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‎README.md

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@@ -16,10 +16,10 @@ This repository contains the code examples from the book [Modern Java in Action]
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- Chapter 8. Collection API enhancements | [java](https://github.com/codejsha/modern-java-in-action/tree/main/src/main/java/com/example/demo/chapter08)([test](https://github.com/codejsha/modern-java-in-action/tree/main/src/main/test/com/example/demo/chapter08))
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- Chapter 9. Refactoring, testing, and debugging | [java](https://github.com/codejsha/modern-java-in-action/tree/main/src/main/java/com/example/demo/chapter09)([test](https://github.com/codejsha/modern-java-in-action/tree/main/src/main/test/com/example/demo/chapter09))
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- Chapter 10. Domain-specific languages using lambdas | [java](https://github.com/codejsha/modern-java-in-action/tree/main/src/main/java/com/example/demo/chapter10)([test](https://github.com/codejsha/modern-java-in-action/tree/main/src/main/test/com/example/demo/chapter10))
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- Chapter 11. Using Optional as a better alternative to null | [java](https://github.com/codejsha/modern-java-in-action/tree/main/src/main/java/com/example/demo/chapter11)([test](https://github.com/codejsha/modern-java-in-action/tree/main/src/main/test/com/example/demo/chapter11))
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(work in progress)
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- Chapter 11. Using Optional as a better alternative to null
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- Chapter 12. New Date and Time API
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- Chapter 13. Default methods
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- Chapter 14. The Java Module System

‎src/main/java/com/example/demo/chapter11/Car.java

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package com.example.demo.chapter11;
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import java.util.Optional;
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public record Car(Optional<Insurance> insurance) {
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}

‎src/main/java/com/example/demo/chapter11/CarInsuranceProcessing.java

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package com.example.demo.chapter11;
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import lombok.extern.slf4j.Slf4j;
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import java.util.List;
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import java.util.Optional;
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import java.util.Set;
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import java.util.stream.Collectors;
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@Slf4j
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public class CarInsuranceProcessing {
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@SuppressWarnings("OptionalUsedAsFieldOrParameterType")
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public static String getCarInsuranceName(Optional<Person> person) {
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return person.flatMap(Person::car)
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.flatMap(Car::insurance)
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.map(Insurance::name)
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.orElse("Unknown");
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}
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@SuppressWarnings("OptionalUsedAsFieldOrParameterType")
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public static String getCarInsuranceName(Optional<Person> person, int minAge) {
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return person.filter(p -> p.age() >= minAge)
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.flatMap(Person::car)
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.flatMap(Car::insurance)
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.map(Insurance::name)
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.orElse("Unknown");
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}
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public static Set<String> getCarInsuranceNames(List<Person> persons) {
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return persons.stream()
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.map(Person::car)
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.map(optCar -> optCar.flatMap(Car::insurance))
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.map(optInsurance -> optInsurance.map(Insurance::name))
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.flatMap(Optional::stream)
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.collect(Collectors.toSet());
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}
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@SuppressWarnings("OptionalUsedAsFieldOrParameterType")
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public static Optional<Insurance> nullSafeFindCheapestInsurance(Optional<Person> person, Optional<Car> car) {
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return person.flatMap(p -> car.map(c -> findCheapestInsurance(p, c)));
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// if (person.isPresent() && car.isPresent()) {
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// return Optional.of(findCheapestInsurance(person.get(), car.get()));
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// } else {
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// return Optional.empty();
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// }
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}
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public static Insurance findCheapestInsurance(Person person, Car car) {
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// dummy
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return car.insurance().orElse(new Insurance("Unknown"));
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}
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}

‎src/main/java/com/example/demo/chapter11/Insurance.java

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package com.example.demo.chapter11;
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public record Insurance(String name) {
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}

‎src/main/java/com/example/demo/chapter11/Person.java

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package com.example.demo.chapter11;
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import java.util.Optional;
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public record Person(Optional<Car> car, int age) {
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}

‎src/main/java/com/example/demo/chapter11/PropertyProcessing.java

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package com.example.demo.chapter11;
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import lombok.extern.slf4j.Slf4j;
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import java.util.Optional;
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import java.util.Properties;
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@Slf4j
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public class PropertyProcessing {
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public static int readDurationImperative(Properties props, String name) {
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String value = props.getProperty(name);
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if (value != null) {
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try {
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int i = Integer.parseInt(value);
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if (i > 0) {
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return i;
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}
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} catch (NumberFormatException e) {
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// e.printStackTrace();
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}
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}
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return 0;
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}
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public static int readDurationWithOptional(Properties props, String name) {
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return Optional.ofNullable(props.getProperty(name))
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.flatMap(PropertyProcessing::stringToOptionalInt)
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.filter(i -> i > 0)
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.orElse(0);
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}
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public static Optional<Integer> stringToOptionalInt(String str) {
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try {
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return Optional.of(Integer.parseInt(str));
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} catch (NumberFormatException e) {
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return Optional.empty();
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}
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}
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}

