Scala

Scala is a functional, object-oriented language. Its name stands for SCAlable LAnguage. It runs on the JVM and integrates seemlessly with Java. The Twitter website famously rewrote their backend functionality in Scala and published the code under the Apache 2 license.

Wikipedia's canonical Hello World examples in Scala. Two ways of doing the same thing -

object HelloWorld extends Application {
   println("Hello, world!")
}

and this:

object HelloWorld {
   def main(args: Array[String]) {
      println("Hello, world!")
   }
}

To run the code from the newly installed Scala:

[greg:~] cd dev/src
[greg:src] mkdir scala
[greg:src] cd scala
[greg:scala] mkdir firstProject
[greg:scala] cd firstProject
[greg:firstProject] alias scala=/opt/scala-2.7.5.final/bin/scala 
[greg:firstProject] alias scalac=/opt/scala-2.7.5.final/bin/scalac
[greg:firstProject] scalac HelloScala.scala
[greg:firstProject] scala -classpath .: HelloScala
Hello, world!
[greg:firstProject] 

Although I added /opt/scala-2.7.5.final/bin to the system PATH variable in ~/.bash_profile, in order to invoke the compiler and the runtime, I found it necessary to alias the two scripts (see above).

Scala is described as a multi-paradigm language. It has the features of an object-oriented language and a functional language. Venkat Subramaniam shows how to run Scala code as Unix scripts by use of what is called the "sha-bang" (the #! ... !# portion of the text below) which is a command to the command line interpreter telling it that the script is to be run by the program named in the "sha-bang".

#!/usr/bin/env scala !#
println("Hello," + args(0)) 

If I save the above code in script.scala I can run it without directly invoking Scala:

[greg:firstProject] script.scala Greg
Hello,Greg
[greg:firstProject] 

Other Features of Scala

Scala allows you to define nested packages just like C++ and C# namespaces. You may define many packages and classes in one source file.

Scala's default access level is public. Scala's protected access is more restrictive than Java's, giving access only to derived classes. At the Package level, control is more granular than Java's.

Combining Functional and Object Oriented Paradigms

package Cars {

 package Sport {
  class Porsche {
   def go() = 100 
  }
 }

 package Economy {
  class Corolla {
   def go() = 50 
  }
 }
}

object Car {
 def main(args: Array[String]) {
  val car1 = new Cars.Sport.Porsche();
  val car2 = new Cars.Economy.Corolla();
  println(car1.go())
  println(car2.go())
 }
}

[greg:firstProject] scalac Cars.scala
[greg:firstProject] ls -l
total 56
-rw-r--r--  1 greghelton  staff  1030 Jul 26 22:03 Car$.class
-rw-r--r--  1 greghelton  staff   566 Jul 26 22:03 Car.class
drwxr-xr-x  4 greghelton  staff   136 Jul 26 22:03 Cars
-rw-r--r--@ 1 greghelton  staff   316 Jul 26 21:59 Cars.scala
[greg:firstProject] ls cars
Economy Sport
[greg:firstProject] ls Cars/Sport
Porsche.class
[greg:firstProject] ls Cars/Economy
Corolla.class
[greg:firstProject]  scala Car
100
50
[greg:firstProject]