Question

I use a Java method that returns an object or null if a value was not found. So I need to check for null values:

val value = javaobject.findThing(xyz)
if(value != null) {
    value.doAnotherThing()
} else {
    warn("Value not found.")
}

Can I write this code shorter with the Box concept? I have read the Lift-Wiki-documentation about the Box concept, but I don’t understand how to use it with Java null values.

Answer 1

@TimN is right, you could use Box(value) to create a Box from a possibly null value, but you’ll get a deprecation warning.

scala> val v: Thing = null
v: Thing = null

scala> Box[Thing](v)
<console>:25: warning: method apply in trait BoxTrait is deprecated: Use legacyNullTest
              Box[Thing](v)

While you could use Box.legacyNullTest, if this is what you’re doing, then I would just stick with the standard library and use Option.

Option(javaobject.findThing(xyz)) match {
    case Some(thing) => thing.doAnotherThing()
    case _ => warn("Value not found.")
}

And if you needed a Box to pass around, Option will automagically convert to a Box:

scala> val b: Box[Thing] = Option(v)
b: net.liftweb.common.Box[Thing] = Empty