Parallel Stream non-concurrent unordered collector

Question

Suppose I have this custom collector :

  public class CustomToListCollector implements Collector, List> {

     @Ove         


        

Answer 1

This is not an actual answer per-se, but if I add more code and comments, it will get too many I guess.

Here is another interesting thing, actually it made me realize I was wrong in comments.

A spliterator flags need to be merged with all the terminal operation flags and intermediate ones.

Our spliterator's flags are (as reported by StreamOpFlags) : 95; this can be debugged from AbstractSpliterator#sourceSpliterator(int terminalFlags).

That is why the line below reports true:

 System.out.println(StreamOpFlag.ORDERED.isKnown(95)); // true

At the same time our terminal collector's characteristics are 32:

System.out.println(StreamOpFlag.ORDERED.isKnown(32)); // false

The result:

int result = StreamOpFlag.combineOpFlags(32, 95); // 111
System.out.println(StreamOpFlag.ORDERED.isKnown(result)); // false

If you think about this, it makes complete sense. List has order, my custom collector does not => order is not preserved.

Bottom-line: that UNORDERED flag is preserved in the resulting Stream, but internally nothing is done with it. They could probably, but they choose not to.