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Diagram

Pet Kata

Learning through exercises

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Pet Kata domain

  • Domain objects are initialized in PetDomainForKata
  • Data is available to you through this.people

Diagram

Exercise 1

  • down: New concepts for Exercise 1
  • right: Exercise 1 solutions

Collect Pattern

  • Collect Pattern (a.k.a. map or transform).
  • Returns a new collection where each element has been transformed.
    • e.g. collect each pet's name.
  • Function is the type that takes an object and returns an object of a different type.
    • a.k.a. Transformer.

Collect Pattern (legacy for loop)

List<Pet> pets = someCodeToGetPets();
List<String> petNames = new ArrayList<>();
for (Pet pet : pets)
{
  petNames.add(pet.getName());
}

Collect Pattern

(Eclipse Collections)

MutableList<Pet> pets = someCodeToGetPets();

Lambda

MutableList<String> petNames = pets.collect(pet -> pet.getName());

Method Reference

MutableList<String> petNames = pets.collect(Pet::getName);

Select Pattern

  • Select Pattern (a.k.a. filter).
  • Returns the elements of collections that satisfy some condition.
    • e.g. select only those people who have a pet.
  • Predicate is the type that takes an object and returns a boolean.

Select Pattern (legacy for loop)

List<Person> people = someCodeToGetPeople();
List<Person> petPeople = new ArrayList<>();
for (Person person : people)
{
  if (person.isPetPerson())
  {
    petPeople.add(person);
  }
}

Select Pattern

(Eclipse Collections)

MutableList<Person> people = someCodeToGetPeople();

Lambda

MutableList<Person> petPeople = 
  people.select(person -> person.isPetPerson());

Method Reference

MutableList<Person> petPeople = people.select(Person::isPetPerson);

Exercise 1

  • Fix Exercise1Test; there are failing tests.
  • Figure out how to get the tests to pass using what you have seen so far.

Exercise 1 solutions

  • down: Exercise 1 solutions
  • right: Exercise 2

Get first names of people

@Test
public void getFirstNamesOfAllPeople()
{
  MutableList<String> firstNames =
    this.people.collect(Person::getFirstName);
  MutableList<String> expectedFirstNames =
    Lists.mutable.with("Mary", "Bob", "Ted", "Jake", "Barry", "Terry", "Harry", "John");
  Assert.assertEquals(expectedFirstNames, firstNames);
}

Get names of Mary Smith's Pets

@Test
public void getNamesOfMarySmithsPets()
{
  Person person = this.getPersonNamed("Mary Smith");
  MutableList<Pet> pets = person.getPets();
  MutableList<String> names =
    pets.collect(eachPet -> eachPet.getName());
  Assert.assertEquals("Tabby", names.makeString());
}

Get people with cats

@Test
public void getPeopleWithCats()
{
  MutableList<Person> people = this.people;
  MutableList<Person> peopleWithCats =
    people.select(person -> person.hasPet(PetType.CAT));
  Verify.assertSize(2, peopleWithCats);
}

Get people without cats

@Test
public void getPeopleWithoutCats()
{
  MutableList<Person> peopleWithoutCats =
    this.people.reject(person -> person.hasPet(PetType.CAT));
  Verify.assertSize(6, peopleWithoutCats);
}

Exercise 2

  • down: New concepts for Exercise 2
  • right: Exercise 2 solutions

TestUtils

  • Eclipse Collections distribution includes eclipse-collections-testutils.jar.
    • Includes helpful utility for writing unit tests.
    • Collection specific.
    • Implemented as an extention of JUnit.
    • Better error messages.
    • Most important class is called Verify.

TestUtils Code Example

Example from previous solution

Verify.assertSize(2, peopleWithCats);

Instead of

Assert.assertEquals(2, peopleWithCats.size());

Flat Collect Pattern

  • flatCollect() is a special case of collect()
  • With collect(), when the Function returns a collection, the result is collection of collections.

collect example

MutableList<Person> people = ...;
Function<Person, Iterable<PetType>> function =
  person -> person.getPetTypes();
MutableList<MutableList<PetType>> pets = people.collect(function);

Flat Collect Pattern

  • flatCollect() outputs a single flattened collection instead of a collection of collections.
  • The signature of flatCollect() is similar to collect(), except that the Function parameter must map to an Iterable type.

