Functional programming isn’t more complicated than object-oriented programming and its primarily imperative coding style. It’s just a different way of approaching the same problems. Every problem that you can solve imperatively can also be solved functionally.

Mathematics builds the foundation for functional programming, making it harder to approach than an object-oriented mindset. But just like learning a new foreign language, the similarities and shared roots become more visible over time until it just clicks.

You can implement almost any of the upcoming concepts without Java lambda expression. But compared to other languages, the result won’t be as elegant and concise. The functional tools available in Java allow your implementations of these concepts and functional idioms to be less verbose and more concise and efficient.