Using Scala in Java - how to convert a Java Object to Option<Object>

Question

I'm writing in java, and I need to use external library that is written in scala. In particular, I need the following constructor:

new PartitionMetadata(partitionId: Int, leader: Option[Broker], replicas: Seq[Broker], isr: Seq[Broker] = collection.this.Seq.empty[Nothing], errorCode: Short = kafka.common.ErrorMapping.NoError)

I was able to convert all but the leader : Option[Broker] and the Seq parameters in my java code:

partitionMetadata = new kafka.api.PartitionMetadata(
  partitionId, leader.getBroker(),(Seq)brokerReplicas, (Seq)brokerIsr, errorCode);

I'm getting the following error in my editor:

'PartitionMetadata(int, scala.Option<kafka.cluster.Broker>, scala.collection.Seq<kafka.cluster.Broker>, scala.collection.Seq<kafka.cluster.Broker>, short)' in 'kafka.api.PartitionMetadata'
cannot be applied to (int, kafka.cluster.Broker, scala.collection.Seq, scala.collection.Seq, short)

Is it possible to use a Scala constructor in Java? Also, how do I convert a Java Object (leader) to a Option?

Lastly, am I converting the ArrayList -> Scala.collection.Seq fields correctly?

Thanks

Sohan Jain · Accepted Answer · 2015-08-11 18:43:41Z

4

Yes, it's possible to use this scala constructor in Java. The error message from your editor gives you a hint: it expects a scala.Option<kafka.cluster.Broker> as the second argument.

You can create that scala.Option as follows: scala.Option.apply(leader.getBroker())

Also, you shouldn't just cast your java array lists to scala.Seq. Instead, check out scala.collection.JavaConversions

answered Aug 11, 2015 at 18:43

Sohan Jain

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2 Comments

pl0u Over a year ago

thanks for the answer! From the conversion, it looks like there is no way to convert any type into scala.collection.Seq Is there another method for conversion that I use instead? Is there a way to create an empty scala.collection.Seq in Java, then subsequently populate it with my elements?

Sohan Jain Over a year ago

You can use asScalaBuffer. Check out its method header: it takes in a java.util.List (which an ArrayList satisfies), and returns a scala.collection.mutable.Buffer (which extends Seq)

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