Котлин/Kotlin с нуля за 2 часа | Crash course по Kotlin
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4 months ago
Published on Aug 11, 2024
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Table of Contents
Introduction
This tutorial is designed to help you learn Kotlin from scratch in just two hours. Whether you are familiar with Java or are completely new to programming, this guide will walk you through the key concepts and functionalities of Kotlin. By the end, you’ll have a solid understanding of the language, enabling you to start building your own applications.
Step 1: Getting Started with Kotlin
- First Program: Start by writing your first Kotlin program.
- Open your Kotlin environment or IDE (like IntelliJ IDEA).
- Create a new Kotlin file.
- Write the following code to print "Hello, World!" to the console:
fun main() { println("Hello, World!") }
- Run the program to see the output.
Step 2: Understanding Variables and Data Types
- Variables: Learn how to declare variables in Kotlin.
- Use
val
for immutable variables (similar to final in Java). - Use
var
for mutable variables. - Example:
val name: String = "John" var age: Int = 30
- Use
- Data Types: Familiarize yourself with basic data types:
- Int, Double, Boolean, String, etc.
Step 3: Null Safety
- Null Safety: Understand Kotlin's approach to nullability.
- Declare a variable as nullable by appending a question mark:
var nullableName: String? = null
- Declare a variable as nullable by appending a question mark:
- Safe Calls: Use the safe call operator
?.
to avoid null pointer exceptions.- Example:
val length = nullableName?.length
- Example:
Step 4: Conditional Statements with When
- When Expression: Use the
when
construct for conditional logic.- Example:
when (age) { in 0..12 -> println("Child") in 13..19 -> println("Teenager") else -> println("Adult") }
- Example:
Step 5: Working with Loops
- Loops: Learn about different looping structures.
- For Loop: Iterate over a range or collection.
for (i in 1..5) { println(i) }
- While Loop: Continue until a condition is false.
var count = 0 while (count < 5) { println(count) count++ }
- For Loop: Iterate over a range or collection.
Step 6: Collections in Kotlin
- Collections: Understand how to use lists, sets, and maps.
- Example of a list:
val fruits = listOf("Apple", "Banana", "Cherry")
- Example of a list:
- Manipulating Collections: Learn basic operations like filtering and mapping.
Step 7: Functions in Kotlin
- Defining Functions: Create your own functions.
- Example:
fun greet(name: String): String { return "Hello, $name!" }
- Example:
- Function Parameters: Understand default and named parameters.
Step 8: Classes and Inheritance
- Creating Classes: Define classes and properties.
- Example:
class Person(val name: String, var age: Int)
- Example:
- Inheritance: Learn about open classes and inheritance.
- Use the
open
keyword to allow a class to be inherited:open class Animal class Dog : Animal()
- Use the
Step 9: Abstract Classes and Interfaces
- Abstract Classes: Define abstract classes that cannot be instantiated.
- Example:
abstract class Shape { abstract fun area(): Double }
- Example:
- Interfaces: Implement interfaces for shared behavior.
- Example:
interface Drawable { fun draw() }
- Example:
Step 10: Data Classes and Enums
- Data Classes: Use data classes for simple data holding.
- Example:
data class User(val name: String, val age: Int)
- Example:
- Enum Classes: Define a set of constants.
- Example:
enum class Direction { NORTH, SOUTH, EAST, WEST }
- Example:
Step 11: Sealed Classes and Scope Functions
- Sealed Classes: Use sealed classes for restricted class hierarchies.
- Example:
sealed class Result data class Success(val data: String) : Result() data class Error(val message: String) : Result()
- Example:
- Scope Functions: Learn about
let
,apply
,run
, etc., for simplifying code.
Conclusion
You have now covered the essentials of Kotlin programming. From basic syntax and data types to advanced concepts like classes, inheritance, and collections, you are equipped to continue your learning journey. Next steps could include exploring more complex projects or diving into Android development using Kotlin. Happy coding!