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JAVASCRIPTHTMLCSSPYTHONSQLJAVACPPCSHARPPHPTYPESCRIPTCRUBYGOSWIFTKOTLINRUSTRBASHSCALAOBJECTIVE-CDARTPERLLUAMATLABXMLJSONMARKDOWNASSEMBLYLATEXYAMLSOLIDITYBLOCKCHAIN

Topics

Kotlin Basics

Introduction to KotlinInstalling KotlinKotlin SyntaxKotlin VariablesKotlin Data TypesKotlin OperatorsKotlin CommentsKotlin Input/Output

Control Flow

Kotlin If-Else StatementsKotlin When ExpressionKotlin For LoopsKotlin While LoopsKotlin Do-While LoopsKotlin Break and ContinueKotlin RangeKotlin Exceptions

Functions

Kotlin Function BasicsKotlin Function ParametersKotlin Return TypesKotlin Default ArgumentsKotlin Named ArgumentsKotlin Infix FunctionsKotlin Inline FunctionsKotlin RecursionKotlin Lambda Expressions

Object-Oriented Programming

Kotlin ClassesKotlin ObjectsKotlin ConstructorsKotlin InheritanceKotlin InterfacesKotlin Abstract ClassesKotlin Data ClassesKotlin Sealed ClassesKotlin Enum ClassesKotlin Nested ClassesKotlin Inner ClassesKotlin Visibility Modifiers

Collections

Kotlin ListsKotlin SetsKotlin MapsKotlin ArraysKotlin Collection OperationsKotlin Sequences

Null Safety

Kotlin Nullable TypesKotlin Safe CallsKotlin Elvis OperatorKotlin Not-null AssertionsKotlin Smart Casts

Functional Programming

Kotlin Higher-Order FunctionsKotlin Function TypesKotlin ClosuresKotlin CurryingKotlin Composition

Generics

Kotlin Generic FunctionsKotlin Generic ClassesKotlin Type ConstraintsKotlin Variance

Coroutines

Kotlin Coroutine BasicsKotlin Suspending FunctionsKotlin Coroutine ScopeKotlin Coroutine ContextKotlin Coroutine BuildersKotlin Coroutine DispatchersKotlin Flow

Extension Functions

Kotlin Extension Functions BasicsKotlin Extension PropertiesKotlin Companion Object Extensions

Delegation

Kotlin Delegation PatternKotlin Property DelegationKotlin Observable Properties

Reflection

Kotlin Reflection BasicsKotlin Class ReferencesKotlin Callable References

Interoperability

Kotlin-Java InteroperabilityKotlin-JavaScript InteroperabilityKotlin Native

Testing

Kotlin Unit TestingKotlin Test FrameworksKotlin Mocking

Advanced Topics

Kotlin DSLKotlin Operator OverloadingKotlin Type AliasesKotlin Inline ClassesKotlin ContractsKotlin AnnotationsKotlin Metaprogramming

Kotlin Variables

Variables are essential components in Kotlin programming. They serve as containers for storing and manipulating data. Kotlin offers a flexible and type-safe approach to variable declaration and usage.

Variable Declaration

In Kotlin, variables are declared using two keywords: var and val. The choice between them depends on whether you want the variable to be mutable or immutable.

Mutable Variables: var

Use var to declare mutable variables. These can be reassigned after initialization.

var age: Int = 25
age = 26 // Valid: value can be changed

Immutable Variables: val

Use val for read-only variables. Once initialized, their value cannot be changed.

val pi: Double = 3.14159
// pi = 3.14 // Error: val cannot be reassigned

Type Inference

Kotlin features powerful type inference. This means you often don't need to explicitly specify the variable type.

var name = "John" // Type inferred as String
val age = 30 // Type inferred as Int

The compiler automatically determines the type based on the assigned value. This leads to cleaner, more concise code.

Late Initialization

Sometimes, you might need to declare a variable without initializing it immediately. Kotlin provides the lateinit modifier for such cases.

lateinit var username: String
// ... later in the code
username = "kotlin_user"

Use lateinit cautiously, as accessing an uninitialized variable will throw an exception.

Null Safety

Kotlin emphasizes null safety. By default, variables cannot hold null values. To allow null, use the nullable type syntax.

var nullableAge: Int? = null
var nonNullableAge: Int = 25 // Cannot be null

This feature helps prevent null pointer exceptions, a common issue in many programming languages. For more on this topic, check out Kotlin Nullable Types.

Constants

For values that are known at compile-time and never change, use the const modifier with val.

const val MAX_COUNT = 100

Constants are typically declared at the top level or in object declarations.

Best Practices

  • Use val by default, and only use var when necessary.
  • Leverage type inference to write cleaner code.
  • Be mindful of null safety and use nullable types judiciously.
  • Name variables descriptively to enhance code readability.

Understanding variables is crucial for mastering Kotlin. They form the foundation for more advanced concepts like Kotlin Data Types and Kotlin Operators.