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[JAVA-26439] Moved code related to "Guide to Stream.reduce()" to ebook module (#15170)

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panos-kakos
2023-11-10 14:15:28 +00:00
committed by GitHub
parent 9cea810493
commit 7c1065b494
7 changed files with 15 additions and 218 deletions
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core-java-modules/core-java-8/src/main/java/com/baeldung/streamreduce/application/Application.java
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package com.baeldung.streamreduce.application;
import com.baeldung.streamreduce.entities.User;
import com.baeldung.streamreduce.utilities.NumberUtils;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class Application {
public static void main(String[] args) {
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
int result1 = numbers.stream().reduce(0, (a, b) -> a + b);
System.out.println(result1);
int result2 = numbers.stream().reduce(0, Integer::sum);
System.out.println(result2);
List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
String result3 = letters.stream().reduce("", (a, b) -> a + b);
System.out.println(result3);
String result4 = letters.stream().reduce("", String::concat);
System.out.println(result4);
String result5 = letters.stream().reduce("", (a, b) -> a.toUpperCase() + b.toUpperCase());
System.out.println(result5);
List<User> users = Arrays.asList(new User("John", 30), new User("Julie", 35));
int result6 = users.stream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
System.out.println(result6);
String result7 = letters.parallelStream().reduce("", String::concat);
System.out.println(result7);
int result8 = users.parallelStream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
System.out.println(result8);
List<User> userList = new ArrayList<>();
for (int i = 0; i <= 1000000; i++) {
userList.add(new User("John" + i, i));
}
long t1 = System.currentTimeMillis();
int result9 = userList.stream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
long t2 = System.currentTimeMillis();
System.out.println(result9);
System.out.println("Sequential stream time: " + (t2 - t1) + "ms");
long t3 = System.currentTimeMillis();
int result10 = userList.parallelStream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
long t4 = System.currentTimeMillis();
System.out.println(result10);
System.out.println("Parallel stream time: " + (t4 - t3) + "ms");
int result11 = NumberUtils.divideListElements(numbers, 1);
System.out.println(result11);
int result12 = NumberUtils.divideListElementsWithExtractedTryCatchBlock(numbers, 0);
System.out.println(result12);
}
}
core-java-modules/core-java-8/src/main/java/com/baeldung/streamreduce/entities/Rating.java
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package com.baeldung.streamreduce.entities;
import java.util.ArrayList;
import java.util.List;
public class Rating {
double points;
List<Review> reviews = new ArrayList<>();
public Rating() {}
public void add(Review review) {
reviews.add(review);
computeRating();
}
private double computeRating() {
double totalPoints = reviews.stream().map(Review::getPoints).reduce(0, Integer::sum);
this.points = totalPoints / reviews.size();
return this.points;
}
public static Rating average(Rating r1, Rating r2) {
Rating combined = new Rating();
combined.reviews = new ArrayList<>(r1.reviews);
combined.reviews.addAll(r2.reviews);
combined.computeRating();
return combined;
}
public double getPoints() {
return points;
}
public List<Review> getReviews() {
return reviews;
}
}
core-java-modules/core-java-8/src/main/java/com/baeldung/streamreduce/entities/Review.java
-28
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package com.baeldung.streamreduce.entities;
public class Review {
int points;
String review;
public Review(int points, String review) {
this.points = points;
this.review = review;
}
public int getPoints() {
return points;
}
public void setPoints(int points) {
this.points = points;
}
public String getReview() {
return review;
}
public void setReview(String review) {
this.review = review;
}
}
core-java-modules/core-java-8/src/main/java/com/baeldung/streamreduce/entities/User.java
-30
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package com.baeldung.streamreduce.entities;
public class User {
private final String name;
private final int age;
private final Rating rating = new Rating();
public User(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public int getAge() {
return age;
}
public Rating getRating() {
return rating;
}
@Override
public String toString() {
return "User{" + "name=" + name + ", age=" + age + '}';
}
}
core-java-modules/core-java-8/src/main/java/com/baeldung/streamreduce/utilities/NumberUtils.java
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package com.baeldung.streamreduce.utilities;
import java.util.List;
import java.util.function.BiFunction;
import java.util.logging.Level;
import java.util.logging.Logger;
public abstract class NumberUtils {
private static final Logger LOGGER = Logger.getLogger(NumberUtils.class.getName());
public static int divideListElements(List<Integer> values, Integer divider) {
return values.stream()
.reduce(0, (a, b) -> {
try {
return a / divider + b / divider;
} catch (ArithmeticException e) {
LOGGER.log(Level.INFO, "Arithmetic Exception: Division by Zero");
}
return 0;
});
}
public static int divideListElementsWithExtractedTryCatchBlock(List<Integer> values, int divider) {
return values.stream().reduce(0, (a, b) -> divide(a, divider) + divide(b, divider));
}
public static int divideListElementsWithApplyFunctionMethod(List<Integer> values, int divider) {
BiFunction<Integer, Integer, Integer> division = (a, b) -> a / b;
return values.stream().reduce(0, (a, b) -> applyFunction(division, a, divider) + applyFunction(division, b, divider));
