An Introduction to Scala

An Introduction
to Scala
Dallas, TX
March 07, 2012

Discussion document – Strictly Confidential & Proprietary

Agenda …

The four W’s plus an H

• What: Scala Intro

• When: Scala History

• Who: Scala Implementations

• Why: A Case for Scala

• How: The Basics of Scala

– Getting Up and Running

– Classes and Objects

– Functional Programming

– Traits and Mixins

– Java in Scala

– Scala in Java

An Introduction to Scala
March 7, 2012 2

Agenda …

Goals

• Have an understanding of what Scala is

• Have an interest in learning more

• Go install Scala!

March 7, 2012 3

What: Scala Intro …

What is Scala?

Scala is a general purpose programming language designed to express common programming
patterns in a concise, elegant and type-safe way. It smoothly integrates features of object-
oriented and functional languages, enabling Java and other programmers to be more
productive. Code sizes are typically reduced by a factor of two to three when compared to an
equivalent Java application.

• Origin of name is two-fold
– Scala is Italian for staircase. Scala is considered a “step up” from other languages
– SCAlableLanguage
• Seamless integration with Java. Runs in the JVM
• Proven performer in high transaction, highly scalable environments
• Developers can follow an imperative or functional style
• ThoughtWorks has put Scala in the “trial” radar category (July 2011)

March 7, 2012 4

When: Scala History …

Scala History … 1995 to 2012

Brief history of Scala
• Developed by Martin Odersky
– 1995 he learned of Java and wrote functional language that compiled to Java bytecode - Pizza
– Pizza evolved into what we now recognize as Java generics
• Sun approached Odersky in 1997 to write Java 1.1 compiler
• Odersky led javac development from Java 1.1 through 1.4
• In 1999, Odersky joined EPFL to conduct research into improving functional and OO languages
• Design of Scala began in 2001 and first release was in 2003
• Early releases of compiler written in Java
• Version 2.0.0 introduced a completely rewritten compiler in Scala
• Current version 2.9.1 released in August 2011

March 7, 2012 5

Who: Scala Implementations …

Scala is finding a home in high transaction environments

• Twitter Kestrel – Twitter’s message queue server
– Ported from RoR
• FourSquare – Message queue, website, mobile
website and RESTful API
• LinkedIn – Public and backend RESTful API’s
– Ported from RoR
• Novell – Pulse, a cloud-based, real-time
collaboration platform for the enterprise

March 7, 2012 6

Why: A Case for Scala …

Is Scala a fit?

Upside of Scala
• Ease of integration with existing Java environments
• When a functional style is utilized, scales easily
• Performance is equivalent, and in some cases, better than Java
• Good candidate for medium risk greenfield projects
• Learning curve is not massive, as Scala follows Java syntax

Downside of Scala
• Toolset is immature
– IDE integration is weak, but improving
– Java profiling tools can be used, but difficult
• Overcoming Java footprint will be difficult. It’s comfortable and works. It’s the COBOL/C+ of our
generation
• User acceptance still low due to lack of knowledge and reasons listed above

March 7, 2012 7

How: The Basics of Scala...

What you need to know to get started!

• Getting Up and Running

• Building Blocks

• Classes and Objects

• Functional Programming

• Traits and Mixins

• Java in Scala

• Scala in Java

March 7, 2012 8

How: The Basics of Scala …

Getting up and running

Required
• Java 1.5 or greater
• Scala 2.9.1 distribution

Optional
• SBT – Simple Build Tool
• IDE Plugin
– ScalaIDE (Eclipse – must use Helios)
– Scala Plugin for IntelliJ IDEA
– Scala Plugin for NetBeans

Notes:
1) Installation of Scala and SBT involve expanding compressed file and adding to PATH
2) IDE installation varies by tool; some dependency on IDE release number
3) ScalaIDE officially supported by Typesafe

March 7, 2012 9


Building Blocks

Declarations - var
• A var is similar to a non-final variable in Java
• If type is not declared, it will be inferred from the assigned object
• Once initialized, it can be reassigned (mutable), but type cannot change
• Object can be assigned at any time

