Scala, Java, Unix, MacOS tutorials (page 325)

Scala FAQ: Can you share some examples of the Scala for loop syntax?

Sure. I'm going to start with a comparison to Java for loops, because that's what I was just thinking about.

In Java you might write a for loop with a counter like this:

for (int i = 0; i < 10; i++) {
  System.out.println(i);
}

The equivalent for loop in Scala looks like this:

for (i <- 1 to 10) {
  println(i)
}

(The use of parentheses isn’t necessary in either example, but most for loops will be longer.)

Scala String FAQ: How can I count the number of times (occurrences) a character appears in a String?

Use the count method on the string, using a simple anonymous function, as shown in this example in the REPL:

scala> "hello world".count(_ == 'o')
res0: Int = 2

There are other ways to count the occurrences of a character in a string, but that's very simple and easy to read.

UPDATE: I originally posted this article in January, 2013, and it's now mid-February, 2013, and we're no longer looking for reviewers. I've only kept this page here so people won't get 404 errors.

OLD CONTENT:

Interested in being a reviewer for the Scala Cookbook?

Nothing too earth shattering here today, but if you need an example of the Scala Map class syntax (how to create a Scala Map), or just want to copy and paste a map of month names to numbers (or numbers to names), I hope the following code is helpful:

Summary: How to properly use the Scala Option/Some/None idiom to initialize empty var fields -- and specifically how not to use null values for the same purpose.

When you get started in the Scala world, you quickly learn that null values are a bad thing. Scala makes it easy to replace null values with something better, and that something better is what I call the Option/Some/None pattern (or idiom).

Scala shell script FAQ: How do I create a Unix/Linux shell script to run a small Scala script?

If you want to run a Scala script as a Unix or Linux shell script -- such as hello.sh -- write your script like this:

Scala List FAQ: Can you share some Scala List class examples?

The Scala List class may be the most commonly used data structure in Scala applications. Therefore, it's very helpful to know how create lists, merge lists, select items from lists, operate on each element in a list, and so on.

In this tutorial, I'll share examples of the most common List operations (methods).

Scala List class FAQ: How do I create a List in Scala? (Also asked as, how do I create and initially populate a List in Scala?)

You can create a Scala List in several different ways, including these approaches:

Scala collections FAQ: Can you share an example that shows how to get the max or min value from a collection using the Scala reduceLeft collections method?

I don't have much time today, but sure, here's a quick example. The following code will determine which student has the max (top/high) score:

I've been trying to find some good Scala currency and money libraries lately, and I just ran across the following list of projects on the Joda Money Github project. That URL contains the following list of Java and JVM-based projects that should all be usable in Scala:

Summary: A discussion of Scala type annotations and type ascription.

While Scala normally determines the type you want to use automatically, such as this Int:

scala> val x = 1
x: Int = 1

there may be times you want to control the type, such as if you want a Byte, Short, Long, Double, Float, etc. In these cases you can annotate your type when you create it, like this:

(Note: I don't have any immediate solutions in this article; it's more of a discussion of where I'm at today when looking at handling money/currency in Scala.)

As a quick note, I've started to look at handling money/currency in Scala, and I'm also starting to explore a couple of money/currency libraries.

Scala FAQ: Can you share an example of how to create an implicit class in Scala 2.10?

Sure. As the question implies, the implicit class functionality changed in Scala 2.10, so let's take a look at the new syntax.

Background

Rather than create a separate library of String utility methods, like a StringUtilities class, you want to add your own behavior(s) to the String class, so you can write code like this:

SBT FAQ: How do I set the desired Scala compiler version in the SBT build.sbt configuration file?

Set the value of the scalaVersion variable in your SBT build.sbt file. For instance, to use Scala 2.9.2, put an entry like this in the build.sbt file:

scalaVersion := "2.9.2"

To use Scala 2.10.0, put an entry like this in the build.sbt file:

If you're interested in the details of the translation scheme of a Scala for loop (for comprehension), here's a quick look at how a for loop is translated into, well, other code.

A simple Scala for loop

In a first example, we'll start with the following Scala class:

class Main {
  def foo { for(i <- 0 to 10) println(i) }
}

Next, I compile this class from the command line like this:

A friend of mine is currently unemployed, and as I've talked to her about ways to approach her situation, I'm reminded of how I started a consulting business named Mission Data.

A friend of mine is currently unemployed, and as I've talked to her about ways to approach her situation, I'm reminded of how I started a consulting business named Mission Data.

Back when I was interviewing for computer programming positions in Boulder and Louisville, Colorado, I found that many interviewers ask questions about Java serialization. After being asked about serialization for the third time, I remembered an old Java deep clone hack that takes advantage of serialization.

Like many other people, during the months of December and January I reflect on the year that's passed, and come up with some goals for the next year. Over the years this has led me to: