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Stanislav-ZabramnyiStanislav-Zabramnyi
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GP-155: add random-field-comparator exercise (#135)
* GP-155: add random-field-comparator exercise
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‎3-0-java-core/3-6-4-random-field-comparator/README.MD

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# <img src="https://raw.githubusercontent.com/bobocode-projects/resources/master/image/logo_transparent_background.png" height=50/>Random Field Comparator
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#### Improve your reflection-related skills implementing a random field comparator 💪
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### Objectives
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* implement a logic of choosing a random field to use it for comparison of objects of provided type ✅
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* implement a mechanism to check if field type is `Comparable` ✅
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* implement a method `compare` that compares two objects by randomly-provided field ✅
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* extend a method `compare` to manage null field values following condition when null value greater than a non-null value ✅
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* implement method `getComparingFieldName` that retrieves the name of randomly-chosen comparing field✅
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* implement method `toString` ✅
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---
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#### 🆕 First time here? – [See Introduction](https://github.com/bobocode-projects/java-fundamentals-exercises/tree/main/0-0-intro#introduction)
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#### ➡️ Have any feedback? – [Please fill the form ](https://forms.gle/u6kHcecFuzxV232LA)
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##
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<div align="center"><img src="https://raw.githubusercontent.com/bobocode-projects/resources/master/animation/GitHub%20Star_3.gif" height=50/></div>

‎3-0-java-core/3-6-4-random-field-comparator/pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<parent>
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<artifactId>3-0-java-core</artifactId>
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<groupId>com.bobocode</groupId>
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<version>1.0-SNAPSHOT</version>
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</parent>
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<modelVersion>4.0.0</modelVersion>
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<artifactId>3-6-4-random-field-comparator</artifactId>
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</project>

‎3-0-java-core/3-6-4-random-field-comparator/src/main/java/com/bobocode/se/RandomFieldComparator.java

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package com.bobocode.se;
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import com.bobocode.util.ExerciseNotCompletedException;
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import java.util.Comparator;
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/**
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* A generic comparator that is comparing a random field of the given class. The field is either primitive or
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* {@link Comparable}. It is chosen during comparator instance creation and is used for all comparisons.
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* <p>
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* If no field is available to compare, the constructor throws {@link IllegalArgumentException}
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*
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* @param <T> the type of the objects that may be compared by this comparator
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*<p><p>
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* <strong>TODO: to get the most out of your learning, <a href="https://www.bobocode.com/learn">visit our website</a></strong>
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* <p>
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*
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* @author Stanislav Zabramnyi
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*/
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public class RandomFieldComparator<T> implements Comparator<T> {
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public RandomFieldComparator(Class<T> targetType) {
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throw new ExerciseNotCompletedException(); // todo: implement this constructor;
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}
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/**
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* Compares two objects of the class T by the value of the field that was randomly chosen. It allows null values
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* for the fields, and it treats null value greater than a non-null value.
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*
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* @param o1
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* @param o2
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* @return positive int in case of first parameter {@param o1} is greater than second one {@param o2},
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* zero if objects are equals,
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* negative int in case of first parameter {@param o1} is less than second one {@param o2}.
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*/
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@Override
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public int compare(T o1, T o2) {
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throw new ExerciseNotCompletedException(); // todo: implement this method;
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}
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/**
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* Returns the name of the randomly-chosen comparing field.
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*/
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public String getComparingFieldName() {
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throw new ExerciseNotCompletedException(); // todo: implement this method;
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}
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/**
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* Returns a statement "Random field comparator of class '%s' is comparing '%s'" where the first param is the name
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* of the type T, and the second parameter is the comparing field name.
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*
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* @return a predefined statement
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*/
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@Override
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public String toString() {
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throw new ExerciseNotCompletedException(); // todo: implement this method;
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}
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}

‎3-0-java-core/3-6-4-random-field-comparator/src/test/java/com/bobocode/se/RandomFieldComparatorTest.java