Example
classVarA(n:Int) {
varvalue =n
}

classVarB(n:Int) {
valvalue =newVarA(n)
}

objectExampleVar {
varx=newVarB(5)
x=newVarB(6)
// x.value = new VarA(7)
x.value.value=7
}
March 7, 2012 10


Building Blocks

Declarations - val
• A val is similar to a final variable in Java
• Once initialized, it can not be reassigned (immutable)
• Object must be initialized at declaration
• Object cannot be reassigned, but internal state can be modified

Example
classValA(n:Int) {
varvalue =n
}

classValB(n:Int) {
valvalue =newValA(n)
}

objectExampleVar {
valx=newValB(5)
x.value.value=6
}

March 7, 2012 11


Building Blocks

Declarations - def
• A defis used to define a function
• A comma-separated list of parameters in parentheses follows the name
• The type of the return value must be defined following the parameters
• If a return type is not included, you are defining a “procedure”
• The equals sign hints to the fact a function defines an expression resulting in a value
• The final value of the control block is the return value

Example
classExampleDef(n:Int, a:Int, b:Int) {
valvalue =n + max(a,b)

defmax(x:Int, y:Int):Int={
if(x>y) x
elsey
}
}

March 7, 2012 12

How: The Basics of Scala… Classes and Objects …

Classes

Class
• A class in Scala looks similar to a class in Java – minus the boilerplate code
• Public by default
• Getters and setters defined by variable declaration

Example
classCoordinate() {
vardegrees =0.0
varminutes =0.0
varseconds =0.0

defasDegrees=degrees + minutes/60.0+ seconds/60.0/60.0
defasRadians=asDegrees.toRadians
}

objectExample extendsApp {
vallatitude =newCoordinate
latitude.degrees=32.0
latitude.minutes=57.0
latitude.seconds=30.762
}
March 7, 2012 13

How: The Basics of Scala … Classes and Objects …

Classes

Class – Primary Constructor
• More concise
• val has getter only
• Primary constructor creates the fields

Example
classCoordinate(valdegrees:Double, valminutes:Double, valseconds:Double) {
}

vallatitude =newCoordinate(32.0, 57.0, 30.762)
vallongitude =newCoordinate(96.0, 49.0, 25.1076)
println(latitude.degrees) // prints 32.0
}

March 7, 2012 14

How: The Basics of Scala … Classes and Objects …

Classes

Class – Auxiliary Constructor
• Auxiliary constructor is created as a def this
• Must start with a call to a previously defined auxiliary or primary constructor

Example
defthis(degrees:Double, minutes:Double) =this(degrees, minutes, 0.0)
defthis(degrees:Double) =this(degrees, 0.0)
defthis() =this(0.0)

}

vallatitude =newCoordinate(32.0)
vallongitude =newCoordinate(96.0, 49.0)
println(latitude.minutes) // prints 0.0
println(longitude.minutes) // prints 49.0
}

March 7, 2012 15

How: The Basics of Scala… Classes and Objects …

Objects

Object
• Creates a singleton of a class
• Can be used as a home for miscellaneous functions
• No constructor parameters

Example
objectCrederaLatitudeextendsCoordinate {
this.degrees=32.0
this.minutes=57.0
this.seconds=30.762
defprintCoordinate=println(this.asDegrees)
}
defthis(degrees:Double, minutes:Double) =this(degrees, minutes, 0.0)
defthis(degrees:Double) =this(degrees, 0.0)
defthis() =this(0.0)

}

CrederaLatitude.printCoordinate// prints 32.958545
}

March 7, 2012 16

How: The Basics of Scala … Functional Programming …

Functional programming… defined

Definition
• Treats computations as the evaluation of mathematical functions
• Avoids state and mutable data
• Calling a function twice, with the same arguments, should produce the same results both times
• First-class functions are functions that either take other functions as arguments or return them as
results
• In Scala, a function literal (the definition) is compiled to a functional value (a class)
• Functional values can be assigned to a val or var. If assigned to a var, it is mutable.

