How could I initialize val object in the try catch block?

Question

I have this code in Scala, a object should be value not a variable, How can I initialize the a object in the try block?

object SomeObject {
  private val a : SomeClass

  try {
    a=someThing // this statement may throw an exception
  }
  catch {
    case ex:  Exception=> {
       ex.printStackTrace()
    }
  }
}

Answer 1

Scala tries to avoid undefined/null values. However, you can solve the problem by giving return values for the cases if the try fails and initializing a with the whole try expression:

private val a: SomeClass =
  try {
    someThing // this statement may throw an exception
  } catch {
    case ex: Exception => {
      ex.printStackTrace()
      someDefault
    }
  }

Update: In Scala it would be probably more idiomatic to use Try from scala.util:

val x : Int =
  Try({
    someThing
  }).recoverWith({
    // Just log the exception and keep it as a failure.
    case (ex: Throwable) => ex.printStackTrace; Failure(ex);
  }).getOrElse(1);

Try allows you to compose computations that can fail with an exception in various ways. For example, if you have two computations of type Try you can call

thing1.orElse(thing2).getOrElse(someDefault)

This runs thing1 and returns its result, if it's successful. If it fails, it continues with thing2. If it fails too, returns someDefault. You can also use recover or recoverWith to recover from some exceptions using partial functions (and potentially reuse those partial functions).

Answer 2

Since in Scala blocks have return values, and the last expression is the return value per default, you can do this:

object SomeObject {
  private val a : SomeClass = { //this additional block not necessary, but added for clarity
      try {
        someThing // this statement may throw an exception
      }
      catch {
        case ex:  Exception=> {
           ex.printStackTrace()
           null
        }
      }
    }
} 

. However, I have to add that this looks like you're trying to accomplish something potentially blowing up in your face later - you will need null checks in any code that uses the value.