Most reactive programming frameworks provide functional APIs for reactive programming, which makes it even easier to work with. In this section, we will build a functional reactive API and solve a problem with it. The idea is to use the concept of a stream. A stream is a data generator or source that can provide input when requested. Functional APIs provide map, filter, and consume operations on the stream. The map and the filter operations create a new stream, and the consume operation gives a EventConsumer instance. The idea is that when EventConsumer is asked to start processing, it would spawn its own producer threads and consumer threads and treat each map, filter, or consume operations as a separately scheduled operation in a producer-consumer queue. This is just to highlight what we are really trying to achieve.

For example, I will put the code to use the functional API to solve the same perfect number problem. We will replace the pseudo-method...