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June 10, 2021 08:53
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import org.assertj.core.api.Assertions; | |
import org.junit.jupiter.api.Test; | |
import java.util.*; | |
import java.util.function.Function; | |
import java.util.function.Predicate; | |
import java.util.stream.Collectors; | |
import java.util.stream.IntStream; | |
import java.util.stream.Stream; | |
import java.util.stream.StreamSupport; | |
public class MyTop25FavoriteJDKMethodsTest { | |
private final List<String> fruit = | |
List.of("apple", "apricot", "banana", "blueberry", "clementine"); | |
private final Set<String> onlyBanana = | |
Set.of("banana"); | |
@Test | |
public void with() { | |
List<String> fruit = | |
new ArrayList<>(List.of("apple", "apricot", "banana", "blueberry", "clementine")); | |
List<String> expected = | |
Arrays.asList("apple", "apricot", "banana", "blueberry", "clementine"); | |
Assertions.assertThat(expected).containsExactly("apple", "apricot", "banana", "blueberry", "clementine"); | |
} | |
@Test | |
public void collect() { | |
List<String> uppercase = this.fruit.stream().map(String::toUpperCase).toList(); | |
List<String> expected = | |
Arrays.asList("APPLE", "APRICOT", "BANANA", "BLUEBERRY", "CLEMENTINE"); | |
Assertions.assertThat(expected).containsExactly("APPLE", "APRICOT", "BANANA", "BLUEBERRY", "CLEMENTINE"); | |
} | |
@Test | |
public void of() { | |
Set<String> onlyBanana = new HashSet<>(Set.of("banana")); | |
Assertions.assertThat(onlyBanana).containsExactly("banana"); | |
} | |
@Test | |
public void select() { | |
List<String> justBanana = this.fruit.stream().filter(onlyBanana::contains).toList(); | |
Assertions.assertThat(justBanana).containsExactly("banana"); | |
} | |
@Test | |
public void reject() { | |
// ImmutableList<String> notBanana = this.fruit.reject(this.onlyBanana::contains); | |
List<String> notBanana = this.fruit.stream().filter(Predicate.not(onlyBanana::contains)).toList(); | |
Assertions.assertThat(notBanana).containsExactly("apple", "apricot", "blueberry", "clementine"); | |
} | |
@Test | |
public void count() { | |
long countBanana = this.fruit.stream().filter(onlyBanana::contains).count(); | |
long countAll = this.fruit.stream().filter(fruit::contains).count(); | |
Assertions.assertThat(countBanana).isEqualTo(1L); | |
Assertions.assertThat(countAll).isEqualTo(5L); | |
} | |
@Test | |
public void anySatisfy() { | |
boolean anyBanana = this.fruit.stream().anyMatch(this.onlyBanana::contains); | |
boolean anyEmpty = this.fruit.stream().anyMatch(String::isEmpty); | |
Assertions.assertThat(anyBanana).isTrue(); | |
Assertions.assertThat(anyEmpty).isFalse(); | |
} | |
@Test | |
public void allSatisfy() { | |
boolean allBanana = this.fruit.stream().allMatch(this.onlyBanana::contains); | |
boolean allLowercase = | |
this.fruit.stream().allMatch(string -> | |
IntStream.range(0, string.length()).mapToObj(string::charAt).allMatch(Character::isLowerCase)); | |
Assertions.assertThat(allBanana).isFalse(); | |
Assertions.assertThat(allLowercase).isTrue(); | |
} | |
@Test | |
public void noneSatisfy() { | |
boolean noneBanana = this.fruit.stream().noneMatch(onlyBanana::contains); | |
boolean noneEmpty = this.fruit.stream().noneMatch(String::isEmpty); | |
Assertions.assertThat(noneBanana).isFalse(); | |
