Summary of Terminal Stream Operations – Streams

Summary of Terminal Stream Operations

The terminal operations of the Stream<T> class are summarized in Table 16.5. The type parameter declarations have been simplified, where any bound <? super T> or <? extends T> has been replaced by <T>, without impacting the intent of a method. A reference is provided to each method in the first column.

The last column in Table 16.5 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 method allMatch() returns a boolean value to indicate whether all elements of a stream satisfy a given predicate. This predicate is implemented as a functional interface Predicate<T> that is applied to each element in the stream.

The interfaces IntStream, LongStream, and DoubleStream define analogous methods to those shown for the Stream<T> interface in Table 16.5. Methods that are only defined by the numeric stream interfaces are shown in Table 16.6.

Table 16.5 Terminal Stream Operations

Method name (ref.)	Any type parameter + return type	Functional interface parameters	Function type of parameters
forEach (p. 948)	void	(Consumer<T> action)	T -> void
forEachOrdered (p. 948)	void	(Consumer<T> action)	T -> void
allMatch (p. 949)	boolean	(Predicate<T> predicate)	T -> boolean
anyMatch (p. 949)	boolean	(Predicate<T> predicate)	T -> boolean
noneMatch (p. 949)	boolean	(Predicate<T> predicate)	T -> boolean
findAny (p. 952)	Optional<T>	()
findFirst (p. 952)	Optional<T>	()
count (p. 953)	long	()
max (p. 954)	Optional<T>	(Comparator<T> cmp)	(T,T) -> int
min (p. 954)	Optional<T>	(Comparator<T> cmp)	(T,T) -> int
reduce (p. 955)	Optional<T>	(BinaryOperator<T> accumulator)	(T,T) -> T
reduce (p. 955)	T	(T identity, BinaryOperator<T> accumulator)	T -> T, (T,T) -> T
reduce (p. 955)	<U> U	(U identity, BiFunction<U,T,U> accumulator, BinaryOperator<U> combiner)	U -> U, (U,T) -> U, (U,U) -> U
collect (p. 964)	<R,A> R	(Collector<T,A,R> collector)	Parameter is not a functional interface.
collect (p. 964)	<R> R	(Supplier<R> supplier, BiConsumer<R,T> accumulator, BiConsumer<R,R> combiner)	() -> R, (R,T) -> void, (R,R) -> void
toArray (p. 971)	Object[]	()
toArray (p. 971)	<A> A[]	(IntFunction<A[]> generator)	int -> A[]
toList (p. 972)	List<T>	()

Table 16.6 Additional Terminal Operations in the Numeric Stream Interfaces

Method name (ref.)	Return type
average (p. 949)	OptionalNumType, where NumType is Int, Long, or Double
sum (p. 949)	numtype, where numtype is int, long, or double
summaryStatistics (p. 974)	NumTypeSummaryStatistics, where NumType is Int, Long, or Double