Java to Kotlin

Chapter 3. Java to Kotlin Classes

The class is the basic unit of code organization in Java. How do we convert our Java classes to Kotlin, and what differences will we see when we have?

In this book, we’ll work together on the code in Travelator, our fictional trip-planning web app. Imagine that we have a feature to implement, but we want to take the opportunity to make our code a little better before we do. You’re pairing with one of Nat or Duncan (choose your favorite, just don’t let Nat know). The pair is the we in our refactoring discussions; not just your author, but also you as part of the team working on Travelator. Welcome aboard!

Source Code

We have published the Travelator source code in a public Git repository. “Using Code Examples” details how to access it.

Because this book is about refactoring, the important details are the changes, both between single commits and over longer intervals. We have tried to show everything you need to make sense of the code here in print; it helps to imagine that the last code sample shown is in the active editor pane as we talk about the changes we are about to make. If we have failed to make it make sense, or you just feel the need for more detail, then you can check out the code and follow along in IntelliJ.

A Simple Value Type

Let’s jump into the deep end of the codebase and convert some of our existing Java to Kotlin, starting with EmailAddress. This is a value type that holds the two parts of, you guessed it, an email address: ...