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package com.bobocode.se;
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import static org.assertj.core.api.AssertionsForClassTypes.assertThat;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertThrows;
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import java.lang.reflect.Field;
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import java.util.Arrays;
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import lombok.AllArgsConstructor;
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import lombok.NoArgsConstructor;
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import lombok.SneakyThrows;
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import org.junit.jupiter.api.DisplayName;
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import org.junit.jupiter.api.MethodOrderer.OrderAnnotation;
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import org.junit.jupiter.api.Order;
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import org.junit.jupiter.api.Test;
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import org.junit.jupiter.api.TestMethodOrder;
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@TestMethodOrder(OrderAnnotation.class)
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class RandomFieldComparatorTest {
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private final RandomFieldComparator<Account> randomFieldComparator = new RandomFieldComparator<>(Account.class);
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@Test
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@Order(1)
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@DisplayName("Constructor throws an exception when parameter is null")
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void classDoesNotApplyNullInConstructor() {
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assertThrows(NullPointerException.class, () -> new RandomFieldComparator<>(null));
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}
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@Test
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@Order(2)
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@SneakyThrows
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@DisplayName("Constructor throws an exception when the target type has no Comparable fields")
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void constructorThrowsExceptionIfNoComparableFieldsInProvidedType() {
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assertThrows(IllegalArgumentException.class, () -> new RandomFieldComparator<>(ClassWithNotComparableField.class));
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}
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@Test
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@Order(3)
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@DisplayName("Method 'compare' throws an exception when any parameter is null")
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void compareWhenFirstParameterAreNull() {
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assertThrows(NullPointerException.class, () -> randomFieldComparator.compare(null, new Account()));
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assertThrows(NullPointerException.class, () -> randomFieldComparator.compare(new Account(), null));
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}
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@Test
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@Order(4)
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@DisplayName("Method 'compare' returns 0 when field values of both objects are null")
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void compareWhenBothFieldValuesIsNull() {
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setFieldToCompare("lastName", Account.class);
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int compareResult = randomFieldComparator.compare(new Account(), new Account());
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assertThat(compareResult).isZero();
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}
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@Test
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@Order(5)
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@DisplayName("Method compare returns positive int when the first field value is null")
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void compareWhenFieldValuesOfFirstObjectIsNull() {
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Account emptyAccount = new Account();
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Account account = new Account("Sibma", "LoinKing", "[email protected]", 14);
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setFieldToCompare("email", Account.class);//set field to compare explicitly as there are int field which has default value 0
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int compareResult = randomFieldComparator.compare(emptyAccount, account);
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assertThat(compareResult).isPositive();
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}
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@Test
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@Order(6)
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@DisplayName("Method compare returns negative int when the second field value is null")
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void compareWhenFieldValuesOfSecondObjectIsNull() {
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Account account = new Account("Mufasa", "LoinKing", "[email protected]", 47);
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Account emptyAccount = new Account();
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setFieldToCompare("firstName", Account.class);
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int compareResult = randomFieldComparator.compare(account, emptyAccount);
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assertThat(compareResult).isNegative();
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}
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@Test
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@Order(7)
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@SneakyThrows
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@DisplayName("Method 'compare' returns positive int when the first value is greater")
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void compareWhenFieldValueOfFirstObjectIsGreater() {
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var fieldToCompareName = "firstName";
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Account account1 = new Account();
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Account account2 = new Account();
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Field fieldToCompareAccount = account1.getClass().getDeclaredField(fieldToCompareName);
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fieldToCompareAccount.setAccessible(true);
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fieldToCompareAccount.set(account1, "Bob");
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fieldToCompareAccount.set(account2, "Alice");
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setFieldToCompare(fieldToCompareName, Account.class);
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int compareResult = randomFieldComparator.compare(account1, account2);
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assertThat(compareResult).isPositive();
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}
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@Test
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@Order(8)
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@SneakyThrows
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@DisplayName("Method 'compare' returns negative int when the first value is smaller")
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void compareWhenFieldValueOfSecondObjectIsGreater() {
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var fieldToCompareName = "firstName";
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Account account1 = new Account();
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Account account2 = new Account();
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Field fieldToCompareAccount = account1.getClass().getDeclaredField(fieldToCompareName);
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fieldToCompareAccount.setAccessible(true);
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fieldToCompareAccount.set(account1, "Alice");
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fieldToCompareAccount.set(account2, "Bob");
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setFieldToCompare(fieldToCompareName, Account.class);
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int compareResult = randomFieldComparator.compare(account1, account2);
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assertThat(compareResult).isNegative();
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}
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@Test
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@Order(9)
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@SneakyThrows
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@DisplayName("Method 'compare' returns zero when the field values are equal")
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void compareWhenFieldValuesOfObjectsAreEqual() {
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var fieldToCompareName = "firstName";
