Mastering Lambdas

CHAPTER4

Ending Streams: Collection and Reduction

Pipelines are ended by terminal operations, which we saw in Chapter 3 are divided into three groups: search operations, reductions, and operations with side-effects. Although we surveyed all three groups then, there is much more to say about reductions; this chapter takes up that story.

Broadly speaking, reductions are operations which return a single value that in some way summarizes the values of the stream elements. But this description does not make a distinction—very important to Java programmers—between summarizing operations that create new objects and those that change their operands. Traditional ...