Functional Thinking

Chapter 7. Practical Thinking

Many of the examples I’ve featured thus far are abstract, because I’m illustrating the different thinking mode required for functional programming. But at some point you have to take these lessons back to the real world.

In this chapter, I cover some real-world occurrences of functional thinking, starting with Java 8 and moving to functional architectures and web frameworks.

Java 8

I’ve shown the lambda syntax for Java 8 in numerous examples throughout the book. Rather than merely bolt higher-order functions onto the language, the Java 8 engineers made clever choices to enable older interfaces to take advantage of functional features.

In Chapter 2, I showed an example of the “company process,” along with the Java 8 solution, repeated here in Example 7-1.

Example 7-1. Company process in Java 8

    public String cleanNames(List<String> names) {
        if (names == null) return "";
        return names
                .stream()
                .filter(name -> name.length() > 1)
                .map(name -> capitalize(name))
                .collect(Collectors.joining(","));
    }

    private String capitalize(String e) {
        return e.substring(0, 1).toUpperCase() + e.substring(1, e.length());
    }

With streams in Java 8, you can chain and compose functions together until you call a function that generates output (called a terminal operation), such as collect() or forEach(). The filter() method in Example 7-1 is the same filter method I’ve shown throughout the book. The filter() method accepts a higher-order function that returns a Boolean value, which is ...