Declaring Variables in Kotlin
Understanding how to declare variables is one of the first steps to writing useful Kotlin code. In Kotlin, you declare variables using either val or var. The keyword you choose determines whether the value stored in the variable can be changed after it is first assigned.
A variable declared with val is immutable. This means that once you assign a value to a val, you cannot change it—trying to do so will result in a compilation error. Use val when you want to make sure the value does not change, like for constants or values that should remain the same throughout your program.
A variable declared with var is mutable. This means you can assign a new value to it at any time after its initial declaration. Use var when you expect the variable's value to change as your program runs.
Main.kt
12345678910111213141516171819package com.example fun main() { // Immutable variable using val val greeting: String = "Hello, Kotlin!" println(greeting) // Mutable variable using var var counter: Int = 1 println("Counter is: $counter") // Changing the value of counter counter = 2 println("Counter is now: $counter") // Uncommenting the next line would cause a compilation error // greeting = "Hi, Kotlin!" // Error: Val cannot be reassigned }
In the code above, you see both val and var in action. The greeting variable is declared with val, so its value cannot change after it is set. This is why trying to assign a new value to greeting would cause an error. The counter variable is declared with var, so you can change its value as many times as you need. This flexibility makes var useful for values that need to be updated, such as counters, accumulators, or any variable whose value is expected to change during the program's execution.
As a rule of thumb, prefer val unless you have a clear reason for a variable to be mutable. This helps you write safer and more predictable code, as you can be confident that immutable values will not change unexpectedly.
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Understanding how to declare variables is one of the first steps to writing useful Kotlin code. In Kotlin, you declare variables using either val or var. The keyword you choose determines whether the value stored in the variable can be changed after it is first assigned.
A variable declared with val is immutable. This means that once you assign a value to a val, you cannot change it—trying to do so will result in a compilation error. Use val when you want to make sure the value does not change, like for constants or values that should remain the same throughout your program.
A variable declared with var is mutable. This means you can assign a new value to it at any time after its initial declaration. Use var when you expect the variable's value to change as your program runs.
Main.kt
12345678910111213141516171819package com.example fun main() { // Immutable variable using val val greeting: String = "Hello, Kotlin!" println(greeting) // Mutable variable using var var counter: Int = 1 println("Counter is: $counter") // Changing the value of counter counter = 2 println("Counter is now: $counter") // Uncommenting the next line would cause a compilation error // greeting = "Hi, Kotlin!" // Error: Val cannot be reassigned }
In the code above, you see both val and var in action. The greeting variable is declared with val, so its value cannot change after it is set. This is why trying to assign a new value to greeting would cause an error. The counter variable is declared with var, so you can change its value as many times as you need. This flexibility makes var useful for values that need to be updated, such as counters, accumulators, or any variable whose value is expected to change during the program's execution.
As a rule of thumb, prefer val unless you have a clear reason for a variable to be mutable. This helps you write safer and more predictable code, as you can be confident that immutable values will not change unexpectedly.
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