jOOλ - The Missing Parts in Java 8 jOOλ improves the JDK libraries in areas where the Expert Group's focus was elsewhere. It adds tuple support, function support, and a lot of additional functionality around sequential Streams. The JDK 8's main efforts (default methods, lambdas, and the Stream API) were focused around maintaining backwards compa…
Java

README.md

jOOλ

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:

org.jooq.lambda.function

Why only Function and BiFunction? We have also included support for Function1 through Function16.

org.jooq.lambda.tuple

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.

org.jooq.lambda.Seq

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) -> u + t);

// "abc!"
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();

org.jooq.lambda.Unchecked

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:

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()); })
);

Maven

<dependency>
    <groupId>org.jooq</groupId>
    <artifactId>jool</artifactId>
    <version>0.9.11</version>
</dependency>