exception

Scala/Java: How to convert a stack trace to a string for printing with a logger

As a quick note, I just got a little bit better about logging stack traces when writing Java or Scala code. In Scala I used to get the text from a stack trace and then log it like this:

// this works, but it's not too useful/readable
logger.error(exception.getStackTrace.mkString("\n"))

In that code, getStackTrace returns a sequence, which I convert to a String before printing it.

Java: A Java list `tail` function (for ArrayList, LinkedList, etc.)

As a brief note today, I was working on a Java/Android application recently, and I needed a “tail” function when I was working on a Java list. What I mean by that is that Scala has a tail function that returns all elements of the list except for the head element, like this:

scala> val x = List(1,2,3,4)
x: List[Int] = List(1, 2, 3, 4)

scala> x.tail
res1: List[Int] = List(2, 3, 4)  //head element removed

and I wanted the same thing in Java.

Functional error handling in Scala

Because functional programming is like algebra, there are no null values or exceptions. But of course you can still have exceptions when you try to access servers that are down or files that are missing, so what can you do? This lesson demonstrates the techniques of functional error handling in Scala.

The `f` string interpolator does not work with Dotty (Scala 3)

If you happen to be using Dotty (Scala 3) and find that the f string interpolator isn’t working, it’s a known bug. (It was implemented with a macro, and the old, experimental macro system has been dropped.) I’m writing this in January, 2019; I don’t know when it will work again. You can use the Java/Scala String.format method until it’s fixed:

val pi = scala.math.Pi
println( "%1.5f".format(pi) )

Some Scala Exception ‘allCatch’ examples

At the time of this writing there aren’t many examples of the Scala Exception object allCatch method to be found, so I thought I’d share some examples here.

In each example I first show the "success" case, and then show the "failure" case. Other than that, I won’t explain these, but hopefully seeing them in the REPL will be enough to get you pointed in the right direction: