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streams HW #55

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6f37f76
part 1 hw and CollectorsExercise1
mmgeorg Apr 11, 2017
009e185
LambdaExercise
mmgeorg Apr 11, 2017
3c4547f
CollectorsExercise2 start
mmgeorg Apr 13, 2017
29f328d
CollectorsExercise2 fix + test
mmgeorg Apr 13, 2017
68100a6
Fixed remarks
mmgeorg Apr 13, 2017
5f8147d
part 3 StreamExercise
mmgeorg Apr 13, 2017
d6ca595
part 3 CollectorCombination
mmgeorg Apr 13, 2017
bb5a87e
deleted BinaryOperator in toMap realisation
mmgeorg Apr 14, 2017
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7 changes: 5 additions & 2 deletions src/main/java/data/Generator.java
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Original file line number Diff line number Diff line change
Expand Up @@ -60,7 +60,10 @@ public static Employee generateEmployee() {
}

public static List<Employee> generateEmployeeList() {
// TODO
throw new UnsupportedOperationException();
int maxLength = 10;
final int length = ThreadLocalRandom.current().nextInt(maxLength) + 1;
return Stream.generate(Generator::generateEmployee)
.limit(length)
.collect(toList());
}
}
70 changes: 51 additions & 19 deletions src/test/java/part1/exercise/StreamsExercise1.java
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Original file line number Diff line number Diff line change
Expand Up @@ -5,16 +5,12 @@
import data.Person;
import org.junit.Test;

import java.util.*;
import java.util.concurrent.ThreadLocalRandom;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.Stream;
import java.util.ArrayList;
import java.util.List;

import static data.Generator.generateEmployeeList;
import static java.util.stream.Collectors.groupingBy;
import static java.util.stream.Collectors.mapping;
import static java.util.stream.Collectors.toList;
import static org.junit.Assert.assertEquals;

public class StreamsExercise1 {
// https://youtu.be/kxgo7Y4cdA8 Сергей Куксенко и Алексей Шипилёв — Через тернии к лямбдам, часть 1
Expand All @@ -25,20 +21,56 @@ public class StreamsExercise1 {

@Test
public void getAllEpamEmployees() {
List<Person> epamEmployees = null;// TODO all persons with experience in epam
throw new UnsupportedOperationException();
final List<Employee> employees = generateEmployeeList();

List<Person> expected = new ArrayList<>();

for (Employee e : employees) {
for (JobHistoryEntry j : e.getJobHistory()) {
if (j.getEmployer().equals("epam")) {
expected.add(e.getPerson());
break;
}
}
}
List<Person> actual = employees.stream()
.filter(e -> e.getJobHistory().stream()
.map(JobHistoryEntry::getEmployer)
.anyMatch("epam"::equals))
.map(Employee::getPerson)
.collect(toList());

assertEquals(expected, actual);
}

@Test
public void getEmployeesStartedFromEpam() {
List<Person> epamEmployees = null;// TODO all persons with first experience in epam
throw new UnsupportedOperationException();
final List<Employee> employees = generateEmployeeList();

List<Person> expected = new ArrayList<>();

for (Employee e : employees) {
if (isFirstEmployerEpam(e))
expected.add(e.getPerson());
}
List<Person> actual = employees.stream()
.filter(StreamsExercise1::isFirstEmployerEpam)
.map(Employee::getPerson)
.collect(toList());

assertEquals(expected, actual);
}

private static boolean isFirstEmployerEpam(Employee e) {
return e.getJobHistory()
.stream()
.limit(1)
.anyMatch("epam"::equals);
}

@Test
public void sumEpamDurations() {
final List<Employee> employees = generateEmployeeList();

int expected = 0;

for (Employee e : employees) {
Expand All @@ -48,12 +80,12 @@ public void sumEpamDurations() {
}
}
}

// TODO
throw new UnsupportedOperationException();

// int result = ???
// assertEquals(expected, result);
int result = employees.stream()
.map(Employee::getJobHistory)
.flatMap(e -> e.stream()
.filter(h -> h.getEmployer().equals("epam")))
.mapToInt(JobHistoryEntry::getDuration)
.sum();
assertEquals(expected, result);
}

