A brief introduction to Kotlin

1. Why Kotlin?
Yongqiang Li

2. Main Facts
• Statically typed programming language.
• Concise syntax which drastically reduces the amount of boilerplate code.
• OO + Functional programming
• Was born at JetBrains in 2010Open source, Free and under the Apache 2.0 license
• Releases
• 1.0 was released at Feb 2016
• 1.1 was released at Mar 2017
• Kotlin was officially supported by Google for Android as a “first-class” language.
(Announced in Google I/O 2017)

3. How it works with JVM?
JVM
JVM Bytecode
(.class)
.java
javac
.kt
kotlinc

4. Kotlin in Production

5. Simplify the Development
• Type can be inferred by compiler
• data class
• Function parameter default value, named parameters
• Properties
• Null safety!!!
• Smart casting
• High-order function and lambda
• …

6. Type can be inferred by compiler
Java
Kotlin

7. Data class (1)
Java
Total: 49 lines (followed the basic coding
convention, but removed the lines among
functions.)
Implemented class “Student”, which has “id”,
“name” and “age”.
Implemented all getters and setters
Implemented equals(), hashCode() and
toString()
Error-prone when the fields are removed or
added.

8. Data class (2)
Kotlin
Total: 1 lines. Compiler will do the same thing as
the Java version.
Actually, Kotlin compiler does more.

9. Function parameter default value, named
parameters (1)
Only Kotlin
supports it

10. Function parameter default value, named
parameters (2)
In Java, you have to use function
overloading.
No named parameter workaround.

11. Properties

12. Smart casting
Kotlin
Java

13. Null Safety!!!
Only Kotlin supports it
Nonnull type is different from nullable type
Null can be assigned to a Nonnull type.
Compiler will guard it

14. High-order functions and Lambda
Only Kotlin supports it.

15. …
• More features/improvements
• Extensions
• Delegation
• Inline functions
• Ranges
• when expression
• Type aliases
• Coroutines
• …

16. Interoperability
• 100% compatibility with Java code in both directions
• No need to bundle additional runtime to the app
• In D4C GUI build testing, only need one additional jar file kotlin-osgi-bundle.jar
(3.2MB)
• Backward compatibility with previous versions (such as Java 1.6, 1.7)
• Easy convert Java code to Kotlin

17. Toolchain
• Maven
• Allow Java and Kotlin to be compiled together
• In testing, successfully built Kotlin into D4C GUI
• Eclipse Kotlin Plugin – developed and maintained by JetBrains, for free
• Intellij IDEA Kotlin – Community Edition is for free
• Ktlint – coding convention, basic rules

18. Support
• Developing by JetBrains
• Great tutorial, documentation on kotlinlang.org
• Google official support forAndroid
• Open Source
• Working with Community
• Frequent Updates

19. Conclusion
• Kotlin provides a lot of new features, which allow engineers to write concise,
safe code. Productivity will be improved a lot!
• Great interoperability with Java and Kotlin is a great compliment.
• Good toolchain.
• Great support from Jetbrains, Google and community.

20. References
• Kotlin OfficialWebsite
• Kotlin and Android