Method Signature

flatCollect(Function<? super T, ? extends Iterable<V>> function);

flatCollect example

MutableList<Person> people = ...;
MutableList<PetType> pets =
  people.flatCollect(person -> person.getPetTypes());

More Iteration Patterns

  • Patterns that use Predicate.
    • select returns the elements of a collection that satisfy the Predicate.
    • reject returns the elements of a collection that do not satisfy the Predicate.
    • count returns the number of elements that satisfy the Predicate.

More Iteration Patterns

  • Short-circuit pattern that use Predicate.
    • detect finds the first element that satisfies the Predicate.
    • anySatisfy returns true if any element satisfies the Predicate.
    • allSatisfy returns true if all elements satisfy the Predicate.
    • noneSatisfy returns true if no elements satisfy the Predicate.

Inheritance Hierarchy (List)

  • MutableList extends List
  • FastList is a drop-in replacement for ArrayList

Diagram

Inheritance Hierarchy (Set)

  • MutableSet extends Set
  • UnifiedSet is a drop-in replacement for HashSet

Diagram

With Methods

Review: How can we filter people over a certain age?

MutableList<Person> voters =
  people.select(person -> person.getAge() >= 18);

What if we want to find groups of people with different ages?

With Methods

  • collect(), select(), and reject() take a code block with a single parameter (Function and Predicate).
  • collectWith(), selectWith(), and rejectWith() are alternate forms that take two parameters.
    • A code block that takes two parameters.
    • An object that gets passed as the second argument to the code block.
  • Now the two-argument block is reusable.
Predicate2<Person, Integer> olderThan =
  (person, age) -> person.getAge() >= age;
MutableList<Person> drivers = people.selectWith(olderThan, 17);
MutableList<Person> voters = people.selectWith(olderThan, 18);
MutableList<Person> drinkers = people.selectWith(olderThan, 21);
MutableList<Person> sunsetRobotSquad = people.selectWith(olderThan, 160);

With Methods

  • Most iteration patterns have a corresponding "With" form.
    • collectWith()
    • selectWith()
    • detectWith()
    • anySatisfyWith()
    • ...etc

With Methods

  • These forms allow you to use method references in more situations.
MutableList<Person> peopleWithCatMethodReference =
  this.people.selectWith(Person::hasPet, PetType.CAT);
  • This is a made-up syntax with select() that does not compile. Only selectWith() allows us to use a method reference here.
// Does NOT compile
MutableList<Person> peopleWithCatsLambda =
  this.people.select(Person::hasPet(PetType.CAT));

Exercise 2

  • Fix Exercise2Test; they have failures.
  • Use the other iteration patterns that take a Predicate.
  • Use the flatCollect pattern.

Exercise 2 solutions

  • down: Exercise 2 solutions
  • right: Exercise 3

Do any people have cats

@Test
public void doAnyPeopleHaveCats()
{
  Predicate<Person> predicate = person -> person.hasPet(PetType.CAT);
  Assert.assertTrue(this.people.anySatisfy(predicate));
}

Do all people have pets

@Test
public void doAllPeopleHavePets()
{
  Predicate<Person> predicate = person -> person.isPetPerson();
  Assert.assertFalse(this.people.allSatisfy(predicate));
}

How many people have cats

@Test
public void howManyPeopleHaveCats()
{
  int count = this.people.count(person -> person.hasPet(PetType.CAT));
  Assert.assertEquals(2, count);
}

Find Mary Smith

@Test
public void findMarySmith()
{
  Person result = this.people.detectWith(Person::named, "Mary Smith");
  Assert.assertEquals("Mary", result.getFirstName());
  Assert.assertEquals("Smith", result.getLastName());
}

Get People With Pets

@Test
public void getPeopleWithPets()
{
  // Replace with only the pet owners.
  MutableList<Person> petPeople = this.people.select(person -> person.isPetPerson());
  Verify.assertSize(7, petPeople);
}

Get all pets of all people

@Test
public void getAllPetsOfAllPeople()
{
  Function<Person, Iterable<PetType>> function = person -> person.getPetTypes();
  MutableSet<PetType> petTypes = this.people.flatCollect(function, Sets.mutable.empty());
  Assert.assertEquals(
    Sets.mutable.with(PetType.CAT, PetType.DOG, PetType.TURTLE, PetType.HAMSTER, PetType.BIRD, PetType.SNAKE),
    petTypes);
}

