Streams - Java 8 Lambdas - page 37

Multiple Stream Calls
Rather than chaining the method calls, you could force the evaluation of each function indi-
vidually following a sequence of steps. Please don't do this. Example 3-24 shows our earlier
origins of bands example written in that style. The original example is shown in
Example 3-25 in order to make the comparison easier.
Example 3-24. Stream misuse
List < Artist > musicians = album . getMusicians ()
. collect ( toList ());
List < Artist > bands = musicians . stream ()
. filter ( artist -> artist . getName (). startsWith ( "The" ))
. collect ( toList ());
Set < String > origins = bands . stream ()
. map ( artist -> artist . getNationality ())
. collect ( toSet ());
Example 3-25. Idiomatically chained stream calls
Set < String > origins = album . getMusicians ()
. filter ( artist -> artist . getName (). startsWith ( "The" ))
. map ( artist -> artist . getNationality ())
. collect ( toSet ());
There are several reasons why the version in Example 3-24 is worse than the idiomatic,
chained version:
▪ It's harder to read what's going on because the ratio of boilerplate code to actual business
logic is worse.
▪ It's less efficient because it requires eagerly creating new collection objects at each inter-
mediate step.
▪ It clutters your method with meaningless garbage variables that are needed only as inter-
mediate results.
▪ It makes operations harder to automatically parallelize.
Of course, if you're writing your first few Stream -based examples, it's perfectly normal to
write code that's a little bit like this. But if you find yourself writing blocks of operations like