‎src/main/test/com/example/demo/chapter11/CarInsuranceProcessingTest.java

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package com.example.demo.chapter11;
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import lombok.extern.slf4j.Slf4j;
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import org.junit.jupiter.api.BeforeEach;
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import org.junit.jupiter.api.Test;
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import java.util.List;
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import java.util.Optional;
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import static org.junit.jupiter.api.Assertions.*;
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@Slf4j
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class CarInsuranceProcessingTest {
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private Insurance cambridgeInsurance;
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private Car car1;
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private Car car2;
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private Person person1;
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private Person person2;
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private Person person3;
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@BeforeEach
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void setUp() {
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cambridgeInsurance = new Insurance("CambridgeInsurance");
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car1 = new Car(Optional.of(cambridgeInsurance));
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car2 = new Car(Optional.empty());
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person1 = new Person(Optional.of(car1), 20);
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person2 = new Person(Optional.empty(), 25);
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person3 = new Person(Optional.of(car2), 30);
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}
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@Test
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void testGetCarInsuranceName1() {
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var result1 = CarInsuranceProcessing.getCarInsuranceName(Optional.ofNullable(person1));
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assertNotNull(result1);
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assertEquals(cambridgeInsurance.name(), result1);
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var result2 = CarInsuranceProcessing.getCarInsuranceName(Optional.ofNullable(person2));
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assertNotNull(result2);
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assertEquals("Unknown", result2);
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var result3 = CarInsuranceProcessing.getCarInsuranceName(Optional.ofNullable(person3));
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assertNotNull(result3);
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assertEquals("Unknown", result3);
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}
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@Test
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void testGetCarInsuranceName2() {
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var result1 = CarInsuranceProcessing.getCarInsuranceName(Optional.ofNullable(person1), 18);
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assertNotNull(result1);
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assertEquals(cambridgeInsurance.name(), result1);
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var result2 = CarInsuranceProcessing.getCarInsuranceName(Optional.ofNullable(person2), 18);
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assertNotNull(result2);
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assertEquals("Unknown", result2);
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var result3 = CarInsuranceProcessing.getCarInsuranceName(Optional.ofNullable(person3), 18);
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assertNotNull(result3);
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assertEquals("Unknown", result3);
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}
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@Test
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void testGetCarInsuranceNames() {
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var result = CarInsuranceProcessing.getCarInsuranceNames(List.of(person1, person2, person3));
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assertNotNull(result);
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assertEquals(1, result.size());
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assertEquals(cambridgeInsurance.name(), result.iterator().next());
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}
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@Test
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void testNullSafeFindCheapestInsurance() {
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var result1 = CarInsuranceProcessing.nullSafeFindCheapestInsurance(
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Optional.ofNullable(person1), Optional.ofNullable(car1));
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assertNotNull(result1);
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assertNotEquals(Optional.empty(), result1);
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var result2 = CarInsuranceProcessing.nullSafeFindCheapestInsurance(
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Optional.ofNullable(person2), Optional.empty());
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assertNotNull(result2);
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assertEquals(Optional.empty(), result2);
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var result3 = CarInsuranceProcessing.nullSafeFindCheapestInsurance(
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Optional.ofNullable(person3), Optional.ofNullable(car1));
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assertNotNull(result3);
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assertNotEquals(Optional.empty(), result3);
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}
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}

‎src/main/test/com/example/demo/chapter11/PropertyProcessingTest.java

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package com.example.demo.chapter11;
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import org.junit.jupiter.api.BeforeEach;
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import org.junit.jupiter.api.Test;
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import java.util.Optional;
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import java.util.Properties;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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class PropertyProcessingTest {
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private Properties props;
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@BeforeEach
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void setUp() {
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props = new Properties();
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props.setProperty("a", "5");
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props.setProperty("b", "true");
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props.setProperty("c", "-3");
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}
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@Test
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void testReadDurationImperative() {
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assertEquals(5, PropertyProcessing.readDurationImperative(props, "a"));
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assertEquals(0, PropertyProcessing.readDurationImperative(props, "b"));
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assertEquals(0, PropertyProcessing.readDurationImperative(props, "c"));
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assertEquals(0, PropertyProcessing.readDurationImperative(props, "d"));
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}
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@Test
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void testReadDurationWithOptional() {
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assertEquals(5, PropertyProcessing.readDurationWithOptional(props, "a"));
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assertEquals(0, PropertyProcessing.readDurationWithOptional(props, "b"));
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assertEquals(0, PropertyProcessing.readDurationWithOptional(props, "c"));
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assertEquals(0, PropertyProcessing.readDurationWithOptional(props, "d"));
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}
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@Test
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void testStringToOptionalInt() {
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var result1 = PropertyProcessing.stringToOptionalInt(props.getProperty("a"));
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assertEquals(5, result1.orElse(0));
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var result2 = PropertyProcessing.stringToOptionalInt(props.getProperty("b"));
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assertEquals(Optional.empty(), result2);
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var result3 = PropertyProcessing.stringToOptionalInt(props.getProperty("c"));
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assertEquals(-3, result3.orElse(0));
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}
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}

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