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danielso2007danielso2007
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feat: Java 8 – Convert List to Map.
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Lines changed: 199 additions & 4 deletions

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‎src/main/java/br/com/somejava8examples/commons/entities/Hosting.java‎

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package br.com.somejava8examples.commons.entities;
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import java.util.Objects;
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public class Hosting {
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private int Id;
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private String name;
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private long websites;
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public Hosting(int id, String name, long websites) {
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Id = id;
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this.name = name;
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this.websites = websites;
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}
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public int getId() {
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return Id;
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}
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public void setId(int id) {
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Id = id;
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}
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public String getName() {
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return name;
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}
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public void setName(String name) {
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this.name = name;
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}
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public long getWebsites() {
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return websites;
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}
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public void setWebsites(long websites) {
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this.websites = websites;
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}
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@Override
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public boolean equals(Object o) {
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if (this == o) return true;
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if (!(o instanceof Hosting)) return false;
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Hosting hosting = (Hosting) o;
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return getId() == hosting.getId() &&
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getWebsites() == hosting.getWebsites() &&
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Objects.equals(getName(), hosting.getName());
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}
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@Override
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public int hashCode() {
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return Objects.hash(getId(), getName(), getWebsites());
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}
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@Override
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public String toString() {
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return "Hosting{" +
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"Id=" + Id +
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", name='" + name + '\'' +
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", websites=" + websites +
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'}';
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}
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}

‎src/main/java/br/com/somejava8examples/map/ConvertListToMapService.java‎

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package br.com.somejava8examples.map;
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import br.com.somejava8examples.commons.entities.Hosting;
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import org.springframework.stereotype.Service;
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import java.util.*;
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import java.util.stream.Collectors;
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@Service
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public class ConvertListToMapService {
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private List<Hosting> getList() {
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List<Hosting> list = new ArrayList<>();
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list.add(new Hosting(1, "liquidweb.com", 80000));
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list.add(new Hosting(2, "linode.com", 90000));
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list.add(new Hosting(3, "digitalocean.com", 120000));
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list.add(new Hosting(4, "aws.amazon.com", 200000));
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list.add(new Hosting(5, "google.com", 1));
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return list;
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}
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public Map<Integer, String> listToMapCollectorsToMap() {
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List<Hosting> list = getList();
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// key = id, value - websites
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Map<Integer, String> result1 = list.stream().collect(Collectors.toMap(Hosting::getId, Hosting::getName));
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System.out.println("Result 1 : " + result1);
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// key = name, value - websites
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Map<String, Long> result2 = list.stream().collect(Collectors.toMap(Hosting::getName, Hosting::getWebsites));
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System.out.println("Result 2 : " + result2);
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// Same with result1, just different syntax
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// key = id, value = name
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Map<Integer, String> result3 = list.stream().collect(Collectors.toMap(x -> x.getId(), x -> x.getName()));
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System.out.println("Result 3 : " + result3);
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return result3;
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}
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public Map<String, Long> listToMapDuplicatedKeyDuplicated() {
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List<Hosting> list = getList();
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list.add(new Hosting(6, "linode.com", 100000)); // new line
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// key = name, value - websites , but the key 'linode' is duplicated!?
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Map<String, Long> result1 = list.stream().collect(Collectors.toMap(Hosting::getName, Hosting::getWebsites));
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System.out.println("Result 1 : " + result1);
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return result1;
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}
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public Map<String, Long> listToMapDuplicatedKeyMerge() {
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List<Hosting> list = getList();
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list.add(new Hosting(6, "linode.com", 100000)); // new line
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Map<String, Long> result1 = list.stream().collect(
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Collectors.toMap(Hosting::getName, Hosting::getWebsites,
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(oldValue, newValue) -> oldValue
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)
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);
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System.out.println("Result 1 : " + result1);
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return result1;
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}
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public Map listToMapSortCollect() {
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List<Hosting> list = getList();
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list.add(new Hosting(6, "linode.com", 100000));
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//example 1
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Map result1 = list.stream()
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.sorted(Comparator.comparingLong(Hosting::getWebsites).reversed())
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.collect(
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Collectors.toMap(
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Hosting::getName, Hosting::getWebsites, // key = name, value = websites
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(oldValue, newValue) -> oldValue, // se a mesma chave, pegue a chave antiga
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LinkedHashMap::new // returns a LinkedHashMap, keep order
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));
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System.out.println("Result 1 : " + result1);
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return result1;
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}
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}

‎src/test/java/br/com/somejava8examples/map/ConvertListToMapTest.java‎

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package br.com.somejava8examples.map;
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import org.junit.jupiter.api.Test;
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import org.springframework.beans.factory.annotation.Autowired;
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import org.springframework.boot.test.context.SpringBootTest;
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import org.springframework.test.context.ActiveProfiles;
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import static org.junit.jupiter.api.Assertions.*;
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@SpringBootTest
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@ActiveProfiles("test")
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public class ConvertListToMapTest {
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@Autowired
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private ConvertListToMapService service;
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@Test
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public void listToMapCollectorsToMapTest() {
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assertFalse(service.listToMapCollectorsToMap().isEmpty(), "List is empty");
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}
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@Test
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public void listToMapDuplicatedKeyDuplicatedTest() {
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Exception exception = assertThrows(IllegalStateException.class, () -> {service.listToMapDuplicatedKeyDuplicated();});
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String expectedMessage = "Duplicate key linode.com (attempted merging values 90000 and 100000)";
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String actualMessage = exception.getMessage();
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assertEquals(actualMessage, expectedMessage);
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}
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@Test
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public void listToMapDuplicatedKeyMergeTest() {
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assertFalse(service.listToMapDuplicatedKeyMerge().isEmpty(), "List is empty");
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}
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@Test
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public void listToMapSortCollectTest() {
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assertFalse(service.listToMapSortCollect().isEmpty(), "List is empty");
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}
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}

‎src/test/java/br/com/somejava8examples/stream/StreamHasAlreadyBeenOperatedUponOrClosedTest.java‎

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private StreamHasAlreadyBeenOperatedUponOrClosedService service;
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@Test
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@DisplayName("Test Spring @Autowired Integration")
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public void streamIsClosedTest() {
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Exception exception = assertThrows(IllegalStateException.class, () -> {
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service.streamIsClosed();
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});
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Exception exception = assertThrows(IllegalStateException.class, () -> {service.streamIsClosed();});
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String expectedMessage = "stream has already been operated upon or closed";
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String actualMessage = exception.getMessage();

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