collecting from parallel stream in java 8

Question

I want to take an input and apply parallel stream on that, then I want output as list. Input could be any List or any collection on which we can apply streams.

My co

Answer 1

The Collection object used to receive the data being collected does not need to be concurrent. You can give it a simple ArrayList.

That is because the collection of values from a parallel stream is not actually collected into a single Collection object. Each thread will collect their own data, and then all sub-results will be merged into a single final Collection object.

This is all well-documented in the Collector javadoc, and the Collector is the parameter you're giving to the collect() method:

 R collect(Collector collector)