error

Fixing the Scala error: java.lang.NoSuchMethodError: scala.Product.$init$

As a note to self, when you see a Scala error message that looks like this:

java.lang.NoSuchMethodError: scala.Product.$init$(Lscala/Product;)V

it probably means that you have a mismatch in the Scala versions you’re using in your project. For instance, I just tried to use a library I compiled with Scala 2.12 with Spark, which was compiled with Scala 2.11, and I got that error message. In this case I was able to resolve the problem by recompiling my library with Scala 2.11.

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) )

MacOS/Java AppBundler error: NoSuchFileException: Info.plist

If you’re using the Oracle AppBundler to build a Mac/MacOS application bundle from a Java application and run into this error when running Ant:

NoSuchFileException: <directory path here> Info.plist

I have found that the problem is that I have not set and exported JAVA_HOME. To set and export JAVA_HOME on MacOS 10.12, I use this command in the shell script I use to build my Mac/Java app:

An example of Android StrictMode output (with improper database access)

I was just working with an example of how to use Android’s new Room Persistence Library, and the example I was working with ran some of its code on the main Android thread, also known as its “UI thread.” I knew this was bad, but I wanted to start with someone’s example, and then figure out a good way to get the Room method calls to run on a background thread, such as using an AsyncTask. (The Android docs don’t specify a “best practice” for this atm.)

How to resolve SBT problems by generating a stack trace

This is an excerpt from the Scala Cookbook (partially modified for the internet). This is Recipe 18.12, “Resolving Problems by Getting an SBT Stack Trace.”

Problem

In a Scala project, you’re trying to use SBT to compile, run, or package a project, and it’s failing, and you need to be able to see the stack trace to understand why it’s failing.