}
95 changes: 80 additions & 15 deletions src/test/java/part1/exercise/StreamsExercise2.java
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Original file line number Diff line number Diff line change
Expand Up @@ -5,15 +5,11 @@
import data.Person;
import org.junit.Test;

import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.stream.Stream;
import java.util.*;

import static data.Generator.generateEmployeeList;
import static java.util.stream.Collectors.*;
import static org.junit.Assert.assertEquals;
import static org.hamcrest.core.IsEqual.equalTo;
import static org.junit.Assert.assertThat;

public class StreamsExercise2 {
// https://youtu.be/kxgo7Y4cdA8 Сергей Куксенко и Алексей Шипилёв — Через тернии к лямбдам, часть 1
Expand All @@ -22,25 +18,94 @@ public class StreamsExercise2 {
// https://youtu.be/O8oN4KSZEXE Сергей Куксенко — Stream API, часть 1
// https://youtu.be/i0Jr2l3jrDA Сергей Куксенко — Stream API, часть 2

// TODO class PersonEmployerPair
// TODO class PersonEmployerDuration
private static class PersonEmployerDuration
{
private Person person;
private String employer;
private Integer duration;

PersonEmployerDuration(Person p, String e) {
this(p,e,0);
}

PersonEmployerDuration(Person p, String e, Integer d) {
employer = e;
person = p;
duration = d;
}

Person getPerson() {
return person;
}

String getEmployer() {
return employer;
}

int getDuration() {
return duration;
}
}

@Test
public void employersStuffLists() {
Map<String, List<Person>> employersStuffLists = null;// TODO
throw new UnsupportedOperationException();
Map<String, List<Person>> employersStuffLists = getEmployees().stream()
.flatMap(e -> e.getJobHistory()
.stream()
.map(j -> new PersonEmployerDuration(
e.getPerson(),
j.getEmployer())))
.collect(groupingBy(
PersonEmployerDuration::getEmployer,
mapping(PersonEmployerDuration::getPerson, toList())));

assertThat(employersStuffLists.get("Microsoft"),
equalTo(Collections.singletonList(new Person("John", "White", 25))));
}

@Test
public void indexByFirstEmployer() {
Map<String, List<Person>> employeesIndex = null;// TODO
throw new UnsupportedOperationException();
Map<String, List<Person>> employeesIndex = getEmployees().stream()
.map(e -> new PersonEmployerDuration(
e.getPerson(),
e.getJobHistory().get(0).getEmployer()))
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@senia-psm senia-psm Apr 12, 2017

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Avoid get.

.collect(groupingBy(PersonEmployerDuration::getEmployer,
mapping(PersonEmployerDuration::getPerson, toList())));

assertThat(employeesIndex.get("abc"), equalTo(null));
assertThat(employeesIndex.get("yandex"), equalTo(Arrays.asList(
new Person("John", "Doe", 21),
new Person("John", "Doe", 24),
new Person("Bob", "Doe", 27),
new Person("John", "Doe", 30))));
}

private static Map<String, Integer> jobHistory(List<JobHistoryEntry> jobHistory){
return jobHistory.stream()
.collect(groupingBy(
JobHistoryEntry::getEmployer,
summingInt(JobHistoryEntry::getDuration)));
}

@Test
public void greatestExperiencePerEmployer() {
Map<String, Person> employeesIndex = null;// TODO
Map<String, Person> employeesIndex = getEmployees().stream()
.flatMap(e -> jobHistory(e.getJobHistory())
.entrySet().stream()
.map(j -> new PersonEmployerDuration(
e.getPerson(),
j.getKey(),
j.getValue()))
)
.collect(groupingBy(
PersonEmployerDuration::getEmployer,
collectingAndThen(maxBy(Comparator.comparingInt(PersonEmployerDuration::getDuration)),
p->p.get().getPerson()))
);


assertEquals(new Person("John", "White", 28), employeesIndex.get("epam"));
assertThat(new Person("John", "White", 28), equalTo(employeesIndex.get("epam")));
}


Expand Down Expand Up @@ -80,7 +145,7 @@ private List<Employee> getEmployees() {
new Employee(
new Person("John", "White", 25),
Collections.singletonList(
new JobHistoryEntry(6, "QA", "epam")
new JobHistoryEntry(6, "QA", "Microsoft")
)),
new Employee(
new Person("John", "Galt", 26),
Expand Down
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