Assertions.assertThat(noneEmpty).isTrue(); | |
} | |
@Test | |
public void groupBy() { | |
Map<Character, List<String>> multimap = | |
this.fruit.stream().collect( | |
Collectors.collectingAndThen( | |
Collectors.groupingBy(fruit -> fruit.charAt(0)), | |
Collections::unmodifiableMap)); | |
Assertions.assertThat(multimap.get('a')).containsExactly("apple", "apricot"); | |
Assertions.assertThat(multimap.get('b')).containsExactly("banana", "blueberry"); | |
Assertions.assertThat(multimap.get('c')).containsExactly("clementine"); | |
} | |
@Test | |
public void countBy() { | |
Map<Character, Long> firstLetterCounts = | |
this.fruit.stream().collect( | |
Collectors.collectingAndThen( | |
Collectors.groupingBy(fruit -> fruit.charAt(0), Collectors.counting()), | |
Collections::unmodifiableMap)); | |
Assertions.assertThat(firstLetterCounts.get('a')).isEqualTo(2L); | |
Assertions.assertThat(firstLetterCounts.get('b')).isEqualTo(2L); | |
Assertions.assertThat(firstLetterCounts.get('c')).isEqualTo(1L); | |
} | |
@Test | |
public void makeString() { | |
String fruitString = this.fruit.stream().collect(Collectors.joining(",", "(", ")")); | |
Assertions.assertThat(fruitString).isEqualTo("(apple,apricot,banana,blueberry,clementine)"); | |
} | |
@Test | |
public void toImmutable() { | |
List<String> mutableFruit = | |
new ArrayList<>(List.of("apple", "apricot", "banana", "blueberry", "clementine")); | |
List<String> immutableFruit = Collections.unmodifiableList(mutableFruit); | |
Assertions.assertThat(immutableFruit).containsExactly("apple", "apricot", "banana", "blueberry", "clementine"); | |
} | |
@Test | |
public void asLazy() { | |
Iterable<String> fruitIterable = this.fruit::iterator; | |
Stream<String> stream = StreamSupport.stream(fruit.spliterator(), false); | |
Assertions.assertThat(stream.count()).isEqualTo(5L); | |
} | |
@Test | |
public void containsBy() { | |
boolean hasApple = this.fruit.stream().map(String::toUpperCase).anyMatch("APPLE"::equals); | |
boolean hasTomato = this.fruit.stream().map(String::toUpperCase).anyMatch("TOMATO"::equals); | |
Assertions.assertThat(hasApple).isTrue(); | |
Assertions.assertThat(hasTomato).isFalse(); | |
} | |
@Test | |
public void detectWith() { | |
String banana = this.fruit.stream().filter(s -> s.startsWith("b")).findAny().orElse(null); | |
String none = this.fruit.stream().filter(s -> s.startsWith("d")).findAny().orElse(null); | |
Assertions.assertThat(banana).isEqualTo("banana"); | |
Assertions.assertThat(none).isNull(); | |
} | |
@Test | |
public void detectWithIfNone() { | |
String banana = this.fruit.stream().filter(s -> s.startsWith("b")).findAny().orElseGet(() -> "apple"); | |
String stillBanana = this.fruit.stream().filter(s -> s.startsWith("b")).findAny().orElseGet(() -> "banana"); | |
Assertions.assertThat(banana).isEqualTo("banana"); | |
Assertions.assertThat(stillBanana).isEqualTo("banana"); | |
} | |
@Test | |
public void injectInto() { | |
String mixedFruitString = this.fruit.stream().collect(Collectors.joining()); | |
Assertions.assertThat(mixedFruitString).isEqualTo("appleapricotbananablueberryclementine"); | |
} | |
@Test | |
public void partition() { | |
Map<Boolean, List<String>> partitionFruit = | |
this.fruit.stream().collect( | |
Collectors.collectingAndThen( | |
Collectors.partitioningBy(fruit -> fruit.length() > 6), | |