Get first name of all people

@Test
public void getFirstNamesOfAllPeople()
{
  MutableList<String> firstNames = this.people.collect(Person::getFirstName);
  Assert.assertEquals(
    Lists.mutable.with("Mary", "Bob", "Ted", "Jake", "Barry", "Terry", "Harry", "John"),
    firstNames);
}

Do any people have cats (refactor)

@Test
public void doAnyPeopleHaveCatsRefactor()
{
  boolean peopleHaveCatsLambda = this.people.anySatisfy(person -> person.hasPet(PetType.CAT));
  Assert.assertTrue(peopleHaveCatsLambda);

  // Use a method reference, NOT a lambda, to solve the problem below.
  boolean peopleHaveCatsMethodRef = this.people.anySatisfyWith(Person::hasPet, PetType.CAT);
  Assert.assertTrue(peopleHaveCatsMethodRef);
}

Do all people have cats (refactor)

@Test
public void doAllPeopleHaveCatsRefactor()
{
  boolean peopleHaveCatsLambda = this.people.allSatisfy(person -> person.hasPet(PetType.CAT));
  Assert.assertFalse(peopleHaveCatsLambda);

  // Use a method reference, NOT a lambda, to solve the problem below.
  boolean peopleHaveCatsMethodRef = this.people.allSatisfyWith(Person::hasPet, PetType.CAT);
  Assert.assertFalse(peopleHaveCatsMethodRef);
}

Get people with cats (refactor)

@Test
public void getPeopleWithCatsRefator()
{
  // Use a method reference, NOT a lambda, to solve the problem below.
  MutableList<Person> peopleWithCatsMethodRef = this.people.selectWith(Person::hasPet, PetType.CAT);
  Verify.assertSize(2, peopleWithCatsMethodRef);
}

Get people without cats (refactor)

@Test
public void getPeopleWithoutCatsRefactor()
{
  // Use a method reference, NOT a lambda, to solve the problem below.
  MutableList<Person> peopleWithoutCatsMethodRef = this.people.rejectWith(Person::hasPet, PetType.CAT);
  Verify.assertSize(6, peopleWithoutCatsMethodRef);
}

Exercise 3

  • down: New concepts for Exercise 3
  • right: Exercise 3 solutions

Bag

Bag

  • Useful when you would otherwise use Map<K, Integer>
    • For example, to track the count of each PetType.
    • a.k.a. Multiset, Histogram
  • Using a Map, how should we fill in the blank?
MutableList<Person> people = ...;
MutableList<PetType> pets = people.flatCollect(Person::getPetTypes);
MutableMap<PetType, Integer> petTypeCounts = Maps.mutable.empty();
// ???
int cats = petTypeCounts.get(PetType.CAT);

Bag

MutableMap<PetType, Integer> petTypeCounts = Maps.mutable.empty();
for (PetType petType : pets)
{
  Integer count = petTypeCounts.get(petType);
  if (count == null)
  {
    count = 0;
  }
  petTypeCounts.put(petType, count + 1);
}
  • Lot of boilerplate code to handle uninitialized counts.

Bag

  • Bag is implemented as a map of key to count.
  • Like a List, but unordered.
  • Like a Set, but allows duplicates.
MutableBag<PetType> petTypeCounts = pets.toBag();
int cat = petTypeCounts.occurrencesOf(PetType.CAT);

Bag

Methods Inherited from
select(), collect(), etc. RichIterable
add(), remove(), iterator(), etc. MutableCollection (java.util.Collection)
occurencesOf(), forEachWithOccurences(), toMapOfItemToCount() Bag
addOccurences(), removeOccurences() MutableBag

Bag

MutableBag<String> bag =
  Bags.mutable.with("one", "two", "two", "three", "three", "three");

Assert.assertEquals(3, bag.occurrencesOf("three"));

bag.add("one");
Assert.assertEquals(2, bag.occurrencesOf("one"));

bag.addOccurrences("one", 4);
Assert.assertEquals(6, bag.occurrencesOf("one"));

Multimap

Multimap

  • Multimap is similar to Map, but associates a key to multiple values.
  • Useful when you would otherwise use Map<K, Collection<V>>
    • For example, group people with same last name.
MutableList<Person> people = ...;
MutableMap<String, MutableList<Person>> lastNamesToPeople =
  Maps.mutable.empty();
// ???
MutableList<Person> smiths = lastNamesToPeople.get("Smith");

