Collectors and Statistics

Introduction to collectors

Since streams are lazily evaluated and support parallel execution, we need a special way to combine results. For this, we use a Collector.

A Collector represents a way to combine the elements of a Stream into one result. It consists of three things:

• A supplier of an initial value.
• An accumulator which adds to the initial value.
• A combiner which combines two results into one.

There are two ways to do this: collect(supplier,accumulator,combiner) or collect(Collector) (types left off for brevity).

Luckily, Java 8 comes with several built-in Collectors. You can ...