What is Kotlin?
Kotlin is an open source language developed by JetBrains, the company behind IntelliJ IDEA which Android Studio IDE is based. This language was created with JAVA developers in mind.
What are the advantages of the language?
It’s more expressive: this is one of its most important qualities. You can write and create more with less code.
It’s safer: Kotlin is null safe because this language gives us the opportunity to avoid NullPointerExceptions easilier.
It’s reliable: basically a mature language object oriented language. It was introduced in 2011, which means it had already gone through a number of Beta and Alpha versions before the first release (1.0)
It makes use of extension functions: This means we can extend any class with new features even if we don’t have access to the source code.
It’s highly interoperable: You can continue using most libraries and code written in JAVA, because the interoperability between both languages is good.
It’s very intuitive and easy to learn for JAVA developers. The learning curve is less for Java Devs because Kotlin has an intuitive syntax similar to Java. Of course, Java programmers should study a little bit the new methods, functions and the best practices of developing in Kotlin.
Semicolons are not necessary: While you can use them, semicolons are not necessary and it’s a good practice to avoid them (the IDE will warn you).
Kotlin Disadvantages
Kotlin is a good new language to code android apps but it isn’t perfect. All developer have been giving their feedbacks since it came to light and Google presented it as a new official language.
No namespaces
Kotlin keeps all function and properties as top level of files. It is a good feature but it can create a confusion by having a function with the same name inside the class and the library that is being imported.
The issue of Runtime Size
Due to standard library and runtime of Kotlin, your apk size will go up by extra 800 KB. This may become a problem for apps with large size since users don’t download heavy apps.
Slow compilation
A small project could take more compilation time than Java. I noticed performance is fine with any Java packages, but it is 10x slower in autocompletion, code analysis, typing, and compilation for the very small Kotlin package. This is simply unacceptable.
Small Support Community
Since it is new, very few people are using it, it could have some rare problems hence you have to solve yourself.
Conclusion
Kotlin is described as "Java++" because it's a natural evolution of the language and can do the same things with less frustration.
This language has potential but please, do not abuse it. With great power comes great responsibility - Uncle Ben.
Have a nice day!