper[T](iter)

    override def main(args:Array[String]):Unit =
    {
        val ios = new FileInputStream("assets/data.xls")
        val workbook = new HSSFWorkbook(ios)
        var sheet = workbook.getSheetAt(0)
        var rows = sheet.rowIterator()

        for (val row <- rows){
            println(row)
        }
    }
}
scala-java-interop scala collections java
9 Answers

There is a wrapper class (scala.collection.jcl.MutableIterator.Wrapper). So if you define 

implicit def javaIteratorToScalaIterator[A](it : java.util.Iterator[A]) = new Wrapper(it)

then it will act as a sub class of the Scala iterator so you can do foreach.

Admin1

The correct answer here is to define an implicit conversion from Java's Iterator to some custom type. This type should implement a foreach method which delegates to the underlying Iterator. This will allow you to use a Scala for-loop with any Java Iterator.

Daniel_Spiewak_98150

You could convert the Java collection to an array and use that:

val array = java.util.Arrays.asList("one","two","three").toArray
array.foreach(println)

Or go on and convert the array to a Scala list:

val list = List.fromArray(array)
Fabian_Steeg_181540
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