Streams
Framework for processing sequences of data in declarative and functional style. Basically, you can specify an operation and perform it for all items in the collection.
Introduced in Version#8.
Methods
Intermediate Operations
Intermediate operations return a stream.
filter(lang.java.lib.interfaces.func.function.predicate)
Filters elements based on a condition.
List<Integer> evens = numbers.stream()
.filter(n -> n % 2 == 0)
.collect(Collectors.toList());
map(lang.java.lib.interfaces.func.function)
Transform each element of the stream.
List<String> upperNames = names.stream()
.map(String::toUpperCase)
.collect(Collectors.toList());
flatMap(lang.java.lib.interfaces.func.function)
Flattens stream of streams into a single stream.
List<String> allWords = sentences.stream()
.flatMap(sentence -> Arrays.stream(sentence.split(" ")))
.collect(Collectors.toList());
Stream<List<Integer>> nestedStream = Stream.of(List.of(1, 2), List.of(3, 4));
Stream<Integer> flattenedStream = nestedStream.flatMap(List::stream);
distinct()
Removes duplicates.
List<Integer> uniqueNumbers = numbers.stream()
.distinct()
.collect(Collectors.toList());
sorted() and sorted(lang.java.lib.interfaces.func.comparator)
Sorts by natural order or by Comparator, if passed.
List<String> sortedNames = names.stream()
.sorted()
.collect(Collectors.toList());
List<Person> sortedByAge = people.stream()
.sorted(Comparator.comparing(Person::getAge))
.collect(Collectors.toList());
peek(lang.java.lib.interfaces.func.consumer)
Performs an action on each element without altering the stream.
numbers.stream()
.peek(n -> System.out.println("Processing number: " + n))
.collect(Collectors.toList());
limit(long n)
Limits the stream to first n elements.
List<Integer> firstThree = numbers.stream()
.limit(3)
.collect(Collectors.toList());
skip(long n)
Skips the first n elements.
List<Integer> withoutFirstTwo = numbers.stream()
.skip(2)
.collect(Collectors.toList());
Terminal Operations
These operations consume the stream and return a result.
forEach(lang.java.lib.interfaces.func.consumer)
Performs an operation for each element.
names.stream().forEach(System.out::println);
collect(Collector)
Collects the stream into a collection.
Instance of Collector can be fetched from lang.java.lib.classes.collectors API.
List<String> collectedNames = names.stream().collect(Collectors.toList());
<U> U reduce(U identity, lang.java.lib.interfaces.func.function.BinaryOperator accumulator)
Reduces stream to a single value.
identityvalue is used as the initial valueaccumulatorfunction is used to combine all the elements.
int sum = numbers.stream()
.reduce(0, Integer::sum);
toArray()
Converts stream into array.
String[] nameArray = names.stream().toArray(String[]::new);
min(lang.java.lib.interfaces.func.comparator) and max(lang.java.lib.interfaces.func.comparator)
Optional<Integer> min = numbers.stream()
.min(Comparator.naturalOrder());
count()
long count = numbers.stream().count();
anyMatch(lang.java.lib.interfaces.func.function.predicate), allMatch(lang.java.lib.interfaces.func.function.predicate) and noneMatch(lang.java.lib.interfaces.func.function.predicate)
boolean hasEven = numbers.stream()
.anyMatch(n -> n % 2 == 0);
findFirst()
Optional<Integer> first = numbers.stream()
.findFirst();
findAny()
Optional<Integer> any = numbers.stream()
.findAny();
Collectors
Utility class which provides implementation of Collector interface, which is then used to get a collection or other data form from a stream.
Methods
-
toList()
-
toSet()
-
toMap()