Example
varincrease =(x:Int) =>x + 1
valresult0=increase(10) // results in 11

March 7, 2012 17


Functional programming… defined

Definition
• Treats computations as the evaluation of mathematical functions
• Avoids state and mutable data
• Calling a function twice, with the same arguments, should produce the same results both times
• First-class functions are functions that either take other functions as arguments or return them as
results
• In Scala, a function literal (the definition) is compiled to a functional value (a class)
• Functional values can be assigned to a val or var. If assigned to a var, it is mutable.

Example
varincrease =(x:Int) =>x + 1
valresult0=increase(10) // results in 11

increase =(x:Int) =>x + 10
valresult1=increase(10) //results in 20

March 7, 2012 18


Passing functional values

Passing as a value
• Functional values can be passed as a value into another function
• Common use is to make calls on the immutable collection List

Example
valsomeNumbers=List(-22,-19,-12,-9,-2,0,1,5,9,32)
valprintList=(x:Int) =>println(x)
println("print all numbers: ")
someNumbers.foreach(printList)

println("-----------------------------------")

March 7, 2012 19


Passing functional values

Passing as a value
• Functional values can be passed as a value into another function
• Common use is to make calls on the immutable collection List

Example
valsomeNumbers=List(-22,-19,-12,-9,-2,0,1,5,9,32)
valprintList=(x:Int) =>println(x)
println("print all numbers: ")
someNumbers.foreach(printList)

println("-----------------------------------")
println("print only positive numbers:")

valfilterList=(x:Int) =>x>0
someNumbers.filter(filterList).foreach(printList)

March 7, 2012 20

How: The Basics of Scala … Traits and Mixins …

Traits and Mixins

Trait
• Scala developers saw inherent problems with Java interfaces
• Scala solution is a combination of Java interfaces and Ruby mixins called traits
• Like an object, traits do not have constructors
• Added to class via the extends keyword
• Additional traits can be “mixed in” via the with keyword

March 7, 2012 21

How: The Basics of Scala … Java in Scala …

Integration

Java in Scala importorg.joda.time._
• Add jar to your CLASSPATH
traitCurrentTime {
• Import package or class valnow =newDateTime()
• Implement an object using the class }

March 7, 2012 22

How: The Basics of Scala … Java in Scala… Scala in Java …

Integration

Java in Scala importorg.joda.time._
• Add jar to your CLASSPATH
traitCurrentTime {
• Import package or class valnow =newDateTime()
• Implement an object using the class }

Scala in Java
importcom.credera.tech.scala.*;
• Compile to a jar
• Add jar to your CLASSPATH public classHello {
public static void main(String[] args) {
• Import package or class
System.out.println("Hello, this is java.");
• Implement an object using the class CrederaOffice.printOfficeLocation();
}
}

March 7, 2012 23

Appendix … Web References ...

Resources

Web Resources
Description Link
Scala http://www.scala-lang.org
SBT – Simple Build Tool http://github.com/harrah/xsbt
ScalaIDE for Eclipse http://scala-ide.org
Scala Plugin for IntelliJ IDEA http://confluence.jetbrains.net/display/SCA/Scala_Plugin+for+IntelliJ+IDEA
Scala Plugin for NetBeans http://wiki.netbeans.org/Scala
ThoughtWorks Technology Radar http://thoughtworks.com/radar
Indeed.com Scala Job Trends http://indeed.com/jobtrends?q=scala&l=&relative=1
Twitter’s Scala Experience http://web2expo.com/webexsf2009/public/schedule/detail/6110
LinkedIn’s Scala Experience http://infoq.com/articles/linkedin-scala-jruby/voldement
Java Interfaces Discussion http://www.codecommit.com/blog/scala/scala-for-java-refugees-part-5

March 7, 2012 24

Contact ...

Contact Me!

blemons@credera.com

@brentlemons

slideshare.net/brentlemons

March 7, 2012 25

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