Multimap

  • Code to populated the Map<K, Collection<V>>
  • Lot of boilerplate code to handle uninitialized backing collections.
MutableMap<String, MutableList<Person>> lastNamesToPeople =
  Maps.mutable.empty();

for (Person person : people)
{
  String lastName = person.getLastName();
  MutableList<Person> peopleWithLastName =
    lastNamesToPeople.get(lastName);

  if (peopleWithLastName == null)
  {
    peopleWithLastName = Lists.mutable.empty();
    lastNamesToPeople.put(lastName, peopleWithLastName);
  }
  peopleWithLastName.add(person);
}
MutableList<Person> smiths = lastNamesToPeople.get("Smith");

Multimap

  • Using Multimap for the same example
MutableListMultimap<String, Person> lastNamesToPeople =
  people.groupBy(Person::getLastName);

MutableList<Person> smiths = lastNamesToPeople.get("Smith");

Multimap

  • What happens if you add the same key and value twice?
  • It depends on which type of multimap.
MutableMultimap<String, Person> multimap = ...;
multimap.put("Smith", person);
multimap.put("Smith", person);
RichIterable<Person> smiths = multimap.get("Smith");

Verify.assertIterableSize(???, smiths);

Multimap

  • When the multimap is a ListMultimap, the groups of values are lists, which allow duplicates.
MutableListMultimap<String, Person> multimap =
  Multimaps.mutable.list.empty();
multimap.put("Smith", person);
multimap.put("Smith", person);
MutableList<Person> smiths = multimap.get("Smith");

Verify.assertIterableSize(2, smiths);

Multimap

  • When the multimap is a SetMultimap, the groups of values are sets, which don't allow duplicates.
MutableSetMultimap<String, Person> multimap =
  Multimaps.mutable.set.empty();
multimap.put("Smith", person);
multimap.put("Smith", person);
MutableSet<Person> smiths = multimap.get("Smith");

Verify.assertIterableSize(1, smiths);

Multimap

  • groupByEach() is a special case of groupBy().
  • Analogous to the difference between collect() and flatCollect().
  • Appropriate when the Function returns an Iterable.
  • The return type is the same as groupBy(): Multimap.
MutableListMultimap<String, Person> lastNamesToPeople =
  people.groupBy(Person::getLastName);

MutableListMultimap<PetType, Person> petsToPeople =
  people.groupByEach(person -> person.getPets().collect(Pet::getType);

Target Collections

Target Collections

  • Let's say we have 3 people: mrSmith, mrsSmith, mrJones.
  • The first two share the same address.
  • What will get printed by the following code?
MutableSet<Person> people =
  Sets.mutable.with(mrSmith, mrsSmith, mrJones);

int numAddresses =
  people.collect(Person::getAddress).size();

System.out.println(numAddresses);

Target Collections

  • select(), collect(), etc. are defined with covariant return types:
    • MutableCollection.collect() returns a MutableCollection.
    • MutableList.collect() returns a MutableList.
    • MutableSet.collect() returns a MutableSet.

Target Collections

  • Alternate forms take target collections.
  • These forms return the same instance passed in as the target.
MutableSet<Person> people =
  Sets.mutable.with(mrSmith, mrsSmith, mrJones);

MutableList<Address> targetList = Lists.mutable.empty();

int numAddresses =
  people.collect(Person::getAddress, targetList).size();

System.out.println(numAddresses);

Exercise 3

  • Fix Exercise3Test; they have failures.
  • Use Bag, Multimap.

Exercise 3 solutions

  • down: Exercise 3 solutions
  • right: Exercise 4

Get counts by pet type

@Test
public void getCountsByPetType()
{
  MutableBag<PetType> counts =
    this.people.flatCollect(Person::getPets).countBy(Pet::getType);

  Assert.assertEquals(2, counts.occurrencesOf(PetType.CAT));
  Assert.assertEquals(2, counts.occurrencesOf(PetType.DOG));
  Assert.assertEquals(2, counts.occurrencesOf(PetType.HAMSTER));
  Assert.assertEquals(1, counts.occurrencesOf(PetType.SNAKE));
  Assert.assertEquals(1, counts.occurrencesOf(PetType.TURTLE));
  Assert.assertEquals(1, counts.occurrencesOf(PetType.BIRD));
}

