Java Reference
In-Depth Information
Method
filter
is a
stateless intermediate operation
—it does not require any infor-
mation about other elements in the stream in order to test whether the current element
satisfies the predicate. Similarly method
map
(discussed shortly) is a stateless intermediate
operation. Method
sorted
is a
stateful intermediate operation
that requires information
about
all
of the other elements in the stream in order to sort them. Similarly method
dis-
tinct
is a stateful intermediate operation. The online documentation for each interme-
diate stream operation specifies whether it is a stateless or stateful operation.
Other Methods of the
IntPredicate
Functional Interface
Interface
IntPredicate
also contains three
default
methods:
•
and
—performs a
logical AND
with
short-circuit evaluation
(Section 5.9) between
the
IntPredicate
on which it's called and the
IntPredicate
it receives as an ar-
gument.
•
negate
—
reverses
the
boolean
value of the
IntPredicate
on which it's called.
•
or
—performs a
logical OR
with
short-circuit evaluation
between the
IntPredi-
cate
on which it's called and the
IntPredicate
it receives as an argument.
Composing Lambda Expressions
You can use these methods and
IntPredicate
objects to compose more complex condi-
tions. For example, consider the following two
IntPredicate
s:
IntPredicate even = value -> value %
2
==
0
;
IntPredicate greaterThan5 = value -> value >
5
;
To locate all the even integers greater than 5, you could replace the lambda in line 46 with
the
IntPredicate
even.and(greaterThan5)
Lines 54-58 of Fig. 17.5 create a stream pipeline that
locates
the odd integers in an
Int-
Stream
,
multiplies
each odd integer by 10,
sorts
the values in ascending order and
displays
each value followed by a space.
Intermediate Operation
map
The new feature here is the
mapping
operation that takes each value and multiplies it by
10. Mapping is an
intermediate operation
that transforms a stream's elements to new values
and produces a stream containing the resulting elements. Sometimes these are of different
types from the original stream's elements.
IntStream
method
map
(line 56) receives an object that implements the
IntUnary-
Operator
functional interface (package
java.util.function
). The lambda in line 55:
value -> value *
10
implements the interface's
applyAsInt
method, which receives an
int
and maps it to a
new
int
value. Calls to
map
are
lazy
. Method map is a
stateless
stream operation.
