kbreidenbach / utils

Utility types to give Java 9 more Scala like functionality

utils

Some utilities to make Java 9 even more expressive. This will be updated with code examples in the near future

Try

Try is a java version of the Scala type.

ForComp

ForComp attempts to give Java a little of the power of for comprehension similar to that of Scala.

Obviously, without the language having for comprehension built in there must be some compromises, but the result of the for comprehension here is still a powerful tool for Java.

The test cases give some good examples of usage

An example of swapping a nest loop for for comp ( full example )

    private int nestedLoops() {
        int result = 0;

        for (int i = 0; i < 100; i ++) {
            for(int j = 0; j < 50; j++) {
                for(int k = 0; k < 20; k++) {
                    result += (i + j + k);
                }
            }
        }

        return result;
    }

    private int nestedForComp() {
         return forComp(stream(0, 99)).
                with(stream(0, 49)).
                with(stream(0, 19)).
                yieldFlat().mapToInt(i -> i).sum();
    }

Match

Match gives a similar pattern matching function to that of Scala's match. Match.match takes a subject to match on and then a number of Case types for the patterns.

Like Scala's match if no pattern matches then a MatchException will be thrown

The Case class takes a predicate and a function that will be called if matched.

There are three helper methods in the Match class to help create Case types: matchCase creates a Case based on the predicate and function supplied typeCase takes a Class and matched based on type comparison defaultCase only takes a function and is used as a fall through match

Also like Scala's match, order is important and the match function will complete on the first pattern matched

Some contrived examples ( full example )

        final MatchExample example = new MatchExample();
        final Try<String> tryOne = example.successString();
        final Try<String> tryTwo = example.failureString();

        boolean worked = match(tryOne,
                typeCase(Success.class, o -> true),
                typeCase(Failure.class, o -> false));

        if (!worked) throw new RuntimeException("Should have worked");

        worked = match(tryTwo,
                typeCase(Success.class, o -> true),
                typeCase(Failure.class, o -> false));

        if (worked) throw new RuntimeException("Shouldn't have worked");


        final int i = 28;

        final int result = match(i,
                matchCase(e -> e + 1 == 30, e -> 30),
                matchCase(e -> e / 4 == 7, e -> 7));

        if (result != 7) throw new RuntimeException("Should've been 7");

        final Double pi = 3.1415927;

        final String answer = match(pi,
                typeCase(Integer.class, j -> "Not today"),
                matchCase(j -> j == 3.1415927, j-> "Eureka!"));

        if (!answer.equals("Eureka!")) throw new RuntimeException("Sunk");