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Commit 84eb88a

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CrazyLambdas upgrade
* add method comparing * add method thenComparing * cover those methods with tests
1 parent e3d1b8e commit 84eb88a

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‎5-0-functional-programming/5-1-1-crazy-lambdas/src/main/java/com/bobocode/fp/CrazyLambdas.java‎

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import com.bobocode.util.ExerciseNotCompletedException;
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import java.math.BigDecimal;
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import java.util.Comparator;
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import java.util.Map;
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import java.util.function.*;
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@@ -190,6 +191,44 @@ public static BiFunction<Map<String, IntUnaryOperator>, String, IntUnaryOperator
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throw new ExerciseNotCompletedException();
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}
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/**
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* Returns a comparator of type T that is comparing values extracted using the provided mapper function.
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* <p>
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* E.g. imagine you need to compare accounts by their balance values.
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* <pre>{@code
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* Comparator<Account> balanceComparator = comparing(Account::getBalance);
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* }</pre>
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* <p>
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* PLEASE NOTE, that @{@link Comparator} is a functional interface, and you should manually write a lambda expression
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* to implement it.
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*
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* @param mapper a mapper function that allows to map an object to a comparable value
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* @return a comparator instance
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*/
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public static <T, U extends Comparable<? super U>> Comparator<T> comparing(Function<? super T, ? extends U> mapper) {
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throw new ExerciseNotCompletedException();
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}
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/**
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* Returns a comparator of type T that uses a provided comparator to compare objects, and only if they are equal
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* it's comparing values extracted using the provided mapper function.
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* <p>
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* E.g. suppose you want to compare accounts by balance, but in case two people have the same balance you want to
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* compare their first names:
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* <pre>{@code
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* Comparator<Account> accountComparator = thenComparing(balanceComparator, Account::getFirstName);
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* }</pre>
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* <p>
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*
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* @param comparator an initial comparator
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* @param mapper a mapper function that is used to extract values when initial comparator returns zero
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* @return a comparator instance
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*/
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public static <T, U extends Comparable<? super U>> Comparator<T> thenComparing(
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Comparator<? super T> comparator, Function<? super T, ? extends U> mapper) {
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throw new ExerciseNotCompletedException();
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}
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/**
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* Returns {@link Supplier} of {@link Supplier} of {@link Supplier} of {@link String} "WELL DONE!".
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*

‎5-0-functional-programming/5-1-1-crazy-lambdas/src/test/java/com/bobocode/fp/CrazyLambdasTest.java‎

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import org.junit.jupiter.api.TestMethodOrder;
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import java.math.BigDecimal;
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import java.util.HashMap;
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import java.util.Map;
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import java.util.Queue;
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import java.util.*;
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import java.util.concurrent.ConcurrentLinkedQueue;
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import java.util.function.*;
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import static org.assertj.core.api.Assertions.assertThat;
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import static org.junit.jupiter.api.Assertions.*;
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/**
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@Test
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@Order(18)
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void comparing() {
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var strLengthComparator = CrazyLambdas.comparing(String::length);
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var stringList = new ArrayList<>(List.of("Me", "I", "All of us", "They", "She"));
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stringList.sort(strLengthComparator);
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assertThat(stringList).isEqualTo(List.of("I", "Me", "She", "They", "All of us"));
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}
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@Test
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@Order(19)
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void thenComparing() {
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var strLengthComparator = Comparator.comparing(String::length);
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var lengthThenNaturalComparator = CrazyLambdas.thenComparing(strLengthComparator, s -> s);
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var stringList = new ArrayList<>(List.of("Me", "I", "All of us", "They", "She", "He"));
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stringList.sort(lengthThenNaturalComparator);
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assertThat(stringList).isEqualTo(List.of("I", "He", "Me", "She", "They", "All of us"));
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}
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@Test
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@Order(20)
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void trickyWellDoneSupplier() {
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Supplier<Supplier<Supplier<String>>> wellDoneSupplier = CrazyLambdas.trickyWellDoneSupplier();
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