I have the following code snippet:
val map = new LinkedHashMap[String,String]
map.put("City","Dallas")
println(map.get("City"))
This outputs Some(Dallas) instead of just Dallas. Whats the problem with my code ?
Thank You
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3 Answers
Use the apply method, it returns directly the String and throws a NoSuchElementException if the key is not found:
scala> import scala.collection.mutable.LinkedHashMap
import scala.collection.mutable.LinkedHashMap
scala> val map = new LinkedHashMap[String,String]
map: scala.collection.mutable.LinkedHashMap[String,String] = Map()
scala> map.put("City","Dallas")
res2: Option[String] = None
scala> map("City")
res3: String = Dallas
1 Comment
kassens
apply is a magic method that gets called if you 'call' an object. map("City") is equivalent to map.apply("City").It's not really a problem.
While Java's Map version uses null to indicate that a key don't have an associated value, Scala's Map[A,B].get returns a Options[B], which can be Some[B] or None, and None plays a similar role to java's null.
REPL session showing why this is useful:
scala> map.get("State")
res6: Option[String] = None
scala> map.get("State").getOrElse("Texas")
res7: String = Texas
Or the not recommended but simple get:
scala> map.get("City").get
res8: String = Dallas
scala> map.get("State").get
java.util.NoSuchElementException: None.get
at scala.None$.get(Option.scala:262)
Check the Option documentation for more goodies.
4 Comments
Tom
Thanks for the reply. But how to make it output just the value instead of Some(value) ?
pedrofurla
@Tom I have just add one example of how to use it.
missingfaktor
@Tom: You could just use
map("City").
Kevin Meredith
Related post on better alternative to
map.get().get - stackoverflow.com/questions/19969225/…There are two more ways you can handle Option results.
You can pattern match them:
scala> map.get("City") match {
| case Some(value) => println(value)
| case _ => println("found nothing")
| }
Dallas
Or there is another neat approach that appears somewhere in Programming in Scala. Use foreach to process the result. If a result is of type Some, then it will be used. Otherwise (if it's None), nothing happens:
scala> map.get("City").foreach(println)
Dallas
scala> map.get("Town").foreach(println)
