ScalaFlavor4J provides you Scala flavored useful API in Java.
ScalaFlavor4J is available on the maven central repository. Add the following dependency:
<dependencies>
<dependency>
<groupId>com.m3</groupId>
<artifactId>scalaflavor4j</artifactId>
<version>[1.1,)</version>
</dependency>
</dependencies>-
_(xxx)methods are removed because the name is deprecated in Java 8. Please useapply(xxx)instead. -
FunctionNare changed from abstract class to interface due to JSR-335 specification. If you want to usecomposeorandThen, please decorateFunctionNinstances withRichFunctionN.
In the beginning, please view this presentation. Sorry, We can't put iframe here.
First of all, just import the following package.
import com.m3.scalaflavor4j.*;
import static com.m3.scalaflavor4j.Predef.*; // optionalProvides scala.Function*.
Scala:
val getLength: Function1[String, Int] = (v: String) => v.length
val getLength: (String) => Int = (v: String) => v.length
val len = getLength("foo")
val len = getLength.apply("foo")ScalaFlavor4J on Java 8:
F1<String, Integer> getLength = (v) -> v.length();
int len = getLength.apply("foo"); // -> len : 3VoidFunction* does not exist in Scala.
VoidFunction1<Object> print = (v) -> System.out.println(v);
print.apply("foo"); // "foo"Provides scala.Option.
Scala:
val some = Option(3)
some.isDefined
some.orNull(null)
some.getOrElse(0)
some map { i => "found : " + i } getOrElse { "not found" }
some fold ("not found"){ i => "found : " + i }
val none: Option[Int] = Option.empty
none.isDefined
none.getOrElse(0)
none map { i => "found : " + i } getOrElse { "not found" }
none fold ("not found"){ i => "found : " + i }ScalaFlavor4J on Java 8:
Option<Integer> some = Option.apply(3);
some.isDefined(); // true
some.getOrNull(); // 3
some.getOrElse(0); // 3
some.map(i -> "found : " + i).getOrElse(() -> "not found");
// -> "found : 3"
some.fold("not found").apply(i -> "found : " + i);
// -> "found : 3"
Option<Integer> none = Option.apply(null); // or Option.none();
none.isDefined(); // false
none.getOrNull(); // null
none.getOrElse(0); // 0
none.map(i -> "found : " + i).getOrElse(() -> "not found");
// -> "not found"
none.fold("not found").apply(i -> "found : " + i);
// -> "not found"Provides scala.collection.Seq.
Scala:
val words = Seq("foo", "bar", "baz")ScalaFlavor4J on Java 8:
Using variable arguments:
import java.util.*;
Seq<String> words = Seq.apply("foo", "bar", "baz");Or apply existing java.util.List object:
List<String> wordList = Arrays.asList("foo", "bar", "baz");
Seq<String> words = Seq.apply(wordList);Back to java.util.List:
List<String> wordList = words.toList();Scala:
Seq(1, 2, 3, 4, 5) map { (i: Int) => (i * 2).toLong }
Seq(1, 2, 3, 4, 5) flatMap { (i: Int) => 1 to i } mkString(",")
Seq(Some(1), Some(2), None, Some(3), None, Some(4), Some(5)) flatMap { (e: Option[Int]) => e }ScalaFlavor4J on Java 8:
Seq.apply(1, 2, 3, 4, 5).map(i -> Long.valueOf(i * 2));
// -> Seq.apply(2L, 4L, 6L, 8L, 10L)
Seq.apply(1, 2, 3, 4, 5).flatMap(i -> SInt.apply(1).to(i)).mkString(",");
// -> "1,1,2,1,2,3,1,2,3,4,1,2,3,4,5"
Seq.apply(1, 2, null, 3, null, 4, 5).flatMap(i -> Option.apply(i)).mkString(",");
// -> "1,2,3,4,5"Scala:
Seq('b', 'c', 'd').foldLeft("a"){ (z: String, c: Char) => z + c }
Seq('b', 'c', 'd').foldRight("a"){ (c: Char, z: String) => z + c }ScalaFlavor4J on Java 8:
String s = Seq.apply('b', 'c', 'd').foldLeft("a", (z, c) -> z + c);
// -> s : "abcd"
String s = Seq.apply('b', 'c', 'd').foldRight("a", (c, z) -> z + c);
// -> s : "adcb"Scala:
Seq(1, 2, 3, 4, 5) filter { (i: Int) => i > 2 }ScalaFlavor4J on Java 8:
Seq.apply(1, 2, 3, 4, 5).filter(i -> i > 2);
// -> Seq.apply(3, 4, 5)Scala:
Seq(1, 2, 3, 4, 5) foreach { (i: Int) => println(i) }ScalaFlavor4J on Java 8:
Seq.apply(1, 2, 3, 4, 5).foreach(i -> println(i));
// -> "1" "2" "3" "4" "5"Provides scala.collection.parallel.ParSeq. ScalaFlavor4J does not support all the methods that are defined in Scala because some methods are not efficient.
