Kotlin for Android devs

Kotlin for Android devs

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  K O TL I N ANDROID Kotlin for Android dev
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  100 % interoperable withJava Kotlin for Android devs Developed by JetBrains KOTLIN
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  KOTLIN 2010 - WorkStarted 2011 - Announced 2016 - 1.0 release 2017 - 1.1 release Official Android First Class Language
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  Agenda What is Kotlin? Kotlin for Android devs Why Kotlin ? Syntax crash course Features of Kotlin QnA Hands-on Session
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  https://www.tiobe.com/tiobe-index/ Kotlin is climbingup the ladder
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  • Null referencesare controlled by the type system. • No raw types • Arrays in Kotlin are invariant • Kotlin has proper function types, as opposed to Java’s SAM-conversions • Use-site variance without wildcards • Kotlin does not have checked exceptions Kotlin fixes a series of issues that Java suffers from
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  Checked exceptions Primitive typesthat are not classes Static members Non-private fields Wildcard-types What Java has that Kotlin does not
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  KOTLIN & ANDROID Kotlincan be updated independently from the OS.
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  OOP language with functional aspects Modernand powerful language Focuses on safe concise and readable code Its a statically-typed programming language What is Kotlin ? First class tool support
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  Statically typed programming languagefor the JVM, Android and the browser What is Kotlin ? Its a statically-typed programming language
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  Statically type
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  What we getby using Java 6/7 + Android - • Inability to add methods in platform APIs , have to use Utils • NO Lambdas , NO Streams • NPE - so many of them What we need We need modern and smart coding language Why Kotlin ?
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  • Not Functionallanguage • Combines OOP and Functional Programming features • Open source • Targets JVM , Android and even JS Why Kotlin ?
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  Kotlin has lotsof advantages for #AndroiDev. By using #Kotlin, my code is simply better for it. - Annyce Davis I love #Kotlin. It's a breath of fresh air in the #AndroidDev world - Donn Felker At work we're just 100% on the #Kotlin train and yes, that includes #AndroidDev production code! - Huyen Tue Dao I enjoy writing in #Kotlin because I don't have to use a lot of #AndroidDev 3rd party libraries - Dmytro Danylyk #Kotlin enables more concise and understandable code without sacrificing performance or safety - Dan Lew
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  Why Kotlin ?
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  Variables and properties Syntax valname: String ="John" //Immutable , its final var name: String ="John" //Mutable ex: name= "Johnny" val name ="John" // Types are auto-inferred val num: int =10 //Immediate assignment var personList:List<String> = ArrayList() //Explicit type declaration
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  Syntax Immutable “Anything which willnot change is val” Mutable “If value will be changed with time use var” Rule of thumb
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  Modifiers - Classlevel For members declared inside a class : • Private - member is visible inside the class only. • Protected - member has the same rules as private but is also available in subclasses. • Internal - any member inside the same module can see internal members • Public - any member who can see the class can see it’s public members. Default visibility is public
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  Modifiers - Toplevel For declarations declared inside at the top level: • Private - declaration only visible in the same file. • Protected - not available as the top level is independent of any class hierarchy. • Internal - declaration visible only in the same module • Public - declaration is visible everywhere Default visibility is public
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  // Simple usage valmyValue = a if (a < b) myValue = b // As expression val myValue = if ( a < b) a else b
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  // when replacesswitch operator when (x) { 1 -> print("First output") 2 -> print("Second output") else -> { print(" Nor 1 or 2 ") // This block :) }
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  // for loopiterates with iterator val list = listOf("Game of thrones","Breaking Bad","Gotham") //while and do ..usual while (x > 0) { x-- } do { val y= someData() } while( y!=100)
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  // Functions inKotlin are declared using the fun keyword fun sum (a: Int , b: Int) : Int { return a + b } //or ..single line return fun sum(a: Int , b: Int , c: Int) = a + b + c //default values with functions fun sum(a: Int , b: Int , c: Int , d: Int = 1) = a + b + c + d
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  Class - bigpicture class Person(pName: String) { var name: String = "" var age: Int = -1 init { this.name = pName } constructor(pName: String , pAge: Int) : this(pName) { this.age = pAge } fun greet(): String { return "Hello $name" }
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  Class - bigpicture class Person(pName: String) { var name: String = "" var age: Int = -1 init { this.name = pName } constructor(pName: String , pAge: Int) : this(pName) { this.age = pAge } fun greet(): String { return "Hello $name" } // Instance , we call the constructor as if it were a //regular function val person = Person() val me = Person("Adit") // Kotlin - has no new keyword
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  Code // The fullsyntax for declaring a property is private var age:Int =0 get() = field set(value) { if(value>0) field = value } internal fun sum(first: Int , second: Int): Int { return first + second } Access modifier Keyword Name Param name Param type Return type
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  Code // Full syntax internalfun sum(first: Int , second: Int): Int { return first + second } // Omit access modifier fun sum(first: Int , second: Int): Int { return first + second } // Inline return fun sum(first: Int , second: Int): Int = first + second // Omit return type fun sum(first: Int , second: Int) = first + second // As a type val sum - { first : Int, second: Int -> first + second }
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  Higher order functions •Functions which return a function or take a function as a parameter • Used via Lambdas • Java 6 support
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  NULL SAFETY No more Kotlin’stype system is aimed to eliminate this forever.
