Any intermediate step affects the entire stream pipeline. There is no recognizable rule behind your wish that the noDiscardingFilter
step affects what the subsequently chained map
will do, but not the collect
operation. If you want to have a conditional function, it would be much clearer to implement it as such:
public static <T> Function<T,T> conditional(
Predicate<? super T> p, Function<T, ? extends T> f) {
return obj -> p.test(obj)? f.apply(obj): obj;
}
This can be used as
assertEquals(Stream.of(1, 2, 3)
.map(conditional(x -> x!=1, x -> x*10))
.collect(Collectors.toList()),
Arrays.asList(1, 20, 30)
);
or
Stream.of(1, 5, null, 3, null, 4)
.map(conditional(Objects::isNull, x -> 0)) // replacing null with default value
.forEach(System.out::println);
or
Stream.of(1, 5, null, 3, null, 4)
.map(conditional(Objects::nonNull, x -> x*10)) // null-safe calculation
.forEach(System.out::println);
Note how in these use cases, it is immediately recognizable that the predicate and function passed to conditional
belong to the same scope, which is different from the chained stream operations.
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