Terminal operations

The Terminal operations are the most important operations of a stream pipeline. It is easy to accomplish everything without a need for any other operations. We have used already the forEach(Consumer<T>) Terminal operation to print each element. It does not return a value; thus, it is used for its side effects. But the Stream interface has many more powerful Terminal operations that do return values. The central among them is a collect() operation, which has two forms, R collect(Collector<T, A, R> collector) and R collect(Supplier<R> supplier, BiConsumer<R, T> accumulator, BiConsumer<R, R> combiner). These allow us to compose practically any process that can be applied to a stream. The classic example is as follows:

List<String> asList = stringStream.collect(ArrayList::new, 
                                           ArrayList::add, 
                                           ArrayList::addAll);

As you can see, it is implemented in a way...