}
private static int divide(int value, int factor) {
int result = 0;
try {
result = value / factor;
} catch (ArithmeticException e) {
LOGGER.log(Level.INFO, "Arithmetic Exception: Division by Zero");
}
return result;
}
private static int applyFunction(BiFunction<Integer, Integer, Integer> function, int a, int b) {
try {
return function.apply(a, b);
}
catch(Exception e) {
LOGGER.log(Level.INFO, "Exception occurred!");
}
return 0;
}
}
core-java-modules/core-java-8/src/test/java/com/baeldung/streamreduce/tests/StreamReduceManualTest.java
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package com.baeldung.streamreduce.tests;
import com.baeldung.streamreduce.entities.Rating;
import com.baeldung.streamreduce.entities.Review;
import com.baeldung.streamreduce.entities.User;
import com.baeldung.streamreduce.utilities.NumberUtils;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import static org.assertj.core.api.Assertions.assertThat;
import org.junit.Test;
public class StreamReduceManualTest {
@Test
public void givenIntegerList_whenReduceWithSumAccumulatorLambda_thenCorrect() {
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
int result = numbers.stream().reduce(0, (a, b) -> a + b);
assertThat(result).isEqualTo(21);
}
@Test
public void givenIntegerList_whenReduceWithSumAccumulatorMethodReference_thenCorrect() {
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
int result = numbers.stream().reduce(0, Integer::sum);
assertThat(result).isEqualTo(21);
}
@Test
public void givenStringList_whenReduceWithConcatenatorAccumulatorLambda_thenCorrect() {
List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
String result = letters.stream().reduce("", (a, b) -> a + b);
assertThat(result).isEqualTo("abcde");
}
@Test
public void givenStringList_whenReduceWithConcatenatorAccumulatorMethodReference_thenCorrect() {
List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
String result = letters.stream().reduce("", String::concat);
assertThat(result).isEqualTo("abcde");
}
@Test
public void givenStringList_whenReduceWithUppercaseConcatenatorAccumulator_thenCorrect() {
List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
String result = letters.stream().reduce("", (a, b) -> a.toUpperCase() + b.toUpperCase());
assertThat(result).isEqualTo("ABCDE");
}
@Test
public void givenUserList_whenReduceWithAgeAccumulatorAndSumCombiner_thenCorrect() {
List<User> users = Arrays.asList(new User("John", 30), new User("Julie", 35));
int result = users.stream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
assertThat(result).isEqualTo(65);
}
@Test
public void givenUserList_whenReduceWithGreaterAgeAccumulator_thenFindsOldest() {
List<User> users = Arrays.asList(new User("John", 30), new User("Alex", 40), new User("Julie", 35));
User oldest = users.stream().reduce(users.get(0), (user1, user2) -> user1.getAge() >= user2.getAge() ? user1 : user2);
assertThat(oldest).isEqualTo(users.get(1));
}
@Test
public void givenUserListWithRatings_whenReduceWithGreaterAgeAccumulator_thenFindsOldest() {
User john = new User("John", 30);
john.getRating().add(new Review(5, ""));
john.getRating().add(new Review(3, "not bad"));
User julie = new User("Julie", 35);
john.getRating().add(new Review(4, "great!"));
john.getRating().add(new Review(2, "terrible experience"));
john.getRating().add(new Review(4, ""));
List<User> users = Arrays.asList(john, julie);
Rating averageRating = users.stream().reduce(new Rating(), (rating, user) -> Rating.average(rating, user.getRating()), Rating::average);
assertThat(averageRating.getPoints()).isEqualTo(3.6);
}
@Test
public void givenStringList_whenReduceWithParallelStream_thenCorrect() {
List<String> letters = Arrays.asList("a", "b", "c", "d", "e");
String result = letters.parallelStream().reduce("", String::concat);
assertThat(result).isEqualTo("abcde");
}
@Test
public void givenNumberUtilsClass_whenCalledDivideListElements_thenCorrect() {
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
assertThat(NumberUtils.divideListElements(numbers, 1)).isEqualTo(21);
}
@Test
public void givenNumberUtilsClass_whenCalledDivideListElementsWithExtractedTryCatchBlock_thenCorrect() {
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
assertThat(NumberUtils.divideListElementsWithExtractedTryCatchBlock(numbers, 1)).isEqualTo(21);
}
@Test
public void givenNumberUtilsClass_whenCalledDivideListElementsWithExtractedTryCatchBlockAndListContainsZero_thenCorrect() {
List<Integer> numbers = Arrays.asList(0, 1, 2, 3, 4, 5, 6);
assertThat(NumberUtils.divideListElementsWithExtractedTryCatchBlock(numbers, 1)).isEqualTo(21);
}
@Test
public void givenNumberUtilsClass_whenCalledDivideListElementsWithExtractedTryCatchBlockAndDividerIsZero_thenCorrect() {
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
assertThat(NumberUtils.divideListElementsWithExtractedTryCatchBlock(numbers, 0)).isEqualTo(0);
}
@Test
public void givenStream_whneCalleddivideListElementsWithApplyFunctionMethod_thenCorrect() {
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6);
assertThat(NumberUtils.divideListElementsWithApplyFunctionMethod(numbers, 1)).isEqualTo(21);
}
@Test
public void givenTwoStreams_whenCalledReduceOnParallelizedStream_thenFasterExecutionTime() {
List<User> userList = new ArrayList<>();
for (int i = 0; i <= 1000000; i++) {
userList.add(new User("John" + i, i));
}
long currentTime1 = System.currentTimeMillis();
userList.stream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
long sequentialExecutionTime = System.currentTimeMillis() -currentTime1;
long currentTime2 = System.currentTimeMillis();
userList.parallelStream().reduce(0, (partialAgeResult, user) -> partialAgeResult + user.getAge(), Integer::sum);
long parallelizedExecutionTime = System.currentTimeMillis() - currentTime2;
assertThat(parallelizedExecutionTime).isLessThan(sequentialExecutionTime);
}
}