on the JVM Fully compatible with Java libraries Expressive Syntax Coroutines Mixed paradigm: Object oriented and Functional Excellent tooling Very readable Property delegates Immutable by default Null Safety Lambdas Data classes String interpolation Cross compiles to JavaScript Cross compiles to native binary code Top level functions and properties Great for DSLs Functions are first class citizens Open Source Extension Functions
Survey, 2018 100,000 respondents That’s a lot of love ❤ Loved by Developers https://insights.stackoverflow.com/survey/2018#most-loved-dreaded-and-wanted
the language with over 97% satisfaction in our most recent survey.” https://android-developers.googleblog.com/2018/10/kotlin-momentum-for-android-and-beyond.html
aimed at beginners in programming. I’m going to be simplifying a lot of things. Code Samples available here https://github.com/haroldadmin/Hello-Kotlin
which means once a value is assigned to them, it can not change. val greeting: String = "Hello, world!” greeting = "Goodbye, world!" // Error Variables declared with ‘var’ can be changed as many times as you want. var greeting : String = "Hello, world!" greeting = "Goodbye, world!" //
val greeting = "Hello, world!" // // Compiler can figure out that this is a String You don’t have to specify the variable type explicitly, the compiler can figure it out for itself This is called Type Inference. If the variable type is obvious from its definition, the compiler will automatically figure it out too. This leads to less work on the programmer’s part, and makes the code more readable by removing unnecessary noise.
you specify the type of the variable after it’s name, you specify the function’s return after the function name. If the function code is trivial, the parenthesis may be omitted for brevity. Using this syntax, the above function can also be written as: fun returnHello() = "Hello"
be omitted for brevity. Using this syntax, the last function can also be written as: fun returnHello(): String = "Hello" fun returnHello() = "Hello" Type inference works for functions too. We can further shorten the above function to:
a special return type called ‘Unit’. Kotlin does not have a ‘void’ keyword or type. fun greet(): Unit { println("Hello!") } If no return type is specified, then the compiler assumes it to be Unit. fun greet() { println("Hello!") }
not modify the value of input parameters. You can, however, modify any vars outside the function scope. var outerName = "Java" fun myPrint(name: String): Unit { name = "C++" // Error outerName = "Kotlin" // ( }
Kotlin however, has an elegant solution to this problem: String Interpolation fun myPrint(name: String) { println("My name is ${name}") } myPrint("Kotlin") // Output = "My name is Kotlin
} String interpolation allows you to put values into Strings using an elegant syntax, without having to concatenate things or printing things out in multiple steps.
of the variable = Array of Integers Standard Library function to build Arrays Or, simply: val fourEvenNumbers = arrayOf(0, 2, 4, 6) // Type Inference is awesome
size. Once initialised, elements can’t be added or removed. Use Lists for dynamically sized collections. val fourOddNumbers: Array<Int> = arrayOf(0, 1, 3, 5) fourOddNumbers.add(9) // Error fourOddNumbers.remove(0) // Error Elements in an array can be accessed using their Index. Kotlin has zero based indexing, just like normal programming languages. val fourOddNumbers: Array<Int> = arrayOf(0, 1, 3, 5) println(fourOddNumbers[0])
of the variable = List of Integers Standard Library function to build lists Or, if you want a list that can be mutated: val fourEvenNumbers: MutableList<Int> = mutableListOf(0, 2, 4, 6) Mutable List of Integers
into one entity. This is useful for modelling real world things class Person() { // Contents of your class } Data = Variables inside the class Methods = Functions inside the class
the class. They are declared in the constructor, just after the name of the class class Person(val name: Int, val age: Int) { // Contents of the class } A new instance of this class can be created by supplying the values of all the properties in the constructor. The ‘new’ keyword is not required in Kotlin val kshitij = Person("Kshitij", 21)
of that class. class Person(val name: Int, val age: Int) { fun greet() { println("Hello, $name") } } These functions can be accessed through objects of this class. val kshitij = Person("Kshitij", 21) kshitij.greet()
Single Inheritance. In Kotlin, classes are final by default, which means no other class can inherit from them. To make a class inheritable, you have declare it with the ‘open’ keyword. open class Animal(val numberOfLimbs: Int) class Dog(): Animal(numberOfLimbs = 4)
that does not implement some of its functionality: Whether it be functions, or properties. Abstract classes are used when it makes sense to share some trait between a lot of classes, but that common trait is slightly different for each one. abstract class Animal(val numberOfLimbs: Int) { abstract fun interact() }
but each Animal does it slightly differently. Therefore, it makes sense to use an Abstract class with an unimplemented ‘interact’ function here. All subclasses of Animal will have their own implementation. abstract class Animal(val numberOfLimbs: Int) { abstract fun interact() } class Cat(): Animal(numberOfLimbs = 4) { override fun interact() { println("Meow!") } } class Dog(): Animal(numberOfLimbs = 4) { override fun interact() { println("Woof woof!") } }
They are used to provide a common contract different implementations of an interface. While a class can only inherit from only one super class, it can implement any number of interfaces. Therefore, interfaces are a much better method of achieving Polymorphism. interface MobilePhone { fun call() fun text() }
passed as parameters to other functions • They have a set of Inputs and a Single output, just like regular functions. • Great for scenarios where you have to pass an action, instead of a value to some other object. • Lambdas are really, like really, freakin’ cool ,
have a one or more inputs. In this case, the input is just one number. • The inputs are separated from the body of the lambda with an arrow: ‘->’ • The body of the lambda is executed, and the value of the last expression becomes the return value of the lambda. In this case, the last expression is: number % 2 == 0 • This expression evaluates to a boolean, and therefore the lambda’s return value is a Boolean. { number -> number % 2 == 0 }
definition takes in a lambda as a parameter. • The lambda takes in an integer, and returns a boolean value. How that boolean value is calculated depends on the body of the lambda function. • This flexibility of deciding the value of the lambda makes the filter function very powerful. We can easily change the condition in the lambda to return a completely different result from the filter function. list.filter({ number -> number % 2 == 0 }) fun filter(predicate: (Int) -> Boolean): List<Int>
0 }) list.filter { i -> i % 2 == 0 } If a function takes in a lambda as its last input parameter, the lambda can be written outside the parenthesis of input arguments. While this may not seem like a big deal in this case, it increases code readability exponentially in more complex functions.
}) list.filter { it % 2 == 0 } If the lambda has only one input parameter, such as in the above case, you don’t need to explicitly name the parameter. You can refer to it using the keyword ‘it’
0 } Lambdas = Readability++ fun filterEvenNumbers(list: List<Int>): List<Int> { val listOfEvenNumbers = mutableListOf<Int>() for (i in list) { if (i % 2 == 0) { listOfEvenNumbers.add(i) } } return listOfEvenNumbers } vs
classes Extension Functions Infix Functions Tail Recursive calls Even More Syntactic Sugar Interoperability with Java Generics Init Blocks Input/Output And a lot more things. Follow me on Twitter and Github to stay up to date! Find my Kotlin Android apps and other projects on GitHub/Gitlab. @haroldadmin
is a beautiful, pragmatic, and elegant language. It makes writing code a pleasure. Language website https://www.kotlinlang.org Link to these slides https://speakerdeck.com/haroldadmin/hello-kotlin Link to code samples https://github.com/haroldadmin/Hello-Kotlin Kotlin bootcamp by Google https://in.udacity.com/course/kotlin-bootcamp-for-programmers--ud9011 Join the slack channel http://slack.kotlinlang.org/
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