JarCastingFunctional helpers for java
This project is a really simple functional library. It provides only the building blocks that I lacked while working on a project. It is mostly inspired by what I've seen and used in the Scala language.
Get it
<dependency>
<groupId>fr.sertelon.fp</groupId>
<artifactId>func-helper</artifactId>
<version>2.0.0</version>
</dependency>
Features
Opt
Option[T] is a very handy structure in Scala. Guava has its own Optional, but I didn't want to depend on any big lib. Thus, Opt
public class Option {
Function<Integer, String> intToString = input -> String.valueOf(input);
Function<String, Boolean> isEmpty = input -> input.isEmpty();
public Option() {
Opt<Integer> intOpt = toOpt(null); // => None
Opt<Integer> intOpt2 = toOpt(3); // => Some(3)
Opt<Integer> choose = intOpt.or(intOpt2); // => Some(3)
Opt<String> map = choose.map(intToString); // => Some("3")
map.isDefined(); // => true
intOpt.getOrElse(3); // => 3
intOpt.get(); // => NoSuchElementException
Opt<String> strOpt = toOpt((Object) "3").asOpt(String.class);
toOpt("").filter(isEmpty); // => None
Opt<Integer> noneOpt = none();
}
}
IList
This construct is an immutable linked list. It is based on the same implementation as Scala's List.
public class ImmutableList {
public ImmutableList() {
nil(); // => empty list
IList<Integer> l = list(1, 2, 3); // => List(1,2,3)
range(0, 3); // List(0,1,2)
rangeIncl(0, 3); // List(0,1,2,3)
l.get(1); // => 2
l.head(); // => 1
l.tail(); // => List(2,3)
l.isEmpty(); // => false
l.reverse(); // => List(3,2,1)
l.mkString("-"); // => 1-2-3
l.mkString("[", ":", "]"); // => [1:2:3]
l.prepend(0); // => List(0,1,2,3)
l.map(intToString); // => List("1","2","3")
l.filter(isOdd); // => List(1,3)
l.foreach(print); // => prints 1, then 2, then 3
l.foldLeft(0, sum); // => 6
}
Function<Integer, String> intToString = input -> String.valueOf(input);
Function<Integer, Boolean> isOdd = input -> input % 2 == 1;
Function<Integer, Nothing> print = input -> {
System.out.println(input);
return nothing;
};
BiFunction<Integer, Integer, Integer> sum = (i1, i2) -> i1 + i2;
}
Try
This structure allows you to return success or failure information.
public class TryStructure {
public TryStructure() {
Try.emptySuccess(); // => Success<Nothing>(nothing)
Try.failure(new Exception()); // => Failure<Exception, Object>
Try.success(Integer.valueOf(2)); // => Success<Integer>(2)
strToDouble.apply("2.34"); // => Success<Double>(2.34)
strToDouble.apply("xxxx"); // => Failure(NumberFormatException, Double>
strToDouble.apply("2.34").map(doubleToStr); // => Success<String>("2.34")
IList<Try<Integer>> l = list(success(1), success(2), success(3));
Try<IList<Integer>> tl = Try.sequence(l); // => Success(List(1,2,3))
}
FTry1<String, Double> strToDouble = input -> {
try {
return success(Double.valueOf("xxx"));
} catch (NumberFormatException e) {
return failure(e);
}
};
FTry1<Double, String> doubleToStr = input -> Try.success(input.toString());
}
Utils
public class Utils {
public Utils() {
// Tuple2
T2<String, Long> tuple = t2("hello", 2L);
String hello = tuple._1; // "hello"
Long two = tuple._2; // 2
// Predef functions. Useful functions commonly used
Predef.isStrEmpty.apply(""); // true
Predef.isStrNotEmpty.apply(""); // false
Predef.objToString.apply(2); // "2"
}
}
Roadmap
If someone else than me is to use this library, I'm open to feedback! Will add whatever I'd like to use in Java, as long as I can keep this lib lightweight, otherwise, I should be better off using an existing one.
License
Copyright Romain Sertelon 2013
This software is licenced under the Apache Software License v2.0, you can find it in the LICENCE file.