A Functional Approach to Java

Chapter 14. Functional Design Patterns

Functional programming’s answer to object-oriented design patterns is usually “just use functions instead.” Technically, that’s correct; it’s turtles all the way down⁠¹ with functional programming. However, coming from an object-oriented mindset wanting to augment your code with functional principles, more practical advice is required to utilize known patterns in a functional fashion.

This chapter will examine some of the commonly used object-oriented design patterns described by the “Gang of Four,”⁠² and how they can benefit from a functional approach.

What Are Design Patterns?

You don’t have to reinvent the wheel every time you need to solve a problem. Many of them have already been solved, or at least a general approach to a fitting solution exists in the form of a design pattern. As a Java developer, you most likely used or came across one or more object-oriented design patterns already, even if you didn’t know it at the time.

In essence, object-oriented design patterns are tested, proven, formalized, and repeatable solutions to common problems.

The “Gang of Four” categorized the patterns they describe into three groups:

Behavioral patterns

How to deal with responsibilities of and communication between objects.

Creational patterns

How to abstract the object creation/instantiation process, to help create, compose, and represent objects.

Structural patterns

How to compose objects to form larger or enhanced objects.

Design patterns ...