Why don't primitive Stream have collect(Collector)?

Question

I\'m writing a library for novice programmers so I\'m trying to keep the API as clean as possible.

One of the things my Library needs to do is perform some complex c

Answer 1

I've implemented the primitive collectors in my library StreamEx (since version 0.3.0). There are interfaces IntCollector, LongCollector and DoubleCollector which extend the Collector interface and specialized to work with primitives. There's an additional minor difference in combining procedure as methods like IntStream.collect accept a BiConsumer instead of BinaryOperator.

There is a bunch of predefined collection methods to join numbers to string, store to primitive array, to BitSet, find min, max, sum, calculate summary statistics, perform group-by and partition-by operations. Of course, you can define your own collectors. Here's several usage examples (assumed that you have int[] input array with input data).

Join numbers as string with separator:

String nums = IntStreamEx.of(input).collect(IntCollector.joining(","));

Grouping by last digit:

Map groups = IntStreamEx.of(input)
      .collect(IntCollector.groupingBy(i -> i % 10));

Sum positive and negative numbers separately:

Map sums = IntStreamEx.of(input)
      .collect(IntCollector.partitioningBy(i -> i > 0, IntCollector.summing()));

Here's a simple benchmark which compares these collectors and usual object collectors.

Note that my library does not provide (and will not provide in future) any user-visible data structures like maps on primitives, so grouping is performed into usual HashMap. However if you are using Trove/GS/HFTC/whatever, it's not so difficult to write additional primitive collectors for the data structures defined in these libraries to gain more performance.