How does Kotlin handle values that can be null, and what mechanisms does it provide for this?

Kotlin has a built-in null safety system that helps avoid the common NullPointerException error. By default, types in the language cannot contain null. To allow a variable to hold null, its type is declared with a ?.

Example:

var a: String = "Hello"  // cannot be null
var b: String? = null     // can be null

To work with nullable types, Kotlin provides several mechanisms:

• Safe call (?.) — allows calling a method or property if the object is not null, otherwise returns null.

  val length = b?.length  // if b is not null, returns length, otherwise null
  

• Elvis operator (?:) — returns the value on the left if it is not null, otherwise the value on the right.

  val length = b?.length ?: 0  // if b is null, length will be 0
  

• Not-null assertion operator (!!) — asserts that the value is not null, and if it is, throws an exception.

  val length = b!!.length  // if b is null, an exception will be thrown
  

• Functions like let, run, also, and others with safe calls for working with nullable objects.

Thus, Kotlin forces explicit handling of null, reducing the likelihood of runtime errors.