What is the difference between var and val in Kotlin?

Question

What is the difference between var and val in Kotlin?

I have gone through this link:

KotlinLang: Properties and Fields

As stated on this link:

The full syntax of a read-only property declaration differs from a mutable one in two ways: it starts with val instead of var and does not allow a setter.

But just before there is an example which uses a setter.

fun copyAddress(address: Address): Address {     val result = Address() // there's no 'new' keyword in Kotlin     result.name = address.name // accessors are called     result.street = address.street     // ...     return result } 

What is the exact difference between var and val?

Why do we need both?

This is not a duplicate of Variables in Kotlin, differences with Java: 'var' vs. 'val'? as I am asking about the doubt related to the particular example in the documentation and not just in general.

Answer 1

In your code result is not changing, its var properties are changing. Refer comments below:

fun copyAddress(address: Address): Address {     val result = Address() // result is read only     result.name = address.name // but not their properties.     result.street = address.street     // ...     return result } 

val is same as the final modifier in java. As you should probably know that we can not assign to a final variable again but can change its properties.

Answer 2

val and var both are used to declare a variable.

var is like general variable and it's known as a mutable variable in kotlin and can be assigned multiple times.

val is like Final variable and it's known as immutable in kotlin and can be initialized only single time.

For more information what is val and var please see below link

http://blog.danlew.net/2017/05/30/mutable-vals-in-kotlin/