CS0011 Module 3

Modern, trending programming language that was released in 2016 by JetBrains

Kotlin

Kotlin is a modern, trending programming language that was released in __ by JetBrains

2016

Kotlin is a modern, trending programming language that was released in 2016 by __

JetBrains

Compatible with Java

Kotlin

Works on different platforms (Windows, Mac, Linux, Raspberry Pi, etc.)

Kotlin

Concise and safe

Kotlin

Easy to learn, especially if you already know Java

Kotlin

Free to use

Kotlin

Big community/support

Kotlin

• Mobile applications (specially Android apps)

• Web development

• Server side applications

• Data science

• And much, much more!

Uses of Kotlin

The __ keyword is used to declare a function

fun

The __ function is needed to execute a program

main()

In Kotlin, code statements do not have to end with a __ (_)

semicolon (;)

//

Single line comments

/* … */

Multi-line comments

The __ keyword can create a variable whose reference will be immutable (which cannot be modified after its initialization)

val

The __ keyword lets you create a variable whose reference will be mutable (which can be modified after its initialization)

var

Kotlin does not require you to mention the __ __ __ __ when declaring it (thanks to type inference)

type of a variable

val time = 20
val greeting = if (time < 18) {
    "Good day."
} else {
    "Good evening."
}
println(greeting)

• if

• if – else

• if – else if

• if – else expression

val time = 20
val greeting = if (time < 18)
    "Good day." else "Good evening."

• if

• if – else

• if – else if

• if – else expression

val day = 4 

val result = when (day) {
    1 -> "Monday"
    2 -> "Tuesday"
    3 -> "Wednesday"
    4 -> "Thursday"
    5 -> "Friday"
    6 -> "Saturday"
    7 -> "Sunday"
    else -> "Invalid day."
}
println(result)

// Outputs "Thursday" (day 4)

when expression

val nums = arrayOf(1, 5, 10, 15, 20)
for (x in nums) {
    println(x)
}

// for loop using arrays

• while

• do – while

• for – loop

for (nums in 5..15) {
    println(nums)
}

// for loop using range

• while

• do – while

• for – loop

class Car {
    var brand = ""
    var model = ""
    var year = 0
}

class declaration (OOP)

// Create a c1 object of the Car class
val c1 = Car() 

// Access the properties and add some values to it
c1.brand = "Ford"
c1.model = "Mustang"
c1.year  = 1969

println(c1.brand)    // Outputs Ford
println(c1.model)    // Outputs Mustang
println(c1.year)     // Outputs 1969

class instantiation (OOP)

class Car(var brand: String, var model: String, var year: Int)

fun main() {
    val c1 = Car("Ford", "Mustang", 1969)
}

using constructor (OOP)

class Car(var brand: String, var model: String, var year: Int) {
  // Class function
  fun drive() {
    println("Wrooom!")
  }

  // Class function with parameters
  fun speed(maxSpeed: Int) {
    println("Max speed is: " + maxSpeed)
  }
}

fun main() {
  val c1 = Car("Ford", "Mustang", 1969)
  
  // Call the functions
  c1.drive()
  c1.speed(200)
}

class & functions (OOP)

class Person (val _name: String) {
    // Member Variables
    var name: String

    // Initializer Blocks
    init {
        println("This is first init block")
    }

    init {
        println("This is second init block")
    }

    init {
        println("This is third init block")
    }

    init {
        this.name = _name
        println("Name = $name")
    }
}

fun main(args: Array<String>) {
    val person = Person("Abe")
}

Using init blocks (OOP)

Default value in primary constructor (OOP)

Using the secondary constructor (OOP)

inheritance (OOP)

Kotlin vs. Java:

Features: Extension Functions

Kotlin: It is already available in Kotlin

Java: In java, we need to create class

Kotlin vs. Java:

Features: Null Safety

Kotlin: It is available in Kotlin

Java: It is not available in Java

Kotlin vs. Java:

Features: Static Members

Kotlin: Kotlin doesn’t have a static member for a class

Java: It is available in Java

Kotlin vs. Java:

Features: String Templates

Kotlin: Yes, there are two types of string literals in Kotlin

Java: It is available in Java too but it doesn’t support expression like Kotlin

Kotlin vs. Java:

Features: Wildcard Types

Kotlin: It is not available in Kotlin

Java: Available in Java

Kotlin vs. Java:

Features: Smartcasts

Kotlin: Available in Kotlin

Java: Not Available in Java

Kotlin vs. Java:

Features: No Checked Exception

Kotlin: Kotlin removed exceptions entirely

Java: It is problematic in Java

Kotlin vs. Java:

Features: Operator Overloading

Kotlin: Kotlin allows users to provide a way to invoke functions

Java: Operators are tied to particular Java Types

Kotlin vs. Java:

Features: Constructors

Kotlin: It has primary constructor and secondary constructor

Java: Constructors can be used to take parameters to initialize attributes

Kotlin vs. Java:

Features: Type System

Kotlin: It gives nullability support, type inference, and universal guards

Java: There are other kinds of reference types related to the basic concept of class

Kotlin in Android

Kotlin in Android (Java)