Happy Holidays!

It’s time for some Java Reindeer games.

A Festival of lights in New York

This blog is going to be mostly code. I am going to demonstrate some Eclipse Collections and Java Stream APIs, with a holiday twist. I’ll start by implementing a Reindeer Enum in Java with some help from .

public enum Reindeer
{
    Dasher, Dancer, Prancer, Vixen, Comet, Cupid, Donner, Blitzen,
    Rudolph;

    public static ImmutableList<Reindeer> all()
    {
        return theMostFamousReindeerOfAll()
                .newWithAll(theOtherReindeer()
                        .flatCollect(Reindeer::toList));
    }

    private static ImmutableList<Twin<Reindeer>> theOtherReindeer()
    {
        return Lists.immutable.with(
                Dasher.and(Dancer),
                Prancer.and(Vixen),
                Comet.and(Cupid),
                Donner.and(Blitzen));
    }

    private static ImmutableList<Reindeer> theMostFamousReindeerOfAll()
    {
        return Lists.immutable.with(Reindeer.Rudolph);
    }

    private static ImmutableList<Reindeer> toList(Twin<Reindeer> twin)
    {
        return Lists.immutable.with(twin.getOne(), twin.getTwo());
    }

    public Twin<Reindeer> and(Reindeer other)
    {
        return Tuples.twin(this, other);
    }

    public int nameLength()
    {
        return this.name().length();
    }

    public Character firstLetterOfName()
    {
        return Character.valueOf(this.name().charAt(0));
    }
}

First, I create an of Reindeer with Rudolph at the front in the method named all. I create an ImmutableList of pairs of all of the other reindeer, based on their usual order in the popular song. I use the type , which is a that has the same type for both items. Finally, I used the method to flatten all of the pairs of Reindeer into a single list which is appended to the ImmutableList with Rudolph using the method.

Now I will implement some tests for the Reindeer name games.

/**
 * Create a comma separated String of the Reindeer names.
 */
@Test
public void reindeerNameGame1()
{
    String expectedNames = "Rudolph, " +
            "Dasher, Dancer, " +
            "Prancer, Vixen, " +
            "Comet, Cupid, " +
            "Donner, Blitzen";

    Assert.assertEquals(
            expectedNames,
            Reindeer.all().makeString(", "));

    Assert.assertEquals(
            expectedNames,
            String.join(", ",
                    Reindeer.all()
                            .asLazy()
                            .collect(Reindeer::name)));

    Assert.assertEquals(
            expectedNames,
            Reindeer.all()
                    .stream()
                    .map(Reindeer::name)
                    .collect(Collectors.joining(", ")));
}

In this test, I show three different ways a comma separated String of the reindeer names can be created. First, I use from Eclipse Collections. The method does not require the object to be a CharSequence. It uses the toString implementation of the Object.

Next, I use which was added in Java 8. This method takes an Iterable of CharSequence, which I create using a with .

Finally, I use a with the ImmutableList returned from all and then map each Reindeer to its name, and collect them all into a String using Collectors.joining. All three approaches have the exact same result.

/**
 * Count the Reindeer names based on their size.
 */
@Test
public void reindeerNameGame2()
{
    IntBag nameCounts =
            Reindeer.all()
                    .asLazy()
                    .collectInt(Reindeer::nameLength).toBag();

    IntBag nameCountsFromIntStream =
            IntBags.mutable.withAll(
                    Reindeer.all()
                            .stream()
                            .mapToInt(Reindeer::nameLength));

    Assert.assertEquals(nameCounts, nameCountsFromIntStream);
    Assert.assertEquals(3, nameCounts.occurrencesOf(5));
    Assert.assertEquals(3, nameCounts.occurrencesOf(6));
    Assert.assertEquals(3, nameCounts.occurrencesOf(7));

    Bag<Integer> nameCountsBy =
            Reindeer.all().countBy(Reindeer::nameLength);

    Assert.assertEquals(3, nameCountsBy.occurrencesOf(5));
    Assert.assertEquals(3, nameCountsBy.occurrencesOf(6));
    Assert.assertEquals(3, nameCountsBy.occurrencesOf(7));

    Map<Integer, Long> streamNameCounts =
            Reindeer.all()
                    .stream()
                    .collect(Collectors.groupingBy(
                            Reindeer::nameLength,
                            Collectors.counting()));

    Assert.assertEquals(new Long(3), streamNameCounts.get(5));
    Assert.assertEquals(new Long(3), streamNameCounts.get(6));
    Assert.assertEquals(new Long(3), streamNameCounts.get(7));
}

In this test, I show four different ways to count the names of the Reindeer by their length. First, I create an , by collecting all of the name lengths for the Reindeer using and then converting the result .

In the second case, I create an IntStream from the Reindeer by mapping their name lengths to an int using mapToInt. I use the method to create an IntBag from an IntStream.

This method became available in Eclipse Collections 9.0 (Look at Item #3 for a comparison to previous versions). The third solution is the simplest. I use the method which is available on types that extend in Eclipse Collections.

Finally, I use Stream with Collectors.groupingBy and which results in a Map of Integer to Long.

/**
 * Group Reindeer by the first letter of their names.
 */
@Test
public void reindeerNameGame3()
{
    Multimap<Character, Reindeer> multimap =
            Reindeer.all().groupBy(Reindeer::firstLetterOfName);

    Map<Character, List<Reindeer>> mapOfLists =
            Reindeer.all()
                    .stream()
                    .collect(Collectors.groupingBy(
                            Reindeer::firstLetterOfName));

    Assert.assertEquals("Dasher, Dancer, Donner",
            multimap.get('D').makeString(", "));
    Assert.assertEquals("Comet, Cupid",
            multimap.get('C').makeString(", "));
    Assert.assertEquals(multimap.get('D'), mapOfLists.get('D'));
    Assert.assertEquals(multimap.get('C'), mapOfLists.get('C'));
}

In this test, I illustrate two ways to group Reindeer by the first letter of their last name. First, I use the method available directly on ImmutableList, which returns a .

In the second example, I use the stream method on and collect method on Stream with the groupingBy Collector on the utility class.

I hope you enjoyed joining in these reindeer games. I explored a bunch of and APIs in these three examples that may be useful in your own Java code.

Have a Happy Holiday and Happy New Year!

is open for . If you like the library, you can let us know by starring it on GitHub.