Nullable Types

Kotlin’s type system differentiates between nullable and non-nullable types. By default, types are non-nullable; you cannot get a null pointer exception from dereferencing it.

This is why Kotlin’s basic data types, such as Int, can map safely to Java’s primitive types, such as int, in the bytecode. Both can never be null.

Thus, all objects and types you’ve seen so far in this course were non-nullable. Trying to assign null to them would cause a compile-time error: