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Streams Part 2 (by Narek Karapetian) #81

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191 changes: 175 additions & 16 deletions src/test/java/part2/exercise/CollectorsExercise1.java
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Original file line number Diff line number Diff line change
Expand Up @@ -6,25 +6,49 @@
import org.junit.Test;

import java.util.*;
import java.util.concurrent.ThreadLocalRandom;
import java.util.function.BiConsumer;
import java.util.function.BinaryOperator;
import java.util.function.Function;
import java.util.function.Supplier;
import java.util.stream.Collector;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;

import static java.util.stream.Collectors.toList;
import static java.util.stream.Collectors.*;
import static org.junit.Assert.assertEquals;

public class CollectorsExercise1 {

@Test
public void getTheCoolestOne() {
final Map<String, Person> coolestByPosition = getCoolestByPosition(getEmployees());
final Map<String, Person> coolestByPosition1 = getCoolestByPositionFirstOption(getEmployees());
final Map<String, Person> coolestByPosition2 = getCoolestByPositionSecondOption(getEmployees());
final Map<String, Person> coolestByPosition3 = getCoolestByPositionThirdOption(getEmployees());

coolestByPosition.forEach((position, person) -> System.out.println(position + " -> " + person));
Person qa1 = coolestByPosition1.get("QA");
Person qa2 = coolestByPosition2.get("QA");
Person qa3 = coolestByPosition3.get("QA");

assertEquals(qa1, qa2);
assertEquals(qa2, qa3);
assertEquals(qa1, qa3);

Person dev1 = coolestByPosition1.get("dev");
Person dev2 = coolestByPosition2.get("dev");
Person dev3 = coolestByPosition3.get("dev");

assertEquals(dev1, dev2);
assertEquals(dev2, dev3);
assertEquals(dev1, dev3);

Person ba1 = coolestByPosition1.get("BA");
Person ba2 = coolestByPosition2.get("BA");
Person ba3 = coolestByPosition3.get("BA");

assertEquals(ba1, ba2);
assertEquals(ba2, ba3);
assertEquals(ba1, ba3);

// coolestByPosition3.forEach((position, person) -> System.out.println(position + " -> " + person));
}

private static class PersonPositionDuration {
Expand Down Expand Up @@ -52,31 +76,166 @@ public int getDuration() {
}

// With the longest duration on single job
private Map<String, Person> getCoolestByPosition(List<Employee> employees) {
private Map<String, Person> getCoolestByPositionFirstOption(List<Employee> employees) {
final Stream<PersonPositionDuration> personPositionDurationStream =
getPersonPositionDurationStream(employees);

// First option
// Collectors.maxBy
// Collectors.collectingAndThen
// Collectors.groupingBy
return personPositionDurationStream
.collect(
groupingBy(
PersonPositionDuration::getPosition,
collectingAndThen(
maxBy(Comparator.comparingInt(PersonPositionDuration::getDuration)),
personPositionDuration -> personPositionDuration.get().getPerson()
)
)
);
}

private Map<String, Person> getCoolestByPositionSecondOption(List<Employee> employees) {
final Stream<PersonPositionDuration> personPositionDurationStream =
getPersonPositionDurationStream(employees);

// Second option
// Collectors.toMap
// iterate twice: stream...collect(...).stream()...
// TODO
throw new UnsupportedOperationException();

final Map<String, PersonPositionDuration> intermediate =
personPositionDurationStream
.collect(
toMap(
PersonPositionDuration::getPosition,
Function.identity(),
(o1, o2) -> o1.getDuration() > o2.getDuration() ? o1 : o2
)
);

return intermediate.entrySet()
.stream()
.collect(
toMap(
Map.Entry::getKey,
t -> t.getValue().getPerson())
);
}

private Map<String, Person> getCoolestByPositionThirdOption(List<Employee> employees) {
final Stream<PersonPositionDuration> personPositionDurationStream =
getPersonPositionDurationStream(employees);

// Third option
// new Collector ...
return personPositionDurationStream
.collect(new Collector<PersonPositionDuration,
Map<String, PersonPositionDuration>,
Map<String, Person>>() {

