Streams

Question 1

What types of streams are there?

Answer 1

Finite and infinite

Question 2

How do we start finite streams?

Answer 2

Collection.stream()
Stream.of()
Stream.empty()

Question 3

How do we start infinite streams?

Answer 3

Stream.generate()
Stream.iterate(start, iterator)
Stream.iterate(start, end, iterator) -> can be finite

Question 4

Stream.filter(Predicate<? super T> predicate)

Answer 4

Filters elements of the stream based on a given predicate, keeping only those that satisfy the condition.

Question 5

How can we filter elements of the stream based on a given predicate?

Answer 5

Stream.filter(Predicate<? super T> predicate)

Question 6

Stream.distinct()

Answer 6

Returns a stream with distinct elements (removes duplicates).

Question 7

How can we remove duplicate elements from a stream?

Answer 7

Stream.distinct()

Question 8

Stream.limit(long maxSize)

Answer 8

Truncates the stream to be no longer than the given maximum size.

Question 9

How can we limit the number of elements in a stream?

Answer 9

Stream.limit(long maxSize)

Question 10

Stream.skip()

Answer 10

Returns a stream that skips the first n elements.

Question 11

How can we skip the first n elements of a stream?

Answer 11

Stream.skip(long n)

Question 12

Stream.map()

Answer 12

Transforms each element of the stream using the provided function.

Question 13

How can we transform each element of a stream using a function?

Answer 13

Stream.map(Function<? super T, ? extends R> mapper)

Question 14

Stream.flatMap()

Answer 14

Transforms each element into a stream of new elements and then flattens these streams into a single stream.

Question 15

How can we transform each element into a stream and flatten the result?

Answer 15

Stream.flatMap(Function<? super T, ? extends Stream<? extends R» mapper)

Question 16

Stream.sorted()

Answer 16

Returns a stream with elements sorted according to natural order or a provided comparator. Can hang app if used with infinite stream.

Question 17

How can we sort the elements of a stream?

Answer 17

Stream.sorted() or Stream.sorted(Comparator<? super T> comparator)

Question 18

Stream.peek()

Answer 18

Performs an action on each element of the stream without modifying it, useful for debugging.

Question 19

How can we perform an action on each element of a stream without modifying it?

Answer 19

Stream.peek(Consumer<? super T> action)

Question 20

What are intermediate streams?

Answer 20

filter, distinct, peek, skip, limit, map, flatMap, sorted.
They are intermediate because they are between starting operations and terminal operations.

Question 21

Name some terminal streams?

Answer 21

findAny, findFirst, allMatch, anyMatch, count, min, max, reduce, collect.
They are terminal because they close stream after they finish.

Question 22

Stream.forEach()

Answer 22

Performs an action for each element of the stream.

Question 23

How can we perform an action for each element of a stream?

Answer 23

Stream.forEach(Consumer<? super T> action)

Question 24

Stream.findAny()

Answer 24

Returns an Optional describing some element of the stream, or an empty Optional if the stream is empty.

Question 25

Stream.findFirst()

Answer 25

Returns an Optional describing the first element of the stream, or an empty Optional if the stream is empty.

Question 25

How can we retrieve any element from a stream?

Answer 25

Stream.findAny()

Question 26

How can we retrieve the first element of a stream?

Answer 26

Stream.findFirst()

Question 27

Stream.allMatch(Predicate predicate)

Answer 27

Returns whether all elements of the stream match the provided predicate.

Question 28

How can we check if all elements of a stream satisfy a given condition?

Answer 28

Stream.allMatch(Predicate predicate)

Question 29

Stream.anyMatch(Predicate predicate)

Answer 29

Returns whether any elements of the stream match the provided predicate.

Question 30

How can we check if at least one element of a stream satisfies a given condition?

Answer 30

Stream.anyMatch(Predicate predicate)

Question 30

How can we count the number of elements in a stream?

Answer 30

Stream.count()

Question 31

Stream.count()

Answer 31

Returns the count of elements in the stream.

Question 32

Stream.min(Comparator comparator)

Answer 32

Returns an Optional describing the minimum element of the stream according to the provided Comparator.

Question 33

How can we find the minimum element in a stream?

Answer 33

Stream.min(Comparator comparator)

Question 34

Stream.max(Comparator comparator)

Answer 34

Returns an Optional describing the maximum element of the stream according to the provided Comparator.

Question 35

How can we find the maximum element in a stream?

Answer 35

Stream.max(Comparator comparator)

Question 36

Stream.reduce()

Answer 36

Performs a reduction on the elements of the stream, using an associative accumulation function, and returns an Optional describing the reduced value, if any.

Question 37

How can we reduce the elements of a stream to a single value?

