Englishman in new york => scala for java developer

5/18/13 5:22 PMEnglishman in New York - Scala for Java Developer

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ENGLISHMAN IN NEWENGLISHMAN IN NEWYORKYORK

Scala for Java Developer => Personal Experience



WHO IS THIS GUY?WHO IS THIS GUY?12+ yeas in Java Development

JEEconf , speakerUA Web Challenge , , , judge

Java Stage Producer

Skype: anton.naumow

2011 2012I II III IV

HotCode

[email protected]

@antonnaumovua.linkedin.com/in/antonnaumov/

http://corwin.calepin.co

http://jeeconf.com/archive/jeeconf-2011/speakers/

http://jeeconf.com/archive/jeeconf-2012/speakers/

http://i.uwc.org.ua/about-project

http://ii.uwc.org.ua/judges

http://iii.uwc.org.ua/judges

http://uawebchallenge.com/

http://hotcode.org/

mailto:[email protected]

https://twitter.com/antonnaumov

http://ua.linkedin.com/in/antonnaumov/

http://corwin.calepin.co/



WHY SCALA?WHY SCALA?Buzz word?

Modern technology

Respect

New knowledge and new challenge



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



GETTING STARTEDGETTING STARTED... def sum(bars: Iterable[Bar]): Long = { bars.filter(_.type == SOME).foldLeft(0L)(_ + _.amount) }...



GETTING STARTEDGETTING STARTED



TRY ONCE MORETRY ONCE MOREDaniel Spiewak "Scala for Java Refugees"

http://www.codecommit.com/blog/scala/scala-for-java-refugees-part-1



LIGHT SIDELIGHT SIDE



OPTIONOPTIONI think its no NullPointerExceptions anymore

... Option(getBar("foo")) def bar(index: java.lang.Integer): Option[Int] = { Option(index) match { case value: Some => value case None => None }}...



TUPPLETUPPLEUp to 22 arguments. No stupid classes. No arrays.

No guessing.

... def bar(pattern: String):(Int, String) = (pattern.length, pattern)...



MATCHMATCHIt's something like switch... but much better

... (number, string) match { case (1, "test") => ... case (_, "another test") => ... case _ => ... }...



COLLECTIONSCOLLECTIONSSome magic happens here

... final Collection<Integer> coll = Lists.newArrayList(1, 2, 3, 4, 5);... for (final int item : coll) { if (item == 5) { return item; } } return -1;...

... val coll = Seq(1, 2, 3, 4, 5)... coll.find(_ == 5) match { case Some(item) => item case None => ... }...



EXCEPTION HANDLINGEXCEPTION HANDLINGSomething like Java 1.9

... try { //some code throws exceptions catch { case e: IllegalAccessException => ... case e: Exception => ... }...



TRAITTRAITNo comments

trait First { def convert(input: String): String } trait Second { def out(input: String) => System.out.println(bar(input)) } class Third extends First with Second { override def convert(input: String): String => input.toLowerCase() }... val obj = new Third obj.out("HeLlO TrAiTs!")



MULTITHREADINGMULTITHREADINGSimple. More simple. The simplest

Iterable[String] seq = Seq("one", "two", "three") seq.par.map { str => str.toUpperCase() }



XMLXMLLike a charm

val xml = <root> <node name="first">Some text</node> <node name="second">Some other text</node> </root>

... val source = XML.load(IOUtils.toInputStream(xml) (source \ "node" \ "@name").text match { case "first" => "First node found" case _ => (source \ "node").text...



DARK SIDEDARK SIDE



COMPILATION TIMECOMPILATION TIMEScala code compiles about 30% longer than Java code



CODE READABILITYCODE READABILITYSomekind like this still mess a point

def parseResponse(response: String): Map[String, String] = { (for (param <- response.split("&"); trimmed = URLDecoder.decode(param.trim, "UTF-8"); if (!trimmed.isEmpty) yield { (trimmed.split("=", 2).toList: @unchecked) match { case key :: value :: Nil => key -> value case key :: Nil => key -> null } }).toMap



OPERATOR OVERRIDING, IMPLICITOPERATOR OVERRIDING, IMPLICITNot obvious language constructions always MAY produce a

mess

And always will produce a mess



NO BACKWARD COMPATIBILITYNO BACKWARD COMPATIBILITYScala 2.9 code produce an runtime exception running with

Scala 2.10



DIAMOND PROBLEMDIAMOND PROBLEMMultiple inheritance solution is architecture bomb



TOP 3 SCALA FEATURESTOP 3 SCALA FEATURESSomething not obvious but very useful



MODELMODEL class Fee { public Long getAmount() { return amount; } public void setAmount(final Long amount) { this.amount = amount; } public String getType() { return type; } public void setType(final String type) { this.type = type; }

private Long amount; private String type; }



COLLECTION FILTERINGCOLLECTION FILTERINGJAVAJAVA

... public long sumFeesByType(final Collection<Fee> fees, final String type) { long sum = 0; for (final Fee fee : fees) { if (fee != null && fee.getType() .equalsIgnoreCase(type)) { sum += fee.getAmount() == null ? 0L : fee.getAmount() } } return sum; }...



COLLECTION FILTERINGCOLLECTION FILTERINGSCALASCALA

... def sumFeesByType(fees: util.Collection[Fee], feeType: String) fees .filter(_.getType.eqaualsIgnoreCase(feeType) .foldLeft(0L)(_ + _.getAmount)...



OPTION AS COLLECTIONOPTION AS COLLECTION... val amount = fees.find(_.getType.equalsIgnoreCase("PROMO")) .map(_.getAmount).getOrElse(0L)...



VALUE CONVERSIONVALUE CONVERSIONJAVAJAVA

public final class FeeExtension { private FeeExtension() {} public static long getFeeAmount(fee: Fee) { return fee.getAmount() == null ? 0L : fee.getAmount(); } }... import FeeExtension.*... final long amount = getFeeAmount(fee);...



VALUE CONVERSIONVALUE CONVERSIONSCALA :: IMPLICIT + OBJECTSCALA :: IMPLICIT + OBJECT

class FeeExtension(fee: Fee) { def amount: Long = Option(fee.getAmount) match { case Some(value) => value case None => 0L } }

object FeeExtension { implicit def extendsFee(fee: Fee) = new FeeExtension(fee) }... import FeeExtension._... val amount = fee.amount...



VALUE CONVERSIONVALUE CONVERSIONSCALA ::: PACKAGE OBJECTSCALA ::: PACKAGE OBJECT

package com.github.sample; package object sample { def amount(fee: Fee) = Option(fee) match { case Some(value) => value case None => 0L }... package com.github.sample;... val amount = fee.amount...



RESUMERESUMEScala or Not Scala?



THANK YOU!THANK YOU!

Englishman in new york => scala for java developer

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