Java SE 8 Lambdas and Streams - Java: How to Program Early Objects - page 767

• Class OptionalDouble 's getAsDouble method returns the double in the object or throws a
NoSuchElementException . To prevent this exception, you can call method orElse , which returns
the OptionalDouble 's value if there is one, or the value you pass to orElse , otherwise.
• IntStream method summaryStatistics performs the count , min , max , sum and average opera-
tions in one pass of an IntStream 's elements and returns the results as an IntSummaryStatistics
object (package java.util ).
Section 17.3.3 Terminal Operation reduce
• You can define your own reductions for an IntStream by calling its reduce method. The first
argument is a value that helps you begin the reduction operation and the second argument is an
object that implements the IntBinaryOperator (p. 740) functional interface.
•Method reduce 's first argument is formally called an identity value (p. 740)—a value that, when com-
bined with any stream element using the IntBinaryOperator produces that element's original value.
Section 17.3.4 Intermediate Operations: Filtering and Sorting IntStream Values
• You filter elements to produce a stream of intermediate results that match a predicate. IntStream
method filter (p. 741) receives an object that implements the IntPredicate functional inter-
face (package java.util.function ).
• IntStream method sorted (a lazy operation) orders the elements of the stream into ascending
order (by default). All prior intermediate operations in the stream pipeline must be complete so
that method sorted knows which elements to sort.
•Method filter a stateless intermediate operation—it does not require any information about
other elements in the stream in order to test whether the current element satisfies the predicate.
•Method sorted is a stateful intermediate operation that requires information about all of the oth-
er elements in the stream in order to sort them.
•Interface IntPredicate 's default method and (p. 741) performs a logical AND operation with short-
circuit evaluation between the IntPredicate on which it's called and its IntPredicate argument.
• Interface IntPredicate 's default method negate (p. 741) reverses the boolean value of the Int-
Predicate on which it's called.
• Interface IntPredicate default method or (p. 741) performs a logical OR operation with short-
circuit evaluation between the IntPredicate on which it's called and its IntPredicate argument.
• You can use the interface IntPredicate default methods to compose more complex conditions.
Section 17.3.5 Intermediate Operation: Mapping
• Mapping is an intermediate operation that transforms a stream's elements to new values and pro-
duces a stream containing the resulting (possibly different type) elements.
• IntStream method map (a stateless intermediate operation; p. 742) receives an object that imple-
ments the IntUnaryOperator functional interface (package java.util.function ).
Section 17.3.6 Creating Streams of int s with IntStream Methods range and
rangeClosed
• IntStream methods range (p. 743) and rangeClosed each produce an ordered sequence of int
values. Both methods take two int arguments representing the range of values. Method range
produces a sequence of values from its first argument up to, but not including, its second argu-
ment. Method rangeClosed produces a sequence of values including both of its arguments.
Section 17.4 Stream<Integer> Manipulations
• Class Array 's stream method is used to create a Stream from an array of objects.