map -> Map.of(true, Collections.unmodifiableList(map.get(true)), | |
false, Collections.unmodifiableList(map.get(false))) | |
)); | |
List<String> selected = partitionFruit.get(true); | |
List<String> rejected = partitionFruit.get(false); | |
Assertions.assertThat(selected).containsExactly("apricot", "blueberry", "clementine"); | |
Assertions.assertThat(rejected).containsExactly("apple", "banana"); | |
} | |
@Test | |
public void chunk() { | |
record ChunkIndexes(int fromIndex, int toIndex) { | |
<T> List<T> applyTo(List<T> list) { | |
return list.subList(fromIndex, toIndex); | |
} | |
} | |
record Indexes(int listSize, int chunkSize) { | |
List<ChunkIndexes> chunkIndexes() { | |
return IntStream.range(0, listSize) | |
.filter(index -> index % chunkSize == 0) | |
.mapToObj(index -> new ChunkIndexes(index, Integer.min(listSize, index + chunkSize))) | |
.collect(Collectors.toList()); | |
} | |
} | |
List<List<String>> chunkFruit = | |
new Indexes(this.fruit.size(), 2) | |
.chunkIndexes().stream() | |
.map(chunkIndexes -> chunkIndexes.applyTo(this.fruit)) | |
.collect(Collectors.toList()); | |
Assertions.assertThat(chunkFruit.size()).isEqualTo(3); | |
Assertions.assertThat(chunkFruit.get(0)).containsExactly("apple", "apricot"); | |
Assertions.assertThat(chunkFruit.get(2)).containsExactly("clementine"); | |
} | |
@Test | |
public void sumByInt() { | |
Map<Character, Integer> sumLengthsByFirstCharacter = | |
this.fruit.stream() | |
.collect( | |
Collectors.collectingAndThen( | |
Collectors.groupingBy( | |
fruit -> fruit.charAt(0), | |
Collectors.summingInt(String::length)), | |
Collections::unmodifiableMap | |
)); | |
Assertions.assertThat(sumLengthsByFirstCharacter.get('a')).isEqualTo(12); | |
Assertions.assertThat(sumLengthsByFirstCharacter.get('b')).isEqualTo(15); | |
Assertions.assertThat(sumLengthsByFirstCharacter.get('c')).isEqualTo(10); | |
} | |
@Test | |
public void collectInt() { | |
List<Integer> lengths = this.fruit.stream().map(String::length).collect(Collectors.toList()); | |
Assertions.assertThat(lengths).containsExactly(5, 7, 6, 9, 10); | |
} | |
@Test | |
public void flatCollectChar() { | |
Map<Character, Long> charCounts = | |
this.fruit.stream() | |
.flatMap(word -> IntStream.range(0, word.length()).mapToObj(word::charAt)) | |
.collect(Collectors.groupingBy( | |
Function.identity(), Collectors.counting() | |
)); | |
Assertions.assertThat(charCounts.get('a')).isEqualTo(5); | |
Assertions.assertThat(charCounts.get('b')).isEqualTo(3); | |
Assertions.assertThat(charCounts.get('c')).isEqualTo(2); | |
} | |
@Test | |
public void asParallel() { | |
List<String> onlyBananaList = | |
this.fruit.parallelStream() | |
.filter(this.onlyBanana::contains) | |
.collect(Collectors.toList()); | |
Set<String> onlyBananaSet = | |
this.fruit.parallelStream() | |
.filter(this.onlyBanana::contains) | |
.collect(Collectors.toSet()); | |
Assertions.assertThat(onlyBananaList).containsExactly("banana"); | |
Assertions.assertThat(onlyBananaSet).containsExactly("banana"); | |
} | |
@Test | |
public void distinct() { | |
List<String> duplicateFruit = List.of("apple", "apple", "banana", "banana"); | |
List<String> distinctFruit = duplicateFruit.stream().distinct().collect(Collectors.toList()); | |
Assertions.assertThat(distinctFruit).containsExactly("apple", "banana"); | |
} | |
} |
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