6.7.1 Java Before Java 8

Limitations in Java Before Java 8

Before the advent of Java 8, Java lacked the native support for treating functions as first-class citizens, which severely limited the ability to perform functional programming. Unlike languages like Clojure, where functions can be passed as arguments, returned from other functions, or assigned to variables, Java developers had to resort to lesser-optimal workarounds. This section explores those limitations and the commonly employed techniques to cope with them.

The Challenge: No First-Class Functions

Java, before version 8, inherently mandated an object-oriented programming model. Here, everything revolved around the concept of classes and objects. Functions were tightly coupled within classes, making it difficult to manipulate them independently.

Workaround: Anonymous Inner Classes

To achieve something akin to functional programming, Java developers often used anonymous inner classes. An anonymous inner class is a way to implement an interface or extend a class concurrently with its creation. While effective, the approach was notoriously verbose and far from elegant.

// Java example: Runnable interface implementation using anonymous inner class
Thread thread = new Thread(new Runnable() {
    @Override
    public void run() {
        System.out.println("Running in a thread");
    }
});
thread.start();

The code snippet above illustrates how a simple function-like task requires elaborate code, evident from the necessity of implementing a full interface. For small, succinct tasks, this verbosity became a notable downside.

The Verbosity Problem

Consider the impact of writing numerous lines of boilerplate code just to define a simple piece of functionality. This verbosity not only burgeoned lines of code but also obfuscated the core logic. Additionally, maintaining and refactoring such code bases posed challenges.

Bridging Java with Clojure’s Elegance

In a language like Clojure, such functional constructs are inherently simpler:

; Clojure example: Using an anonymous function (lambda)
(defn execute-thread []
  (let [thread (Thread. #(.println System "Running in a thread"))]
    (.start thread)))

(execute-thread)

Clojure’s ergonomic syntax highlights its emphasis on functions as first-class entities. It’s evident from the minimalistic form required for executing similar tasks.

Transition to Java 8

Java 8 marked a paradigm shift with the introduction of lambda expressions, enabling more direct manipulation of code similarly seen in functional programming languages. While we’ll delve deeper into Java’s evolution in sections 6.7.2, understanding the pre-8 era offers invaluable insight into the restrictive nature of earlier Java versions.