Book Image

Introduction to JVM Languages

By : van der Leun
Book Image

Introduction to JVM Languages

By: van der Leun

Overview of this book

Anyone who knows software development knows about the Java Virtual Machine. The Java Virtual Machine is responsible for interpreting Java byte code and translating it into actions. In the beginning, Java was the only programming language used for the JVM. But increasing complexity of the language and the remarkable performance of the JVM created an opening for a new generation of programming languages. If you want to build a strong foundation with the Java Virtual Machine and get started with popular modern programming languages, then this book is for you. The book will begin with a general introduction of the JVM and its features, which are common to the JVM languages, helping you get abreast with its concepts. It will then dive into explaining languages such as Java, Scala, Clojure, Kotlin, and Groovy and will show how to work with each language, their features, use cases, and pros and cons. By writing example projects in those languages and focusing on each language’s strong points, it will help you find the programming language that is most appropriate for your particular needs. By the end of the book, you will have written multiple programs that run on the Java Virtual Machine and know about the differences between the various languages.
Table of Contents (15 chapters)

Creating executable programs in Clojure


Until now, we have only entered snippets of code in Clojure's interactive REPL shell. As mentioned in the previous chapter, Clojure is not bundled with a standalone compiler program. To create executable programs in Clojure, you'll have to call an ordinary Clojure macro in your code that will instruct the built-in compiler to generate JVM .class files. This macro only generates class files when Clojure compiles code and does nothing when you run code that is already compiled.

Compiling to class files without Leiningen

Let's start by creating an executable class without the build system. You'll appreciate Leiningen more when you experience the difference. Let's create this small project with a normal text editor instead of using Eclipse IDE. Create the testproject1 root directory to hold the example files, and start by creating the required subdirectories:

  • com
  • com\example
  • classes

Before Clojure writes class files, you'll have to generate JVM classes. One...