Living Clojure

Chapter 4. Java Interop and Polymorphism

As already mentioned, Clojure runs on the Java virtual machine, and it uses this to its advantage. Not only is the JVM a production-hardened platform to run on, being a JVM language gives Clojure access to many different Java libraries as well as its own. We will look at how Clojure talks to Java classes in this chapter. We will also look at another way that it benefits from using Java classes for some types of polymorphism and how Clojure handles this polymorphism more generally as well.

First, we will explore Java interop.

Handling Interop with Java

When a new language comes into being, it faces the library problem. That is, to be useful in everyday situations, a language needs to do all the things that current dominant languages do. These current dominant languages have a full array of libraries that support things like parsing JSON and logging.

Clojure solved this new language library problem by running on the JVM and having interoperability with Java classes. When you use Clojure, you can use Java classes and Java libraries. Clojure builds on the strength of the production-hardened and tested JVM and existing Java libraries. In fact, many of the popular Clojure libraries in use today utilize Java libraries as fundamental building blocks. We are going to cover the most common areas that you will encounter: how to import Java libraries/classes, how to create new instances of them, and how to interact with their methods.

Note

Don’t sweat ...