Andreas Enbohm Capgemini Sverige AB Scala or ”The Free Lunch is Over”

© 2004 Capgemini - All rights reserved 2008, July – Andreas Enbohm Why Scala  The free lunch is over...  Today – 2 Cores  2010 maybe 12 (AMD), in 5 years maybe 16  Difficult to utilize several CPUs with Java  Huge API in current Java – some argue it may collape due to its own weight  Scala = ScalableLanguage  Designed to fit todays and some of tomorrows programming paradigms  Actors – Easier to utilize than memory synchronization (more about this later)  Nice (less boiler plate code) syntax and ’type safe duck typing’  And much more...

© 2004 Capgemini - All rights reserved 2008, July – Andreas Enbohm Scala - Features  OO and functional language ”a general purpose programming language designed to express common programming patterns in a concise, elegant, and type-safe way”  Functional language – (often) no side effect, avoids state and mutable data, i.e functions can run independently and without knowlegde of eachother  Open Source  Compact code, ca 50 % less code than Java  Static typed language (but with ’kind of’ duck typing, more about this later)  Pattern matching, singel inheritance, immutable collections (like Java Strings), XML as FCC  SUnit, Lift (web framework), Support for Maven, Ant, Plugins for Eclipse, Netbeans, IntelliJ  Why not Ruby, Groovy, F#? - Fully interoperable with Java (call Java classes whenever you want) - Refactoring (static typed) - runs on world’s best VM! - very simple to inherit from Java classes - Javas annotations, threads, for each, it all works - Very fast (600x faster than groovy, lift 6x faster than Rails?) def sum(a:Int,b:Int) = a+b

© 2004 Capgemini - All rights reserved 2008, July – Andreas Enbohm Scala – Compared to Java  Defining a class  Everything in Scala is an Object! This also includes functions class Person(var firstName: String, var lastName: String) { } public class Person { private String firstName; private String lastName; public Person(String firstName, String lastName) { this.firstName = firstName; this.lastName = lastName; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; }

© 2004 Capgemini - All rights reserved 2008, July – Andreas Enbohm Scala – Compared to Java  Defining variables - ; and type can often be omitted  Creating objects  List is of type List[String] by default  List objects in Scala contains several useful functions to access elements in the List  Ommiting some dots… val myInt: Int = 1; val anotherInt = 2 val anObject = Object //Omit () if you want just ’cluttering’ your code val aList = List(”John Doe”, ”Jane Doe”, ”Baby Doe”) println("Hi, " +aList.tail.head) //Prints “Hi, Jane Doe” List aList = new ArrayList (); //Java syntax for creating a list-object val aList = List //Scala syntax for creating corresponding list val aList = List[String] //Also works, notice just ONE generic definiton import java.util.{Date,Locale} import java.text.DateFormat import java.text.DateFormat._ val now = new Date val df = getDateInstance(LONG, Locale.FRANCE) println( df format now) //same as df.format(now)

© 2004 Capgemini - All rights reserved 2008, July – Andreas Enbohm Scala – Compared to Java  Exceptions - Scala has no checked exception (unlike Java but like C#) - If used with Java, use  Using pattern matching and functions  Scala uses ’traits’ which can be compared to interfaces. Can have implementations (but no state) try { doSomething(params) } catch { case ex: IOException => println("Oops! Some file is probably missing") case ex: NullPointerException => println(“Dohh!! Must initialize the variable ") } object MatchTest1 extends Application { def matchTest(x: Int): String = x match { case 1 => "one" case 2 => "two" case _ => "many" } println(matchTest(1)) //Prints “one” println(matchTest(99)) //Prints “many” }

© 2004 Capgemini - All rights reserved 2008, July – Andreas Enbohm Duck Typing in Scala  ”If it walks like a duck and quacks like a duck, then I would call it a duck.” – Wise Guy  Statically typed language don’t offer this flexibility (Java, C#) - i.e. no ’Duck Typing’  Downside – what happens if object does not have a ’quack’-method -> RuntimeException!  In Java, we must add an interface with method ’quack()’ – impossible to add an interface without changing the class! class Duck { public void quack() { print(”Duck Quacking!”) } class Person { public void quack() { print(”Person Quacking!”) } Duck d = new Duck(); Person p = new Person(); testQuack(d); testQucak(p); testQuack(duckableObject) { duckableObject.quack(); //Lets hope this work!!! }

© 2004 Capgemini - All rights reserved 2008, July – Andreas Enbohm Duck Typing in Scala  However Scala offers ’Structual Typing’ – a.k.a. Type safe duck typing  Consider following example (Scala syntax)  Scala offers structual typing, i.e. def getName() in test  The structual type ’getName()’ checks at compile time that ’aFileObject’ has a getName() method if not – compile error  If getName() is needed more than one, use traits. class File(name: String) { def getName(): String = name def open() { /*..*/ } def close() { println("close file") } } def testPrintName(aFileObject: { def getName(): String }) { println(aFileObject.getName) } testPrintName(new File("test.txt")) testPrintName(new java.io.File("test.txt")) trait HasName { def getName() : String } def testPrintName(HasName f) = { println(f.getName) }

© 2004 Capgemini - All rights reserved 2008, July – Andreas Enbohm Actors  ”Don't bring the grape juice into the living room“ – Brian Goetz  Java threads - shared memory, i.e. only one thread can operate on a shared resource concurrently - expensive to create, i.e. every thread has a high memory consumption - context switch. i.e a Java thread maps to a OS thread (limited numbers ~3K) - context switch make page faults - > slow due to thread needs to re-read data from RAM - difficult to use, i.e. deadlocks, raise conditions, live locks, NASA Mars explorer experied live lock - synchronize, i.e. not just a a monitor/lock but also write to main memory (no registers) ~100 slower! - Java was designed for single processors, not multi-cores!  Actor based concurrency - concurrenct processes communicates by exchanging messages - asynchronous message passing - ’share-nothing’-model - Erlang early to implement this style of concurrency - Erlang based web server ~80000 clients, Apache ~4000 clients  Two flavours in Scala; - Thread based actors – high level abstraction of threads which replaces error-prone shared memory access - Thread less actors – offers enourmous scalability. Lightweight processes are used as actors with much less overhead than a usual thread. ’Piggy-backs’ on calling threads stack trace (continuation closure)

© 2004 Capgemini - All rights reserved 2008, July – Andreas Enbohm Downsides  ”With great power comes great complexity” – James Gosling  New languages difficult to introduce to organisations  Not ready for prime time?

© 2004 Capgemini - All rights reserved 2008, July – Andreas Enbohm Questions?