Easily integrate the popular programming language Kotlin into your Android project

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The programming language Kotlin claims to be a better Java and increasingly replaces it as the most popular language for Android. Its advantages are said to be an increase in productivity due to more compact code, better performance, high security, and easy-to-read syntax. In 2018, the popular language topped the list of growing programming languages on GitHub. During its development, JetBrains developers addressed many typical Java problems. Now learn what Kotlin is, how to easily integrate the popular programming language into existing Android projects, and what problems can occur.

What is Kotlin?
Kotlin is an object-oriented and statically-typed open-source programming language designed as a JVM (Java Virtual Machine) language and developed mainly by JetBrains programmers. The first stable version has been available since 2016, and in spring 2017 Google declared Kotlin the main language for programming Android apps. Since then, numerous developers have been actively using Kotlin instead of Java. And since it is compatible with Java, you can rewrite existing Java projects in Kotlin step by step. The written programs are translated into bytecode that the JVM can read. Since the code can be translated into JavaScript, the programming language is also suitable for the Web. Incidentally, the name Kotlin comes from an island off St. Petersburg.

In addition to the official Android development environment Android Studio, Kotlin is supported via plug-in by IntelliJ IDEA, Eclipse, Apache Maven, and Gradle, among others.

Why Kotlin?
Kotlin offers several advantages over Java. One important example is the null pointer exceptions that are common in Java and usually occur during runtime. Kotlin eliminates the problem by not allowing the value of a variable to point to nothing. Otherwise, an error message will already be displayed during compilation. Note: If you write a “?” after the type, a null reference is allowed. In practice, null pointer exceptions can be avoided this way. Other advantages:

  • Interoperability with Java is given.
  • Existing classes can be extended with new functions.
  • Very simple syntax exists for Lambda functions.
  • For classes marked with data, in addition to getter and setter, toString(), copy(), hashCode() and equals() methods are generated by the compiler. You write such classes with one line of code and do not have to implement the same functions over and over again. In Kotlin, classes consist of about 20 to 30 percent less code than in Java.

The syntax is optimized for easy readability and resembles simplified Java:

  • Type definitions that are implicitly recognizable to the compiler can be omitted.
  • Semicolons at the end of lines are optional, a line break is sufficient.
  • The keyword new is omitted.

The hello world example:

//The function main represents the entry point.

fun main(args: array <string>) {
println(“Hello world in goblin.”)
}

Jetbrains is working on functions for multiplatform projects so you can write native apps for Android and iOS. Prominent use cases for the programming language include Uber, Evernote, and Pinterest.

Integrating Kotlin into Existing Android Projects
Thanks to Java interoperability, Kotlin can be easily integrated into existing projects. Code written in Java can call Kotlin code and vice versa. Kotlin requires only a small runtime library and can be easily integrated into existing Android development. The compilation is either bytecode or JavaScript. Numerous tutorials are available on the official website to help you with the first steps.

Android Studio: Add Kotlin to an existing project
As of Android Studio 3.0, Kotlin is fully supported. Therefore, you can easily add program files to an existing project and convert Java code to Kotlin.

Click File>New and select one of the Android templates.

Then a wizard opens where you select Kotlin as the Source Language.

Now complete the wizard. Alternatively, open a base file via File>New>Kotlin File/Class. If the option is not displayed, open the project window and select the Java directory. By default, the new files are stored in scr/main/java.

Convert existing Java code to Kotlin
You open a Java file and select Code>Convert Java File to Kotlin File. Alternatively, you can create a new Kotlin file, copy the Java code into it, and agree to the conversion when prompted.

Be careful with inheritance
It may happen that an IllegalArgumentException is displayed with working Java code. The cause is that with Kotlin, any type that can be called null must be explicitly specified. In older Android libraries, these nullable values are not always apparent. In such a case, check which parameters can be null.

Conclusion
Kotlin takes work away from web developers, saves a lot of code, and runs on the mature JVM. Its popularity is growing rapidly.

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