Programming Kotlin

Prefer val over var

To define an immutable variable–that is, a constant or a value—use val, like so:

val pi: Double = 3.14

Unlike Java, where you’d place the type before the name of the variable, in Kotlin you place the name of the variable first, then a colon, followed by the type. Kotlin considers the sequence Java requires as “placing the cart before the horse” and places a greater emphasis on variable names than variable types.

Since the type of the variable is obvious in this context, we may omit the type specification and ask Kotlin to use type inference:

val pi = 3.14

Either way, the value of pi can’t be modified; val is like final in Java. Any attempt to change or reassign a value to variables defined using val will result in ...