Answer 37

Stream.reduce(BinaryOperator accumulator)

Question 38

Stream.collect()

Answer 38

Performs a mutable reduction operation on the elements of the stream using a Collector.

Question 39

How can we perform a mutable reduction of the elements in a stream?

Answer 39

Stream.collect(Collector collector)

Question 40

What is spliterator?

Answer 40

It is util that is used to try and ideally split stream and then return one half. It detects infinite streams so app cannot hang using it. We use spliterator like: Spliterator spliterator = list.spliterator(); Then spliterator.trySplit() or spliterator.tryAdvance(), which gets next element in stream.

Question 41

Optional.empty()

Answer 41

Returns an empty Optional instance.

Question 42

How can we create an empty Optional?

Answer 42

Optional.empty()

Question 43

Optional.get()

Answer 43

Returns the value if present, otherwise throws NoSuchElementException.

Question 44

How can we retrieve the value from an Optional if it's present?

Answer 44

Optional.get()

Question 45

Optional.isPresent()

Answer 45

Returns true if there is a value present, otherwise false.

Question 46

How can we check if a value is present in an Optional?

Answer 46

Optional.isPresent()

Question 47

Optional.of()

Answer 47

Returns an Optional with the specified present non-null value.

Question 47

Optional.orElse()

Answer 47

Returns the value if present, otherwise returns the provided default value.

Question 47

How can we create an Optional with a non-null value?

Answer 47

Optional.of(T value)

Question 48

How can we get the value from an Optional or a default if it's not present?

Answer 48

Optional.orElse(T other)

Question 49

Optional.orElseGet()

Answer 49

Returns the value if present, otherwise invokes the provided supplier and returns its result.

Question 50

How can we get the value from an Optional or compute a default if it's not present?

Answer 50

Optional.orElseGet(Supplier supplier)

Question 51

Optional.orElseThrow()

Answer 51

Returns the contained value, if present, otherwise throws an exception produced by the provided supplier.

Question 52

Collectors.summarizingDouble/Long/Int()

Answer 52

Produces a summary of statistics for numeric stream elements.

Question 53

How can we generate summary statistics for numeric stream elements?

Answer 53

Collectors.summarizingDouble/Long/Int(ToDoubleFunction/ToLongFunction/ToIntFunction)

Question 54

Collectors.toCollection()

Answer 54

Collects stream elements into a specific Collection type.

Question 55

How can we collect stream elements into a specific Collection type?

Answer 55

Collectors.toCollection(Supplier collectionFactory)

Question 56

Collectors.toList()

Answer 56

Collects stream elements into a List.

Question 57

Collectors.toMap(Function keyMapper, Function valueMapper)

Answer 57

Collects stream elements into a Map.

Question 58

How can we collect stream elements into a List?

Answer 58

Collectors.toList()

Question 58

How can we collect stream elements into a Map?

Answer 58

Collectors.toMap(Function keyMapper, Function valueMapper)

Question 59

Collectors.toSet()

Answer 59

Collects stream elements into a Set.

Question 60

How can we collect stream elements into a Set?

Answer 60

Collectors.toSet()

Question 61

Collectors.joining(CharSequence delimiter)

Answer 61

Concatenates stream elements into a String with an optional delimiter.

Question 61

How can we partition stream elements into a Map based on a condition?

Answer 61

Collectors.partitioningBy(Predicate predicate)

Question 61

Collectors.partitioningBy(Predicate predicate)

Answer 61

Partitions stream elements into a Map based on a Predicate.

Question 62

How can we concatenate stream elements into a String with a delimiter?

Answer 62

Collectors.joining(CharSequence delimiter)

Question 63

Collectors.groupingBy()

Answer 63

Groups stream elements into a Map based on a classification function.

Question 64

How can we group stream elements into a Map based on a classification function?

Answer 64

Collectors.groupingBy(Function classifier)

Question 65

Collectors.teeing(Collector downstream1, Collector downstream2, BiFunction merger)

Answer 65

Combines two collectors into a single one.

Question 66

How can we combine two collectors into a single collector?

Answer 66

Collectors.teeing(Collector downstream1, Collector downstream2, BiFunction merger)

Question 67

IntStream, LongStream, DoubleStream?

Answer 67

Stream creating classes that create stream for primitives using range() and rangeClosed()

Question 68

How can we get max, min, average or sum using Streams?

Answer 68

Using IntStream, LongStream, DoubleStream

Question 69

How can we summarize statistics using Streams?

Answer 69

Calling summaryStatistics() on IntStream, LongStream, DoubleStream. Then we can getAverage(), getCount(), getMin(), getMax()

Question 70

How can we map to other objects from IntStream, LongStream, DoubleStream?

Answer 70

Calling map(), mapTo(), mapToObj()