Introduction to Kotlin

Kotlin is one more jvm programming language. JetBrains have been developing it since 2010. When I got known about it on some conference I worked with java 6. The project was too big and had a lot of dependencies, so it was very hard to migrate to java 7 and we even didn’t think about java 8. The main advantage of kotlin that attracted me is possibility to use additional features that can be complied to jvm 6. One more nice feature is that kotlin and java code are compatible with each other. It allows migrating step by step, class by class. For training I decided to rewrite my small project on kotlin. My feedback is below. Kotlin

The official web site is excellent. It has clear documentation, it gives everyone possibility to try kotlin online. I worked with version 0.13.1514, it is not stable version.

In short, kotlin is a modern language, fully compatible with java. It has automatic type detection, lambdas, internal protection from NPE and more other features to decrease lines of code. If you look at correct good kotlin code, you’ll notice that only necessary information is written. No excess information. Some classes are written in a one line, instead of dozens lines in java.

So far as both Kotlin and Idea are JetBrains’s products, IDE support is quite good. The Idea even can convert java code to kotlin, but anyway you have to make some corrections to this generated code. It is easy to write code from blank, IDE helps you, I even got known some syntax rules from Idea.

The main surprise I’ve found that all classes and methods in kotlin are final by default. In java we have ‘final’ keyword to make it final, but in kotlin to make class or method not final (in java term) you need to use keyword ‘open’. I had been trying for hour to understand why my aspect didn’t work until I had found out it.

While I was writing this post, there wasn’t official release yet. So, I faced with one bug:

@Rule
public var expectedException: ExpectedException = ExpectedException.none();

This code is not runnable. I’ve found the issue about it, soon it will be fixed. Also I’ve found a workaround, so it wasn’t fatal. Of course it is too early to migrate to kotlin right now, especially in commercial project. I’d wait for official release and some checkstyle instruments at least.

To add kotlin to a project you need to perform only 3 short steps:

        buildscript {
            repositories {
                mavenCentral()
            }
            dependencies {
                classpath ("org.jetbrains.kotlin:kotlin-gradle-plugin:0.13.1514")
            }
        }
        apply plugin: 'kotlin'
        dependencies {
            compile("org.jetbrains.kotlin:kotlin-stdlib:0.13.1514")
        }
Kotlin