jOOλ is part of the jOOQ series (along with jOOQ, jOOX, jOOR, jOOU) providing some useful extensions to Java 8 lambdas. It contains these classes:
Why only Function
and BiFunction
? We have also included support for Function1
through Function16
.
Tuple support is essential in functional programming. A variety of things can be modelled as tuples, e.g. function argument lists. This is why we support type safe Tuple1
through Tuple16
types.
The new Streams API was implemented to provide filter/map/reduce-like operations leveraging the new lambdas.
Many of the useful methods that we know from other functional languages (e.g Scala) are missing. This is why jOOλ knows
a Seq
(short of Sequential) interface that extends Stream
and adds a variety of additional methods to.
Please note that all Seq
's are sequential and ordered streams, so don't bother to call parallel()
on it, it will
return the same Seq
.
Seq
adds a handful of useful methods, such as:
// (1, 2, 3, 4, 5, 6)
Seq.of(1, 2, 3).concat(Seq.of(4, 5, 6));
// true
Seq.of(1, 2, 3, 4).contains(2);
// true
Seq.of(1, 2, 3, 4).containsAll(2, 3);
// true
Seq.of(1, 2, 3, 4).containsAny(2, 5);
// (tuple(1, "A"), tuple(1, "B"), tuple(2, "A"), tuple(2, "B"))
Seq.of(1, 2).crossJoin(Seq.of("A", "B"));
// (1, 2, 3, 1, 2, 3, 1, 2, 3, 1, 2, ...)
Seq.of(1, 2, 3).cycle();
// tuple((1, 2, 3), (1, 2, 3))
Seq.of(1, 2, 3).duplicate();
// "abc"
Seq.of("a", "b", "c").foldLeft("", (u, t) -> t + u);
// "cba"
Seq.of("a", "b", "c").foldRight("", (t, u) -> t + u);
// { 1 = (1, 3), 0 = (2, 4) }
Seq.of(1, 2, 3, 4).groupBy(i -> i % 2);
// (tuple(1, (1, 3)), tuple(0, (2, 4)))
Seq.of(1, 2, 3, 4).grouped(i -> i % 2);
// (tuple(1, 1), tuple(2, 2))
Seq.of(1, 2, 4).innerJoin(Seq.of(1, 2, 3), (a, b) -> a == b);
// (1, 0, 2, 0, 3, 0, 4)
Seq.of(1, 2, 3, 4).intersperse(0);
// "123"
Seq.of(1, 2, 3).join();
// "1, 2, 3"
Seq.of(1, 2, 3).join(", ");
// "^1|2|3$"
Seq.of(1, 2, 3).join("|", "^", "$");
// (tuple(1, 1), tuple(2, 2), tuple(4, null))
Seq.of(1, 2, 4).leftOuterJoin(Seq.of(1, 2, 3), (a, b) -> a == b);
// (1, 2)
Seq.of(1, 2, 3, 4, 5).limitWhile(i -> i < 3);
// (1, 2)
Seq.of(1, 2, 3, 4, 5).limitUntil(i -> i == 3);
// (1, 2L)
Seq.of(new Object(), 1, "B", 2L).ofType(Number.class);
// (tuple(1, 1), tuple(2, 2), tuple(null, 3))
Seq.of(1, 2, 4).rightOuterJoin(Seq.of(1, 2, 3), (a, b) -> a == b);
// tuple((1, 3), (2, 4))
Seq.of(1, 2, 3, 4).partition(i -> i % 2 != 0);
// (1, 3, 4)
Seq.of(1, 2, 3, 4).remove(2);
// (1, 4)
Seq.of(1, 2, 3, 4).removeAll(2, 3, 5);
// (2, 3)
Seq.of(1, 2, 3, 4).retainAll(2, 3, 5);
// (4, 3, 2, 1)
Seq.of(1, 2, 3, 4).reverse();
// (3, 1, 4, 5, 2) for example
Seq.of(1, 2, 3, 4, 5).shuffle();
// (3, 4, 5)
Seq.of(1, 2, 3, 4, 5).skipWhile(i -> i < 3);
// (3, 4, 5)
Seq.of(1, 2, 3, 4, 5).skipUntil(i -> i == 3);
// (2, 3)
Seq.of(1, 2, 3, 4, 5).slice(1, 3)
// tuple((1, 2), (3, 4, 5))
Seq.of(1, 2, 3, 4, 5).splitAt(2);
// tuple(1, (2, 3, 4, 5))
Seq.of(1, 2, 3, 4, 5).splitAtHead();
// tuple((1, 2, 3), (a, b, c))
Seq.unzip(Seq.of(tuple(1, "a"), tuple(2, "b"), tuple(3, "c")));
// (tuple(1, "a"), tuple(2, "b"), tuple(3, "c"))
Seq.of(1, 2, 3).zip(Seq.of("a", "b", "c"));
// ("1:a", "2:b", "3:c")
Seq.of(1, 2, 3).zip(Seq.of("a", "b", "c"), (x, y) -> x + ":" + y);
// (tuple("a", 0), tuple("b", 1), tuple("c", 2))
Seq.of("a", "b", "c").zipWithIndex();
Lambda expressions and checked exceptions are a major pain. Even before going live with Java 8, there are a lot of Stack Overflow questions related to the subject:
- http://stackoverflow.com/q/18198176/521799
- http://stackoverflow.com/q/19757300/521799
- http://stackoverflow.com/q/14039995/521799
The Unchecked class can be used to wrap common @FunctionalInterfaces
in equivalent ones that are allowed to throw checked exceptions. E.g. this painful beast:
Arrays.stream(dir.listFiles()).forEach(file -> {
try {
System.out.println(file.getCanonicalPath());
}
catch (IOException e) {
throw new RuntimeException(e);
}
// Ouch, my fingers hurt! All this typing!
});
... will become this beauty:
Arrays.stream(dir.listFiles()).forEach(
Unchecked.consumer(file -> { System.out.println(file.getCanonicalPath()); })
);
<dependency>
<groupId>org.jooq</groupId>
<artifactId>jool</artifactId>
<version>0.9.10</version>
</dependency>