Kotlin Variables

Kotlin Variables – Complete Guide

In Kotlin Variables is used to store data that can be used and changed during program execution.

Kotlin variables are declared using val and var.

1. Types of Variables in Kotlin

Kotlin has two main types of variables:

val – Read-only (Immutable)
var – Mutable (Changeable)

2. `val` – Read-Only Variable

Once assigned, its value cannot be changed.

Invalid:

Safer
Preferred in Kotlin
Similar to final in Java

3. `var` – Mutable Variable

Value can be changed.

Use only when modification is required

4. Variable Declaration with Data Type

You can explicitly specify the type.

Good for readability
Helpful in large projects

5. Type Inference (Automatic Type Detection)

Kotlin automatically detects the type.

Cleaner syntax
Less boilerplate

6. Late Initialization (`lateinit`)

Used when variable will be initialized later.

Only for var
Cannot be used with primitive types

Example:

7. Nullable Variables

By default, variables cannot be null.

To allow null:

Prevents NullPointerException

8. Constant Variables (`const val`)

Compile-time constants.

Faster
Must be top-level or inside object

9. Multiple Variable Declaration

Or:

10. Variable Scope

Local Variable

Declared inside a function.

Global Variable

Declared outside all functions.

Common Mistakes

Using var instead of val
Forgetting ? for nullable variables
Using lateinit for primitives
Declaring unused variables

Best Practices

Prefer val over var
Use meaningful variable names
Keep scope minimal
Avoid unnecessary mutability

Interview Questions – Kotlin Variable

Q1. Difference between val and var?
val is immutable, var is mutable.

Q2. Can val reference mutable objects?
Yes.

Q3. What is lateinit?
Late initialization of non-null variables.

Q4. Can Kotlin variable be null by default?
No.

Summary

val → read-only
var → changeable
Type inference supported
Null safety built-in
Cleaner than Java

Kotlin Variables