Summary of Intermediate Stream Operations – Streams

Summary of Intermediate Stream Operations

Table 16.3 summarizes selected aspects of the intermediate operations.

Table 16.3 Selected Aspects of Intermediate Stream Operations

Intermediate operation	Stateful/Stateless	Can change stream size	Can change stream type	Encounter order
distinct (p. 915)	Stateful	Yes	No	Unchanged
dropWhile (p. 913)	Stateful	Yes	No	Unchanged
filter (p. 910)	Stateless	Yes	No	Unchanged
flatMap (p. 921)	Stateless	Yes	Yes	Not guaranteed
limit (p. 917)	Stateful, short-circuited	Yes	No	Unchanged
map (p. 921)	Stateless	No	Yes	Not guaranteed
mapMulti (p. 927)	Stateless	Yes	Yes	Not guaranteed
parallel (p. 933)	Stateless	No	No	Unchanged
peek (p. 920)	Stateless	No	No	Unchanged
sequential (p. 933)	Stateless	No	No	Unchanged
skip (p. 915)	Stateful	Yes	No	Unchanged
sorted (p. 929)	Stateful	No	No	Ordered
takeWhile (p. 913)	Stateful, short-circuited	Yes	No	Unchanged
unordered (p. 932)	Stateless	No	No	Not guaranteed

The intermediate operations of the Stream<T> interface (including those inherited from its superinterface BaseStream<T,Stream<T>>) are summarized in Table 16.4. The type parameter declarations have been simplified, where any bounds <? super T> or <? extends T> have been replaced by <T>, without impacting the intent of a method. A reference is provided to each method in the first column. Any type parameter and return type declared by these methods are shown in column two.

The last column in Table 16.4 indicates the function type of the corresponding parameter in the previous column. It is instructive to note how the functional interface parameters provide the parameterized behavior of an operation. For example, the filter() method returns a stream whose elements satisfy a given predicate. This predicate is defined by the functional interface Predicate<T> that is implemented by a lambda expression or a method reference, and applied to each element in the stream.

The interfaces IntStream, LongStream, and DoubleStream also define analogous methods to those shown in Table 16.4, except for the flatMapToNumType() methods, where NumType is either Int, Long, or Double. A summary of additional methods defined by these numeric stream interfaces can be found in Table 16.2.

Table 16.4 Intermediate Stream Operations

Method name	Any type parameter + return type	Functional interface parameters	Function type of parameters
distinct (p. 915)	Stream<T>	()
dropWhile (p. 913)	Stream<T>	(Predicate<T> predicate)	T -> boolean
filter (p. 910)	Stream<T>	(Predicate<T> predicate)	T -> boolean
flatMap (p. 921)	<R> Stream<R>	(Function<T,Stream<R>> mapper)	T -> Stream<R>
flatMapToDouble (p. 921)	DoubleStream	(Function<T,DoubleStream> mapper)	T -> DoubleStream
flatMapToInt (p. 921)	IntStream	(Function<T,IntStream> mapper)	T -> IntStream
flatMapToLong (p. 921)	LongStream	(Function<T,LongStream> mapper)	T -> LongStream
limit (p. 917)	Stream<T>	(long maxSize)
map (p. 921)	<R> Stream<R>	(Function<T,R> mapper)	T -> R
mapMulti (p. 927)	<R> Stream<R>	(BiConsumer<T,Consumer<R>> mapper)	(T, Consumer<R>) -> void
mapToDouble (p. 921)	DoubleStream	(ToDoubleFunction<T> mapper)	T -> double
mapToInt (p. 921)	IntStream	(ToIntFunction<T> mapper)	T -> int
mapToLong (p. 921)	LongStream	(ToLongFunction<T> mapper)	T -> long
parallel (p. 933)	Stream<T>	()
peek (p. 920)	Stream<T>	(Consumer<T> action)	T -> void
sequential (p. 933)	Stream<T>	()
skip (p. 915)	Stream<T>	(long n)
sorted (p. 929)	Stream<T>	()
sorted (p. 929)	Stream<T>	(Comparator<T> cmp)	(T,T) -> int
takeWhile (p. 913)	Stream<T>	(Predicate<T> predicate)	T -> boolean
unordered (p. 932)	Stream<T>	()