Get people by last name

@Test
public void getPeopleByLastName()
{
  MutableListMultimap<String, Person> lastNamesToPeople =
    this.people.groupBy(Person::getLastName);

  Verify.assertIterableSize(3, lastNamesToPeople.get("Smith"));
}

Get people by their pets

@Test
public void getPeopleByTheirPets()
{
  MutableSetMultimap<PetType, Person> peopleByPetType =
    this.people.groupByEach(
      person -> person.getPetTypes(),
	  Multimaps.mutable.set.empty());

  Verify.assertIterableSize(2, peopleByPetType.get(PetType.CAT));
  Verify.assertIterableSize(2, peopleByPetType.get(PetType.DOG));
  Verify.assertIterableSize(1, peopleByPetType.get(PetType.HAMSTER));
  Verify.assertIterableSize(1, peopleByPetType.get(PetType.TURTLE));
  Verify.assertIterableSize(1, peopleByPetType.get(PetType.BIRD));
  Verify.assertIterableSize(1, peopleByPetType.get(PetType.SNAKE));
}

Exercise 4

  • down: New concepts for Exercise 4
  • right: Exercise 4 solutions

Primitive Collections

Primitive Collections

  • Each data structure has an analogous primitive version.
  • All primitive types are supported.

Primitive Collections

All 8 primitive collection interfaces

Diagram

Primitive Collections

Diagram

Primitive Collections

  • Primitive collections have the same rich and fluent API as regular collections.

Code Example

MutableIntList intListOfAges = this.people
  .flatCollect(Person::getPets)
  .collectInt(Pet::getAge);

MutableIntList selection =
  intListOfAges.select(age -> age > 2);

MutableIntSet intSetOfAges = intListOfAges.toSet();

Exercise 4

  • Fix Exercise4Test; they have failures.
  • Refactor Java 8 streams to Eclipse Collections.

Exercise 4 solutions

  • down: Exercise 4 solutions
  • right: Exercise 5

Get age statistics of pets

@Test
public void getAgeStatisticsOfPets()
{
  // Try to use a MutableIntList here instead.
  // Hints: flatMap = flatCollect, map = collect, mapToInt = collectInt
  IntList agesLazy = this.people.asLazy()
    .flatCollect(Person::getPets)
    .collectInt(Pet::getAge)
    .toList();
  // Try to use an IntSet here instead.
  IntSet uniqueAges = agesLazy.toSet();
  // IntSummaryStatistics is a class in JDK 8 - Try and use it with MutableIntList.forEach().
  IntSummaryStatistics stats = new IntSummaryStatistics();
  agesLazy.forEach(stats::accept);
  // Is a Set<Integer> equal to an IntSet?
  // Hint: Try IntSets instead of Sets as the factory.
  Assert.assertEquals(IntHashSet.newSetWith(1, 2, 3, 4), uniqueAges);
  // Try to leverage min, max, sum, average from the Eclipse Collections Primitive API.
  Assert.assertEquals(stats.getMin(), agesLazy.min());
  Assert.assertEquals(stats.getMax(), agesLazy.max());
  Assert.assertEquals(stats.getSum(), agesLazy.sum());
  Assert.assertEquals(stats.getAverage(), agesLazy.average(), 0.0);
  Assert.assertEquals(stats.getCount(), agesLazy.size());
  // Hint: Match = Satisfy
  Assert.assertTrue(agesLazy.allSatisfy(IntPredicates.greaterThan(0)));
  Assert.assertTrue(agesLazy.allSatisfy(i -> i > 0));
  Assert.assertFalse(agesLazy.anySatisfy(i -> i == 0));
  Assert.assertTrue(agesLazy.noneSatisfy(i -> i < 0));
  Assert.assertEquals(2.0d, agesLazy.median(), 0.0);
}

Stream to EC refactor #1

@Test
public void streamsToECRefactor1()
{
  // Find Bob Smith.
  Person person = this.people.detect(each -> each.named("Bob Smith"));

  // Get Bob Smith's pets' names
  String names = person.getPets().collect(Pet::getName).makeString(" & ");

  Assert.assertEquals("Dolly & Spot", names);
}

Stream to EC refactor #2

@Test
public void streamsToECRefactor2()
{
  // Hint: Try to replace the Map<PetType, Long> with a Bag<PetType>.
  MutableBag<PetType> counts = this.people
    .asUnmodifiable()
    .flatCollect(Person::getPets)
    .countBy(Pet::getType);

