Kotlin Programming: The Big Nerd Ranch Guide, First Edition

Compile Time vs Runtime

Kotlin is a compiled language, meaning that your program is translated into machine-language instructions prior to execution by a special program, called the compiler. During this step, the compiler ensures that certain requirements are met by your code before the instructions are generated. For example, the compiler checks whether null is assigned to a nullable type. As you have seen, if you attempt to assign null to a non-nullable type, Kotlin will refuse to compile your program.

Errors caught at compile time are called compile-time errors, and they are one of the advantages of working with Kotlin. It may sound odd to say that errors are an advantage, but having the compiler check your work during development ...