Scala:
(1 to 1000).par.foreach { (i) => print(Thread.currentThread.getId + ",") }
(1 to 1000).par.map { (i) => print(Thread.currentThread.getId + ","); i * i }
(1 to 1000).par.flatMap { (i) => print(Thread.currentThread.getId + ","); 1 to i }ScalaFlavor4J on Java 8:
SInt.apply(1).to(1000).par().foreach(i -> println(Thread.currentThread.getId() + ","));
SInt.apply(1).to(1000).par().map(i -> {
println(Thread.currentThread.getId() + ",");
return i * i;
});
SInt.apply(1).to(1000).par().flatMap(i -> {
println(Thread.currentThread.getId() + ",");
return SInt.apply(1).to(i);
});Provides functions that are similar to for-comprehension.
Scala:
val xs1 = Seq("abc", "abcd", "abcde")
val xs2 = Seq(3, 4, 5)
val bs = for (a <- xs1; b <- xs2) yield a.length == bScalaFlavor4J on Java 8:
Seq<String> xs1 = Seq.apply("abc", "abcd", "abcde");
Seq<Integer> xs2 = Seq.apply(3, 4, 5);
Seq<Boolean> bs = For.apply(xs1, xs2).yield(tpl -> tpl._1().length() == tpl._2());
// true, false, false, false, true, false, false, false, trueProvides scala.collection.Map.
Scala:
val sMap = Map("Andy" -> 21, "Brian" -> 18, "Charley" -> 27)ScalaFlavor4J on Java 8:
Apply an existing java.util.Map object:
import java.util.*;
Map<String, Integer> ageList = new HashMap<String, Integer>();
ageList.put("Andy", 21);
ageList.put("Brian", 18);
ageList.put("Charley", 27);
SMap<String, Integer> sMap = SMap.apply(ageList);Back to java.util.Map:
Map<String, Integer> javaMap = sMap.toMap();Scala:
val age: Int = sMap.getOrElse("Denis", -1)ScalaFlavor4J on Java 8:
int age = sMap.getOrElse("Denis", -1);
// -> age : -1Scala:
sMap foreach { case (k, v) => println(k) }
val withoutCharley = sMap filter { case (k, v) => k.contains("n") }ScalaFlavor4J on Java 8:
sMap.foreach(v1 -> println(v1._1()));
// -> "Andy" "Brian" "Charley"
SMap<String, Integer> withoutCharley = sMap.filter(v1 -> v1._1().contains("n"));
// -> withoutCharley : ("Andy" -> 21, "Brian" -> 18)SMap<String, Integer> newMap = sMap.updated("Denis", 24);
// -> newMap : ("Andy" -> 21, "Brian" -> 18, "Charley" -> 27, "Denis" -> 24)
SMap<String, Integer> newMap = sMap.plus(Pair.apply("Denis", 24), Pair.apply("Elle", 19));
// -> newMap : ("Andy" -> 21, "Brian" -> 18, "Charley" -> 27, "Denis" -> 24, "Elle" -> 19)
SMap<String, Integer> newMap = sMap.minus("Charley", "Andy");
// -> newMap : ("Brian" -> 18)Scala:
val oneToFile: Seq[Int] = 1 to 5
val oneUntilFive: Seq[Int] = 1 until 5Java:
Seq<Integer> oneToFive = SInt.apply(1).to(5);
// -> oneToFive : Seq.apply(1, 2, 3, 4, 5)
Seq<Integer> oneUntilFive = SInt.apply(1).until(5);
// oneUntilFive : Seq.apply(1, 2, 3, 4)Provides scala.concurrent.ops._
Scala:
import scala.concurrent.ops._
spawn { println("on a different thread!") }ScalaFlavor4J on Java 8:
import static com.m3.scalaflavor4j.ConcurrentOps.*;
spawn(() -> println("on a different thread!"));Scala:
val f = future { Thread.sleep(1000L); "foo" }ScalaFlavor4J on Java 8:
java.util.concurrent.Future<String> f = future(() -> {
Thread.sleep(1000L);
return "foo";
});
f.get(); // -> "foo"Provides scala.util.control.Exception._.
Scala:
import scala.util.control.Exception._
val result: String =
catching(classOf[RuntimeException]) withApply {
(t) => "catched"
} apply {
throw new RuntimeException
}ScalaFlavor4J on Java 8:
import static com.m3.scalaflavor4j.ExceptionControl.*;
String result = catching(RuntimeException.class)
.withApply(t -> "catched")
.apply(() -> {
// return "ok"; -> result : "ok"
// throw new IOException(); -> will be thrown
throw new RuntimeException();
});Inspired by "Scala Automatic Resource Management"(Scala Incubator project), but not implemeneted exactly.
import static com.m3.scalaflavor4j.arm.Resource.*;
String content = managed(new FileInputStream("input.txt")).map(is -> "content");
// finally FileInputStream will be closedProvides scala.io.Source.
BufferedSource source = Source.fromFile("input.txt", "UTF-8");
BufferedSource source = Source.fromURL("http://docs.scala-lang.org/cheatsheets/", "UTF-8");
Seq<Byte> bs = source.toByteSeq():
Seq<Character> cs = source.toCharSeq():
Seq<String> lines = source.getLines();You can read more details abouts ScalaFlavor4J in Cookbook.
Copyright 2012 M3, Inc.
Apache License, Version 2.0