@Override
public Supplier<Map<String, PersonPositionDuration>> supplier() {
return HashMap::new;
}

@Override
public BiConsumer<Map<String, PersonPositionDuration>, PersonPositionDuration> accumulator() {
return (map, ppd) -> {
map.putIfAbsent(ppd.getPosition(), ppd);
PersonPositionDuration current = map.get(ppd.getPosition());
if (ppd.getDuration() > current.getDuration()) {
map.put(ppd.getPosition(), ppd);
}
};
}

@Override
public BinaryOperator<Map<String, PersonPositionDuration>> combiner() {
return (accumFirst, accumSecond) -> {
accumSecond.forEach(
(position, ppd) ->
accumFirst.merge(
position, ppd,
(ppd1, ppd2) ->
ppd1.getDuration() > ppd2.getDuration() ? ppd1 : ppd2
)
);
return accumFirst;
};
}

@Override
public Function<Map<String, PersonPositionDuration>, Map<String, Person>> finisher() {
return map ->
map.entrySet().stream()
.collect(
toMap(
o -> o.getKey(),
t -> t.getValue().getPerson()
)
);
}

@Override
public Set<Characteristics> characteristics() {
return Collections.emptySet();
}
}
);
}


@Test
public void getTheCoolestOne2() {
final Map<String, Person> coolestByPosition = getCoolestByPosition2(getEmployees());

coolestByPosition.forEach((position, person) -> System.out.println(position + " -> " + person));
final Person qa = coolestByPosition.get("QA");
assertEquals(new Person("Bob", "Doe", 27), qa);

final Person dev = coolestByPosition.get("dev");
assertEquals(new Person("John", "Galt", 26), dev);

final Person ba = coolestByPosition.get("BA");
assertEquals(new Person("John", "White", 28), ba);

// coolestByPosition.forEach((position, person) -> System.out.println(position + " -> " + person));
}

// With the longest sum duration on this position
// { John Doe, [{dev, google, 4}, {dev, epam, 4}] } предпочтительнее, чем { A B, [{dev, google, 6}, {QA, epam, 100}]}
private Map<String, Person> getCoolestByPosition2(List<Employee> employees) {
// TODO
throw new UnsupportedOperationException();
return getPersonPositionDurationStream(employees)
.collect(
groupingBy(PersonPositionDuration::getPosition,
collectingAndThen(
groupingBy(
PersonPositionDuration::getPerson,
summingInt(PersonPositionDuration::getDuration)
),
m -> m.entrySet().stream()
.sorted((o1, o2) -> Integer.compare(o2.getValue(), o1.getValue()))
.map(Map.Entry::getKey)
.findFirst()
.get()
)
)
);
}


private Stream<PersonPositionDuration> getPersonPositionDurationStream(List<Employee> employees) {
return employees.stream()
.flatMap(
e -> e.getJobHistory().stream()
.map(j ->
new PersonPositionDuration(
e.getPerson(),
j.getPosition(),
j.getDuration()
)
)
);
}

private List<Employee> getEmployees() {
Expand Down Expand Up @@ -115,19 +274,19 @@ private List<Employee> getEmployees() {
new Employee(
new Person("John", "White", 25),
Collections.singletonList(
new JobHistoryEntry(6, "QA", "epam")
new JobHistoryEntry(7, "QA", "epam")
)),
new Employee(
new Person("John", "Galt", 26),
Arrays.asList(
new JobHistoryEntry(3, "dev", "epam"),
new JobHistoryEntry(1, "dev", "google")
new JobHistoryEntry(4, "dev", "epam"),
new JobHistoryEntry(5, "dev", "google")
)),
new Employee(
new Person("Bob", "Doe", 27),
Arrays.asList(
new JobHistoryEntry(4, "QA", "yandex"),
new JobHistoryEntry(2, "QA", "epam"),
new JobHistoryEntry(4, "QA", "epam"),
new JobHistoryEntry(2, "dev", "abc")
)),
new Employee(
Expand Down
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