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  Null Safety var a:String = "abc" a = null // compilation error var b: String? = "abc" b = null // ok // what about this ? val l = a.length // Promise no NPE crash val l = b.length // error: b can be null
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  Null Safety // Youcould explicitly check if b is null , and handle the options separately val l = if (b!= null) b.length else -1 // Or ... val length = b?.length // Even better val listWithNulls: List<String?> = listOf("A",null) for (item in listWithNulls) { item?.let { println(it) } // prints A ignores null
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  Nullability • In Java,the NullPointerException is one of the biggest headache’s • Kotlin , ‘null’ is part of the type system • We can explicitly declare a property , with nullable value • For each function, we can declare whether it returns a nullable value • Goodbye, NullPointerException
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  Data classes public classMovie { private String name; private String posterImgUrl; private float rating; public Movie(String name, String imageUrl, float rating) { this.name = name; this.posterImgUrl = imageUrl; this.rating = rating; } // Getters and setters // equals and hashCode // toString() }
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  Data classes // Justuse the keyword 'data' and see the magic data class Movie(val name: String , val imgUrl: String , val rating: Float) val inception = Movie("Inception","http:// inception.com/poster.jpg",4.2) print(inception.name) print(inception.imgUrl) print(inception.rating) // Pretty print print(inception.toString()) // Copy object val inceptionTwo = inception.copy(imgUrl= "http:// imageUrl.com/inception2.png")
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  Fun tricks fun evaluateObject(obj:Any): String { return when(obj){ is String -> "String it is , ahoy !!" is Int -> "Give me the 8 ball" else -> "Object is in space" } } fun ImageView.loadUrl(url: String) { Glide.with(context).load(url).into(this) }
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  Extensions public static booleanisTuesday(Date date) { return date.getDay() == 2; } boolean tuesdayBool = DateUtils.isTuesday(date); fun Date.isTuesday(): Boolean { return getDay() ==2 } val dateToCheck = Date() println(date.isTuesday())
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  Lambdas myButton.setOnClickListener { navigateToDetail()} fun apply(one: Int , two: Int , func: (Int, Int) -> Int): Int{ return func(one,two) } println(apply(1, 2, { a, b -> a * b })) println(apply(1, 2, { a, b -> a * 2 - 3 * b })) Higher order Functions
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  if (obj instanceOfMyType) { ((MyType)obj).getXValue(); } else { // Oh no do more } Smart Casting if (obj is MyType) { obj.getXValue() } else { // Oh no do more }
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  … and More •Visibility Modifiers • Companion Objects • Nested, Sealed Classes • Generics • Coroutines • Operator overloading • Exceptions • Annotations • Reflection • and more
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  … and EvenMore • Infix extension methods • Interfaces • Interface Delegation • Property Delegation • Destructuring • Safe Singletons • Init blocks • Enums • Multiline Strings • Tail recursion
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  CODE ❤ Kotlin Try Kotlinonline https://goo.gl/z9Hhq6 https://fabiomsr.github.io/from-java-to-kotlin/
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  QnA
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  THANK YOU @aditlal