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Account account1 = new Account();
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Account account2 = new Account();
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Field fieldToCompareAccount = account1.getClass().getDeclaredField(fieldToCompareName);
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fieldToCompareAccount.setAccessible(true);
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fieldToCompareAccount.set(account1, "Carol");
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fieldToCompareAccount.set(account2, "Carol");
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setFieldToCompare(fieldToCompareName, Account.class);
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int compareResult = randomFieldComparator.compare(account1, account2);
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assertThat(compareResult).isZero();
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}
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@Test
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@Order(10)
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@SneakyThrows
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@DisplayName("Method 'compare' returns positive int when the first primitive value is greater")
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void comparePrimitivesWhenFieldValueOfFirstObjectIsGreater() {
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var fieldToCompareName = "age";
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Account account1 = new Account();
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Account account2 = new Account();
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Field fieldToCompareAccount = account1.getClass().getDeclaredField(fieldToCompareName);
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fieldToCompareAccount.setAccessible(true);
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fieldToCompareAccount.setInt(account1, 7);
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fieldToCompareAccount.setInt(account2, 3);
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setFieldToCompare(fieldToCompareName, Account.class);
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int compareResult = randomFieldComparator.compare(account1, account2);
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assertThat(compareResult).isPositive();
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}
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@Test
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@Order(11)
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@SneakyThrows
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@DisplayName("Method 'compare' returns zero when the primitive field values are equal")
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void comparePrimitivesWhenFieldValuesOfObjectsAreEqual() {
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var fieldToCompareName = "age";
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Account account1 = new Account();
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Account account2 = new Account();
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Field fieldToCompareAccount = account1.getClass().getDeclaredField(fieldToCompareName);
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fieldToCompareAccount.setAccessible(true);
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fieldToCompareAccount.setInt(account1, 15);
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fieldToCompareAccount.setInt(account2, 15);
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setFieldToCompare(fieldToCompareName, Account.class);
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int compareResult = randomFieldComparator.compare(account1, account2);
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assertThat(compareResult).isZero();
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}
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@Test
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@Order(12)
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@SneakyThrows
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@DisplayName("Method 'compare' returns negative int when the first primitive value is smaller")
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void comparePrimitivesWhenFieldValueOfSecondObjectIsGreater() {
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var fieldToCompareName = "age";
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Account account1 = new Account();
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Account account2 = new Account();
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Field fieldToCompareAccount = account1.getClass().getDeclaredField(fieldToCompareName);
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fieldToCompareAccount.setAccessible(true);
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fieldToCompareAccount.setInt(account1, 4);
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fieldToCompareAccount.setInt(account2, 8);
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setFieldToCompare(fieldToCompareName, Account.class);
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int compareResult = randomFieldComparator.compare(account1, account2);
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assertThat(compareResult).isNegative();
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}
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@Test
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@Order(13)
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@SneakyThrows
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@DisplayName("Method 'getComparingFieldName' returns the name of randomly-chosen field to be compared")
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void getComparingFieldName() {
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var fieldToCompareName = "lastName";
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setFieldToCompare(fieldToCompareName, Account.class);
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assertEquals(fieldToCompareName, randomFieldComparator.getComparingFieldName());
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}
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@Test
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@Order(14)
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@SneakyThrows
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@DisplayName("Method toString is properly overridden")
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void toStringOverriding() {
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var expectedString = "Random field comparator of class 'Account' is comparing 'email'";
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var fieldToCompareName = "email";
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setFieldToCompare(fieldToCompareName, Account.class);
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assertEquals(expectedString, randomFieldComparator.toString());
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}
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@SneakyThrows
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private <T> void setFieldToCompare(String fieldName, Class<T> classType) {
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Field fieldToCompare = Arrays.stream(randomFieldComparator.getClass().getDeclaredFields())
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.filter(f -> f.getType().equals(Field.class))
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.findAny()
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.orElseThrow();
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fieldToCompare.setAccessible(true);
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fieldToCompare.set(randomFieldComparator, classType.getDeclaredField(fieldName));
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}
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private static class EmptyClass {
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}
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@AllArgsConstructor
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private static class ClassWithNotComparableField {
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private Object field;
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}
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@NoArgsConstructor
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@AllArgsConstructor
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private static class Account {
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private String firstName;
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private String lastName;
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private String email;
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private int age;
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}
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}

‎3-0-java-core/pom.xml

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<module>3-6-1-file-reader</module>
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<module>3-6-2-file-stats</module>
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<module>3-6-3-crazy-regex</module>
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<module>3-6-4-random-field-comparator</module>
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</modules>
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