Kotlin From Scratch: A Complete Crash Course

This blog post summarizes a YouTube video providing a complete crash course on Kotlin, a modern programming language. It covers the basics of Kotlin, its history, use cases, setup, and fundamental concepts like variables, operators, classes, objects, inheritance, and more. Let's dive in!

What is Kotlin?

Kotlin is a statically typed, objectoriented language that primarily targets the Java Virtual Machine (JVM), Android, and JavaScript. In the Android domain, Kotlin is becoming increasingly popular due to its simplicity and powerful features compared to Java. Anything Java can do, Kotlin can handle, often with more concise code.

It was developed and maintained by JetBrains and is opensource under the Apache 2 OSS license. Launched in 2016, Kotlin quickly gained popularity, especially after being declared the official language for Android development by Google in 2017.

Why Kotlin?

Kotlin combines objectoriented and functional programming features. It emphasizes practicality and is designed to be developerfriendly. Key advantages include:

Conciseness: Write 40% less code compared to Java.
Null Safety: Avoid NullPointerExceptions, a common issue in Java.
Interoperability: 100% interoperable with Java code, allowing mixed projects.
Modern Features: Operator overloading, lambda expressions, string templates, and more.
Tooling: Excellent tooling support from JetBrains.

Where is Kotlin Used?

Kotlin is widely used for:

Building Android applications
Frontend development through compilation to JavaScript
Web development and serverside applications
JVMbased applications

Many industry giants, including Pinterest, Coursera, and Atlassian, rely on Kotlin for their projects.

Setting Up Your Kotlin Development Environment

There are two main ways to set up your Kotlin environment:

Kotlin Playground: A simple online environment (play.kotlinlang.org) for writing and running Kotlin code without any installation.
Integrated Development Environment (IDE): Any IDE supporting Java, such as IntelliJ IDEA or Eclipse, can be used. IntelliJ IDEA Community Edition is a good, free option. Ensure you have Java installed (JDK).

Kotlin Fundamentals

Variables (`var` and `val`)

Kotlin uses var and val to declare variables:

var: Declares a mutable variable (its value can be changed).
val: Declares an immutable variable (its value cannot be changed after initialization like `final` in Java).


 var name = "Scaler"
 name = "Scaler Academy" // Valid

 val pi = 3.14
 // pi = 3.1415 // Invalid  val cannot be reassigned

Data Types

Kotlin supports various data types, including:

Int: Integer numbers.
Double: Floatingpoint numbers.
Boolean: True or false values.
String: Textual data.
Char: Single characters.

Operators

Kotlin supports standard operators:

Arithmetic:+, , *, /, % (modulus).
Relational:>, <, >=, <=, ==, !=.
Increment/Decrement:++, (pre and post).


 var a = 10
 var b = 5
 println(a + b) // Output: 15
 println(a > b) // Output: true
 println(a++) // Output: 10 (postincrement)

Control Flow (`if`, `else`, `when`, Loops)

Kotlin uses if/else for conditional execution. The when expression provides a more concise alternative for multiple conditions:


 val number = 2

 when (number) {
 0 > println("Zero")
 1 > println("One")
 2 > println("Two")
 else > println("Other")
 }

Kotlin offers loops for repetitive tasks:

while: Executes a block of code as long as a condition is true.
dowhile: Executes a block of code at least once, then continues as long as a condition is true.
for: Iterates through a range, collection, or other iterable object.


 var i = 1
 while (i <= 5) {
 println("Line $i")
 i++
 }

 for (x in 1..5) {
 println(x)
 }

Functions

Functions are blocks of code that perform specific tasks. They are declared using the fun keyword:


 fun sum(a: Int, b: Int): Int {
 return a + b
 }

 fun main() {
 val result = sum(5, 3)
 println("Sum of 5 and 3 is $result")
 }

Kotlin supports function overloading (multiple functions with the same name but different parameters).

Classes and Objects

Kotlin is an objectoriented language. Classes are blueprints for creating objects. Objects are instances of classes.


 class Person(val name: String, var age: Int) {
 fun canVote(): Boolean {
 return age >= 18
 }
 }

 fun main() {
 val person1 = Person("Alice", 25)
 println("${person1.name} can vote: ${person1.canVote()}")
 }

Kotlin provides primary and secondary constructors for initializing class properties. Visibility modifiers (private, public, protected, internal) control the accessibility of class members.

Inheritance

Inheritance allows you to create new classes from existing ones. The existing class is the base class (parent), and the new class is the derived class (child). The open keyword is required on classes that are intended to be inherited from.


 open class Vehicle(val make: String) {
 fun startEngine() {
 println("Engine started!")
 }
 }

 class Car(make: String, val model: String) : Vehicle(make) {
 fun drive() {
 println("Driving the $model made by $make")
 }
 }

 fun main() {
 val myCar = Car("Toyota", "Camry")
 myCar.startEngine()
 myCar.drive()
 }

Arrays

Arrays are collections of elements of the same type.


 val numbers = arrayOf(1, 2, 3, 4, 5)

 for (number in numbers) {
 println(number)
 }

Building a Simple Android Application with Kotlin

The blog post then transitions into demonstrating how to build Android applications using Kotlin. It utilizes Android Studio and touches on the setup process.

Key Android Development Concepts Covered:

Android Studio: Setting up and familiarizing yourself with the IDE.
Project Structure: Understanding the manifest, java, and res directories.
UI Design: Using XML to create layouts (activity_main.xml).
Activities: Understanding activities as screens in the app.
Intents: Navigating between activities (explicit intents).
Event Handling: Responding to user interactions (button clicks).
Resource Management: Using images, colors, and strings from the res directory.
Thirdparty Libraries: Integrating libraries like Picasso for image loading and Retrofit for API calls.
List Views and Recycler Views: Creating scrolling lists of data.

Building a Calculator Application

The blog post uses a Calculator application as an example:

Input fields: Use EditText to get numerical inputs from the user.
Buttons: Add buttons for basic operations (+, , *, /).
Logic: Write Kotlin code to perform the calculations based on user input.
Output: Display the result using a TextView.

The tutorial explains how to set up the UI, link elements to code, perform calculations, and display the result. It also touches upon how to deal with API's and external data sources. Also it goes over building UI's with style.xml and theme.xml to centralize design choices.

Conclusion

This crash course provides a solid foundation for learning Kotlin and building Android applications. By following the steps outlined in this blog post, you can start creating your own projects and explore the vast capabilities of Kotlin in the world of mobile app development.