Java 8 Streams - collect vs reduce

Question

When would you use collect() vs reduce()? Does anyone have good, concrete examples of when it\'s definitely better to go one way or the other?

Answer 1

Let the stream be a <- b <- c <- d

In reduction,

you will have ((a # b) # c) # d

where # is that interesting operation that you would like to do.

In collection,

your collector will have some kind of collecting structure K.

K consumes a. K then consumes b. K then consumes c. K then consumes d.

At the end, you ask K what the final result is.

K then gives it to you.