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type name, as in LongFunction ( Figure 4-2 ). If the higher-order function uses a primitive
type, it is suffixed with To and the primitive type, as in mapToLong .
Figure 4-2. LongFunction
There are also specialized versions of Stream for these primitive types that prefix the type
name, such as LongStream . In fact, methods like mapToLong don't return a Stream ; they re-
turn these specialized streams. On the specialized streams, the map implementation is also
specialized: it takes a function called LongUnaryOperator , visible in Figure 4-3 , which
maps a long to a long . It's also possible to get back from a primitive stream to a boxed
stream through higher-order function variations such as mapToObj and the boxed method,
which returns a stream of boxed objects such as Stream<Long> .
Figure 4-3. LongUnaryOperator
It's a good idea to use the primitive specialized functions wherever possible because of the
performance benefits. You also get additional functionality available on the specialized
streams. This allows you to avoid having to implement common functionality and to use
code that better conveys the intent of numerical operations. You can see an example of how
to use this functionality in Example 4-4 .
Example 4-4. Using summaryStatistics to understand track length data
public static
void printTrackLengthStatistics ( Album album ) {
IntSummaryStatistics trackLengthStats
= album . getTracks ()
. mapToInt ( track -> track . getLength ())
. summaryStatistics ();
static void
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