  Assert.assertEquals(2, counts.occurrencesOf(PetType.CAT));
  Assert.assertEquals(2, counts.occurrencesOf(PetType.DOG));
  Assert.assertEquals(2, counts.occurrencesOf(PetType.HAMSTER));
  Assert.assertEquals(1, counts.occurrencesOf(PetType.SNAKE));
  Assert.assertEquals(1, counts.occurrencesOf(PetType.TURTLE));
  Assert.assertEquals(1, counts.occurrencesOf(PetType.BIRD));
}

Stream to EC refactor #3

@Test
public void streamsToECRefactor3()
{
  // Hint: The result of groupingBy/counting can almost always be replaced by a Bag.
  // Hint: Look for the API on Bag that might return the top 3 pet types.
  MutableList<ObjectIntPair<PetType>> favorites = this.people
    .asLazy()
    .flatCollect(Person::getPets)
    .countBy(Pet::getType)
    .topOccurrences(3);

  Verify.assertSize(3, favorites);
  Verify.assertContains(PrimitiveTuples.pair(PetType.CAT, 2), favorites);
  Verify.assertContains(PrimitiveTuples.pair(PetType.DOG, 2), favorites);
  Verify.assertContains(PrimitiveTuples.pair(PetType.HAMSTER, 2), favorites);
}

Exercise 5

  • Exercise 5 is extra-credit.
  • Use methods on RichIterable.
  • Go right: Learn Exercise 5 solutions

Partition pet and non pet people

@Test
public void partitionPetAndNonPetPeople()
{
  PartitionMutableList<Person> partitionMutableList = this.people.partition(eachPerson -> eachPerson.isPetPerson());
  Verify.assertSize(7, partitionMutableList.getSelected());
  Verify.assertSize(1, partitionMutableList.getRejected());
}

Get oldest pet

@Test
public void getOldestPet()
{
  Pet oldestPet = this.people.flatCollect(Person::getPets).maxBy(pet -> pet.getAge());
  Assert.assertEquals(PetType.DOG, oldestPet.getType());
  Assert.assertEquals(4, oldestPet.getAge());
}

Get average pet age

@Test
public void getAveragePetAge()
{
  double averagePetAge = this.people.flatCollect(Person::getPets).collectDouble(Pet::getAge).average();
  Assert.assertEquals(1.8888888888888888, averagePetAge, 0.00001);
}

Add pet ages to existing set

@Test
public void addPetAgesToExistingSet()
{
  // Hint: Use petAges as a target collection
  MutableIntSet petAges = IntSets.mutable.with(5);
  this.people.flatCollect(Person::getPets).collectInt(pet -> pet.getAge(), petAges);
  Assert.assertEquals(IntSets.mutable.with(1, 2, 3, 4, 5), petAges);
}

Refactor to Eclipse Collections

@Test
public void refactorToEclipseCollections()
{
  // Replace List and ArrayList with Eclipse Collections types.
  MutableList<Person> people = Lists.mutable.with(
    new Person("Mary", "Smith").addPet(PetType.CAT, "Tabby", 2),
    new Person("Bob", "Smith")
      .addPet(PetType.CAT, "Dolly", 3)
      .addPet(PetType.DOG, "Spot", 2),
    new Person("Ted", "Smith").addPet(PetType.DOG, "Spike", 4),
    new Person("Jake", "Snake").addPet(PetType.SNAKE, "Serpy", 1),
    new Person("Barry", "Bird").addPet(PetType.BIRD, "Tweety", 2),
    new Person("Terry", "Turtle").addPet(PetType.TURTLE, "Speedy", 1),
    new Person("Harry", "Hamster")
      .addPet(PetType.HAMSTER, "Fuzzy", 1)
      .addPet(PetType.HAMSTER, "Wuzzy", 1),
    new Person("John", "Doe"));

  // Replace Set and HashSet with Eclipse Collections types.
  MutableIntSet petAges = people.flatCollect(Person::getPets).collectInt(Pet::getAge).toSet();

  // Extra bonus - convert to a primitive collection.
  Assert.assertEquals(IntSets.mutable.with(1, 2, 3, 4), petAges);
}

Congratulations!

You have completed the Pet Kata!

Enjoy happy Java development with Eclipse Collections!