Book Image

Clojure for Java Developers

Book Image

Clojure for Java Developers

Overview of this book

We have reached a point where machines are not getting much faster, software projects need to be delivered quickly, and high quality in software is more demanding as ever. We need to explore new ways of writing software that helps achieve those goals. Clojure offers a new possibility of writing high quality, multi-core software faster than ever, without having to leave your current platform. Clojure for Java developers aims at unleashing the true potential of the Clojure language to use it in your projects. The book begins with the installation and setup of the Clojure environment before moving on to explore the language in-depth. Get acquainted with its various features such as functional programming, concurrency, etc. with the help of example projects. Additionally, you will also, learn how the tooling works, and how it interacts with the Java environment. By the end of this book, you will have a firm grip on Clojure and its features, and use them effectively to write more robust programs.
Table of Contents (14 chapters)
Clojure for Java Developers
Credits
About the Author
About the Reviewer
www.PacktPub.com
Preface
Index

Promises


If you are a full stack Java developer, there is a good chance that you have met promises in JavaScript.

Promises are simple abstractions that don't impose strict requirements on you; you can use them to calculate the result on some other thread, light process, or anything you like.

In Java, there are a couple of ways to achieve this; one of them is with futures (java.util.concurrentFuture) and if you want something more similar to JavaScript's promise there is a nice implementation called jdeferred (https://github.com/jdeferred/jdeferred), which you might have used before.

In essence a promise is just a promise that you can give to your caller, the caller can use it at any given time. There are two possibilities:

  • If the promise has already been fulfilled, the call returns immediately

  • If not, the caller will block until the promise is fulfilled

Let's take a look at an example; remember to use the start-thread function in the clojure-concurrency.core package:

Tip

Promises are only calculated...