ScalaFlavor4J- Scala flavored API in Java -

Kazuhiro Sera @seratch

What’s this?

• github.com/m3dev/scalaflavor4j

• A pure Java library

• NOT a wrapper of scala-library.jar

• Function, Seq, Range, Option, Map, ParSeq...

• Already used by some apps at M3, Inc.

Motivation

• “For fun”

• To get along with legacy Java systems

• Help co-workers ease into Scala (showing them that Scala has a lot of useful APIs)

• Might be useful as a Scala educational tool for Java programmers

Function

// val getLength = (str: String) => if (str == null) 0 else str.length// val len = getLength(“foo”)

import com.m3.scalaflavor4j.*;F1<String,Integer> getLength = new F1<String,Integer>() { public Integer _(String str) { // apply method definition return str == null ? 0 : str.length(); }};final int len = getLength.apply(“foo”); // -> 3final int len = getLength._(“foo”); // -> 3

Option

// val opt = Option(“something”)

Option<String> opt = Option._(“something”);opt.isDefined(); // -> trueopt.getOrNull(); // -> “something”Option<String> none = Option._(null);none.getOrElse(“”); // -> “”

opt.map(new F1<String,String>() { ... }) // apply F1 if Some .getOrElse(new F0<String>() { ... }); // apply F0 if None

Example(Option)

class UserService { public User findById(String id) { return DB.findUserById(id); }}User user = userService.findById(“123”)); // user might be null↓class UserService { public Option<User> findById(String id) { return Option._(DB.findUserById(id)); } // Explicitly state that User might be null}

Seq

// val seq = Seq(1,2,3,4,5)

Seq<Integer> seq = Seq._(1,2,3,4,5)

import java.util.*;List<Integer> javaList = Arrays.asList(1,2,3,4,5);Seq<Integer> seq = Seq._(javaList);javaList = seq.toList();

#map(F1)

// val values = Seq(1,2,3,4,5) map { i => i *i }

Seq<Integer> values = Seq._(1,2,3,4,5).map( new F1<Integer, Integer>() { public Integer _(Integer i) { return i * i; } }); // -> 1,4,9,16,25

#flatMap(F1)

// val values = Seq(1,2,3) flatMap { i => 1 to i }

Seq<Integer> values = Seq._(1,2,3).flatMap( new F1<Integer, CollectionLike<Integer>>() { public Seq<Integer> _(Integer i) { return SInt._(1).to(i); } }); // -> 1,1,2,1,2,3// * CollectionLike accepts Seq and Option

#filter(F1)

// val values = Seq(1,2,3,4,5) filter { i => i > 1 }

Seq<Integer> values = Seq._(1,2,3,4,5).filter( new PredicateF1<Integer>() { public Boolean _(Integer i) { return i > 1; } }); // -> 3,4,5

// * PredicatedF1<A> is just an alias of F1<A,Boolean>

#foldLeft(F2)

// val values = Seq(1,2,3,4,5).foldLeft(0){ (z,i) => z + i }

Seq<Integer> values = Seq._(1,2,3,4,5).foldLeft( new FoldLeftF2<Integer,Integer>() { public Integer _(Integer z, Integer i) { return z + i; } }); // ->15

// * FoldLeft2<A,B> is just an alias of F2<A,B,A>

#foreach(VoidF1)

// Seq(1,2,3) foreach { i => println(i) }

Seq<Integer> values = Seq._(1,2,3).foreach( new VoidF1<Integer>() { public void _(Integer i) { System.out.println(i); } }); // -> Displayed “1” “2” “3”

Example(Seq)

List<Integer> input = Arrays.asList(3,2,5,0,4,1);List<Integer> result = new ArrayList<Integer>();for ( Integer i : input ) { if ( i != null && i > 2 ) { result.add(i * i); }}↓Seq._(input).filter(new PredicateF1<Integer>() { public Boolean _(Integer i) { return i != null && i >2; }}).map(new F1<Integer, Integer>() { public Integer _(Integer i) { return i * i; }}).toList(); // No mutable state, Separation

ParSeq

// val values = (1 to 100).par.map { i => i *i }

Seq<Integer> values = SInt._(1).to(100).par().map( new F1<Integer, Integer>() { public Integer _(Integer i) { System.out.println(Thread.currentThread.getId()); return i * i; } // Using Fork/Join framework(Available on JDK6) }); // -> 1,4,9,16,25

Range

// val range: Seq[Int] = 1 to 10// val range: Seq[Long] = 1L to 10LSeq<Integer> range = SInt._(1).to(10);Seq<Long> range = SLong._(1).until(11);

for(int i=0; i<10; i++) { ... }↓SInt._(0).until(10).foreach { ... }

Map

// val map = Map(1 -> “foo”, 2 -> “bar”)

import java.util.*;Map<Integer, String> javaMap = new HashMap<>();SMap<Integer, String> map = SMap._(javaMap);

// map,flatMap,filter,foreach, etc. are availablemap.filter(new PredicateF1<Tuple2<Integer,String>>() {...});map.map(new F1<Tuple2<Integer,String>>() {...});

ConcurrentOps

// import scala.concurrent.ops._// spawn { println(“On a different thread!”) }

new Thread(new Runnable() { public void run() { System.out.println(“On a different thread!”);}}).start();↓import static com.m3.scalaflavor4j.ConcurrentOps.*;spawn(new VoidF0() { public void _() { System.out.println(“On a different thread!”);}}); // using Fork/Join

ExceptionControl

// import scala.util.control.Exception._// val result = catching(classOf[Exception]) withApply {// (t: Throwable) => “ng”;// } apply { “ok” }

import static com.m3.scalaflavor4j.ExceptionControl.*;String result = catching(Exception.class) .withApply(new F1<Throwable>() { public String _(Throwable t) { return “ng”; } }) .apply(new F0<String>() { public String _() { return “ok”; } });

Example(catching)

String result;try { result = “ok”;} catch (AException ae) { result = “ng”; } catch (BException be) { result = “ng”; }↓String result = catching(AException.class, BException.class) .withApply(new F1<Throwable>() { public String _(Throwable t) { return “ng”; } }) .apply(new F0<String>() { public String _() { return “ok”; } });

andThen(You)

• More information -> https://github.com/m3dev/scalaflavor4j

• Feature requests welcome

• Pull requests welcome

• Let’s enjoy Java with ScalaFlavor4J!