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feat: Java 8 Streams map() examples.
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‎src/main/java/br/com/somejava8examples/commons/entities/Staff.java

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package br.com.somejava8examples.commons.entities;
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import java.math.BigDecimal;
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import java.util.Objects;
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import br.com.somejava8examples.commons.BaseEntity;
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public class Staff implements BaseEntity {
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private String name;
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private int age;
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private BigDecimal salary;
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public Staff(String name, int age, BigDecimal salary) {
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this.name = name;
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this.age = age;
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this.salary = salary;
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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 int getAge() {
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return age;
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}
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public void setAge(int age) {
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this.age = age;
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}
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public BigDecimal getSalary() {
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return salary;
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}
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public void setSalary(BigDecimal salary) {
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this.salary = salary;
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}
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@Override
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public int hashCode() {
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return Objects.hash(age, name, salary);
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}
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@Override
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public boolean equals(Object obj) {
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if (this == obj) {
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return true;
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}
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if (!(obj instanceof Staff)) {
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return false;
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}
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Staff other = (Staff) obj;
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return age == other.age && Objects.equals(name, other.name) && Objects.equals(salary, other.salary);
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}
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@Override
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public String toString() {
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return "Staff [" + (name != null ? "name=" + name + ", " : "") + "age=" + age + ", "
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+ (salary != null ? "salary=" + salary : "") + "]";
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}
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}

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

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package br.com.somejava8examples.commons.entities;
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import java.util.Objects;
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import br.com.somejava8examples.commons.BaseEntity;
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public class StaffPublic implements BaseEntity {
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private String name;
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private int age;
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private String extra;
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public StaffPublic() {
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}
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public StaffPublic(String name, int age, String extra) {
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this.name = name;
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this.age = age;
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this.extra = extra;
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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 int getAge() {
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return age;
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}
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public void setAge(int age) {
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this.age = age;
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}
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public String getExtra() {
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return extra;
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}
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public void setExtra(String extra) {
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this.extra = extra;
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}
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@Override
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public int hashCode() {
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return Objects.hash(age, extra, name);
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}
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@Override
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public boolean equals(Object obj) {
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if (this == obj) {
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return true;
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}
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if (!(obj instanceof StaffPublic)) {
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return false;
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}
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StaffPublic other = (StaffPublic) obj;
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return age == other.age && Objects.equals(extra, other.extra) && Objects.equals(name, other.name);
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}
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@Override
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public String toString() {
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return "StaffPublic [" + (name != null ? "name=" + name + ", " : "") + "age=" + age + ", "
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+ (extra != null ? "extra=" + extra : "") + "]";
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}
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}

‎src/main/java/br/com/somejava8examples/streams/StreamsFilterMapService.java

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package br.com.somejava8examples.streams;
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import java.math.BigDecimal;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.List;
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import java.util.stream.Collectors;
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import org.springframework.stereotype.Service;
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import br.com.somejava8examples.commons.entities.Staff;
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import br.com.somejava8examples.commons.entities.StaffPublic;
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@Service
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public class StreamsFilterMapService {
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public static final String DANIEL = "daniel";
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public static final String JACK = "jack";
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public static final String LAWRENCE = "lawrence";
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public List<Integer> listOfStringsToUppercase() {
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List<String> alpha = Arrays.asList("a", "b", "c", "d");
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// Before Java8
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List<String> alphaUpper = new ArrayList<>();
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for (String s : alpha) {
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alphaUpper.add(s.toUpperCase());
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}
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System.out.println(alpha); // [a, b, c, d]
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System.out.println(alphaUpper); // [A, B, C, D]
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// Java 8
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List<String> collect = alpha.stream().map(String::toUpperCase).collect(Collectors.toList());
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System.out.println(collect); // [A, B, C, D]
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// Extra, streams apply to any data type.
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List<Integer> num = Arrays.asList(1, 2, 3, 4, 5);
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List<Integer> collect1 = num.stream().map(n -> n * 2).collect(Collectors.toList());
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System.out.println(collect1); // [2, 4, 6, 8, 10]
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return collect1;
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}
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public List<String> listOfObjectsListOfString() {
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List<Staff> staff = Arrays.asList(new Staff(DANIEL, 30, new BigDecimal(10000)),
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new Staff(JACK, 27, new BigDecimal(20000)), new Staff(LAWRENCE, 33, new BigDecimal(30000)));
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// Before Java 8
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List<String> result = new ArrayList<>();
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for (Staff x : staff) {
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result.add(x.getName());
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}
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System.out.println(result); // [daniel, jack, lawrence]
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// Java 8
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List<String> collect = staff.stream().map(x -> x.getName()).collect(Collectors.toList());
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System.out.println(collect); // [daniel, jack, lawrence]
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return collect;
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}
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public List<StaffPublic> listOfObjectsListOfOtherObjects() {
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List<Staff> staff = Arrays.asList(new Staff(DANIEL, 30, new BigDecimal(10000)),
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new Staff(JACK, 27, new BigDecimal(20000)), new Staff(LAWRENCE, 33, new BigDecimal(30000)));
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List<StaffPublic> result = convertToStaffPublic(staff);
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System.out.println(result);
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return result;
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}
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private List<StaffPublic> convertToStaffPublic(List<Staff> staff) {
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List<StaffPublic> result = new ArrayList<>();
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for (Staff temp : staff) {
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StaffPublic obj = new StaffPublic();
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obj.setName(temp.getName());
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obj.setAge(temp.getAge());
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if (DANIEL.equals(temp.getName())) {
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obj.setExtra("this field is for daniel only!");
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}
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result.add(obj);
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}
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return result;
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}
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public List<StaffPublic> convertInsideTheMapMethodDirectly() {
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List<Staff> staff = Arrays.asList(new Staff(DANIEL, 30, new BigDecimal(10000)),
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new Staff(JACK, 27, new BigDecimal(20000)), new Staff(LAWRENCE, 33, new BigDecimal(30000)));
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// convert inside the map() method directly.
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List<StaffPublic> result = staff.stream().map(temp -> {
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StaffPublic obj = new StaffPublic();
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obj.setName(temp.getName());
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obj.setAge(temp.getAge());
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if (DANIEL.equals(temp.getName())) {
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obj.setExtra("this field is for daniel only!");
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}
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return obj;
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}).collect(Collectors.toList());
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System.out.println(result);
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return result;
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}
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}

‎src/test/java/br/com/somejava8examples/comparator/StreamsFilterMapsTest.java

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package br.com.somejava8examples.comparator;
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import static org.springframework.util.Assert.isTrue;
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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 br.com.somejava8examples.streams.StreamsFilterMapService;
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@SpringBootTest
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@ActiveProfiles("test")
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public class StreamsFilterMapsTest {
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@Autowired
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private StreamsFilterMapService service;
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@Test
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public void listOfStringsToUppercaseTest() {
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isTrue(!service.listOfStringsToUppercase().isEmpty(), "List is empty");
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}
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@Test
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public void listOfObjectsListOfStringTest() {
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isTrue(!service.listOfObjectsListOfString().isEmpty(), "List is empty");
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}
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@Test
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public void listOfObjectsListOfOtherObjectsTest() {
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isTrue(!service.listOfObjectsListOfOtherObjects().isEmpty(), "List is empty");
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}
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@Test
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public void convertInsideTheMapMethodDirectlyTest() {
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isTrue(!service.convertInsideTheMapMethodDirectly().isEmpty(), "List is empty");
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}
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}

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